My Porsche 911 996 Carrera is broken AGAIN… can you help?! 

Hey friends! Just a quick note to say I’m pretty blown away by all the helpful comments offering advice. THIS IS SO MEGA! Thank you for taking the time to give a sh*t and reply. Feeling pretty stoked that such nice people watch this channel. A sincere thank you. ☘️

Regarding the idle control valve...the same part is fitted to bmw z3s which can be purchased really cheaply....i replaced mine for about £20

Hi Lee, Make sure you check the alarm module. It can be known in our old 996's to do all sorts of funny things. Had problem with my 996. Would not start intermittently. Different shops checked different things and couldn't find anything. Then started to cut out whilst driving...Anyway changed alarm module after lots of reading myself as that has sorted the problem. This was changed at Manthey after they too couldn't figure it out. I insisted on just trying a change of module and that did the trick. The problem is its under the seat and over time it can get moisuture and things affect the electronics. I can't say for sure if that's your problem of course, however just have this in the back of your mind just in case it is

This is screaming fuel pump. Your mechanic is can scope it with an oscilloscope, it will have a perfect sawtooth wave form if it's good. You should also have fuel pressure tested after shutting off to rule out the fuel pressure regulator.

Sorry to see this Lee. These things are sent to test us…and it sounds like youve been thoroughly tested! Hope you find a resolution soon and fall back in love with Little Irish once again

The warm starting problem is usually-always the Y-cable. The Y-cable is very well known problem both in 996 and 997. But never encounered it shutting down in traffic lights. What it did with me was that occasionally when warm it did not want to start, like low voltage, empty battery. But you try a few times then it is like ok again. Since I renewed it - no problems. Perhaps your's sound more like fuel/air/idle problem. MAF? Don't buy "Porsche" (by Bosch). Buy the exactly same "Bosch". It is like 40% cheaper but exactly the same. You can also buy MAF cleaning kit. Never touch the hot wire/foil with fingers. What does your voltage give while driving? Should be about 14 V when charge cycle on. Off cycle can be less, but should be above 12 anyway. I have the 1998.1 C2 but I dont remember if you can read fuel pressure from that generation OBD? My 1997 Audi S8 did that shutting down in traffic lights and it was the shift pump in the fuel tank that was working only when it wanted - until it decided to retire completely - and my OOOO left me standing at a Porsche Center :))) when I was getting spares for my baby. Old cars! One more thing came to my mind. The AOS little tubes into the plenum overflows sometimes. Last time I had my engine out the plenum had a little lake of oil in it which then lead to changing the AOS. But I think the basic problem was that I kept the oil at max level (due to the stupid IMSB stories). Now I keep it at at least 1/2 by the gauge which still keeps the IMS well submerged. My car is at 130 000 km = 81 000 miles. If I remember correct yours has quite a bit more so it could be any electric sensor, wire, earthing. Induction air would be my first guess in this case - but I think MAF is the source.

Time to replace the fuel pump, fuel filter, and injector service. Might be good to update the DME Relay too.

Have you looked into the EVAP purge valve. I had this exact issue and only when the car was warm.

My 986 suffered from not starting again if I stopped for a short time with the engine hot. Had lots of work done including the fuel pump. In the end it was bad fuel. I would get the fuel tank completely emptied and then put in fresh high octane fuel.

I would check resistance and voltage on the throttle body, also check coils, you could have coil braking down, always start from basics and not throw $$ and parts at it, could be anything simple. This is what O would do. Check fuel filter, fuel pressure, fuel pump Check live data on injectors, could hve one dirty, or one intermittent not working properly, Trow a redline bottle in it Check coils for resistance, they tend to break down with heat and give you intermittent shut offs, had this happen to a bmw 740il that I used to own back in the 2005, changed all coils ,done deal. Check throttle body for resistance and voltage You have replaced all the rest. Just my 2 cents👍🏽

My 997 had a similar problem some years ago. When the engine was hot (I.e. it ran for several hours), it was very hard to start again. The positive cable of the battery was renewed and since the the problem was solved.

I agree with those above that said to check your fuel pump and fuel pressures. In the air, cool cars this kind of behavior has happened to me several times. I first checked the auto control valve like you did. It turned out to be a bad. dME relay. I don’t know the exact particulars, but that relay has a significant impact on ECU performance, fuel pump performance, ignition performance. There’s a company named focus nine technology that makes solid-state relays with test lights on them for many 911s. Off the top of my head I do not know if they make one for the 996 luckily I have not had this challenge with my 996 turbo yet. Having two air cooled cars, I learned a long time ago that I always carry a spare. DME relay. A friend of mine has bought two 944 turbos that were supposedly not running, only to bring them home and change the DME relay and realize they ran fine. If you want to test this, it might be worth trying to find someone that has a working relay in a car that’s good, I just swapped the relay to see if it makes a difference.

Leave it with the mechanic for two weeks and let them use it every day.

Battery and or charging system issue. Note in your video @2:16 the voltage dropping when it dies.

check 180 amp wiring on alternator for melting I wonder if hooking up fuel pressure gauge before replacing pump also ignition switch would be a good place to start I wish I lived closer to you unfortunately I moved to Florida 20 years ago system voltage is huge also make engine ground is good very important ive even seen the one way valve on the fuel pump cause similar issues. good luck

I'd say it's the idle control valve that needs cleaning! You can clearly see in the clip that the old one is not closing properly. I had the same issue on my 964, ICV seemed to be working but after cleaning it the problem went away.

Hello Lee, check all the electric cables/contacts related to ignition system. Also the battery , be sure that has enough Amps . I have seen similar behavior (interruption without a fast deductible reason... (on BMW)) the owner checked everything and later discovered that the battery was not ok, despite being replaced not to long ago

I had a similar fault with my 996 and it was the fuel charcoal canister

Just watched this update Lee, sorry to see you're also having 996 maladies. My gut feeling with this is that it's related to fuel pressure, especially as it's exasperated by heat. My first checks would be checking the fuel pressure from the pump both hot and cold. I'd like to see the pressure directly after the pump and then the pressure being held at the fuel rail. My money is on either a failing fuel pump or a failing fuel pressure regulator. I hope you manage to get to the bottom of the problem soon!

I wish ....for just test driving a few days.. you could installed fuel pressure gauge mounted by front windshield (outside side). I did it to my 1980 camaro...It helped me watching nonstop fuel pressure for few days of driving hard and normal. That was my problem. I also have 2003 Porsche 911 ..175000 miles ...no problem with inside the engine yet.. Buying best gas and changing (by myself) Mobil 1 oil like crazy every 3000 miles just to be safe,

Replace the ICV. Mine seemed fine until I vacuum tested it when it was hot. Tiny, vacuum releasing cracks appeared throughout! I used one from a BMW Z3. I tested it, and it's identical.

Could it be the fuel Evap system malfunctioning?

I actually had the exact same problems on my 98 996, watching the symptoms in the video almost gave me some sort of awful flashback! In my case, i replaced the MAF (the MAF was actually giving zero readings) and the battery around the same time. It has been running for about a year now with no hickups. If the problem was to persist, i would probably try swapping out the Y-cable, like many here have mentioned. Batteries can be a bit tricky to test without a proper load testing setup, so it might initially seem just fine, but still have dead/dying cells. I have also heard stories of people recieving brand new MAF sensors that have been DOA, so it might be worth another try. I wish you the best of luck with your electrical gremlins!

I had the same problem with 30 degrees plus. But it seems 95 E10 petrol related even with one time purchase. Full throttle it will start again. Always take 98 E5 Lee.

You will find the problem. Don't give up. I know it's frustrating but the car is worth it. Happy Motoring!

How does the fuel pump sound when it primes cold vs warm? If you fill up with new cold gas on a warm engine does the problem get a little better. Do you have a mechanics stethoscope? If you do, throw it on the fuel pressure regulator and listen, do you hear a difference warm to cold, does it sound like something surging? If yes to all this maybe think about getting a pressure tester on the fuel rail and see if you need a new pump or regulator. Otherwise you’re testing continuity on hot vs cold wire harnesses for all the usual sensor suspects

Hi Lee, I would try the fuel filler cap and ensure the vent in it hasn’t become blocked. If it’s blocked then the fuel pump in the tank will be pulling against a vacuum which could cause these symptoms. After that I would try the engine ground strap, checking for a really good connection at both ends. Then check the fuel pump, either with an oscilloscope, or by swapping it out with a known good one. I didn’t notice if you mentioned any cranking issues, but if slow cranking is an issue then the Y cable should probably be replaced.

Replacing the cabel from the battery to the engine helped in my case when my 996 (99) had similar issues a few years back.

The positive cable junction block at the starter on top of the engine, toward the front, is notorious for internal corrosion. It can cause many many issues, especially when hot. I replaced mine based on the symptoms of dying when hot and slow to start when hot… along with draining battery. Low voltage can cause a lot of strange behavior. If you’ve never replaced the positive cable, you should do so regardless of your current issues. Best case scenario it solves them all. Most likely it will help you narrow things down.

Fuel vent system I guess. Hot temp = lots of vapor. No ventilation, is no fuel to feed the fuel system. Hope this helps

Intermittent issues suck. Sorry to hear. I hope you’re able to get it resolved. These old cars need our patience when things go downhill.

I had very similar issued on a 986 once. Whilst the idle control unit was working, it was operating just out of tolerance, which was ok when cold put wasn’t performing correctly a temperature. Might be worth checking the output signals when the car is warm.

Fuel ? what do you run it on, if supermarket cheep stuff I would try Shell ultimate, makes all the difference, I now even put in my diesel daily and have noticed a change. Ps I dont work for Shell by the way ! What about coil packs, are they by there sell by date, other than that the ignition barrel / wiring, somthing moving especialy if its doing in as you pull up.

The Y cable(and associated power cables) would be my 1st check. Did you notice the volts dropping on the dash.when it was playing up? Quick check is monitor volts when tuning lights(a load) on and off. If it's dropping below 13.5 v, engine bay power cables need checking.

Sounds fuel related to me pump could be getting hot and sticking. I think it’s back to basics when it happens check there’s a spark or fuel getting to the engine

Lee, sounds like a fuel issue to me. Check the FP relay first, make sure there's no dry joints. If the relay is OK, replace the fuel filter (if not already done so). If that doesn't solve your problem then replace the pump.

Sounds like you need to start live data logging to check spark / fuelling etc. Obviously now is the time to do it when it's most problematic. My first thoughts were piston rings or scoring, but if its so intermittent it must be electrical. Relay related to fuel maybe?

I have 2004 boxster S. I’m in the U.S. I have similar issue which becomes very apparent when I travel to coastal city(high humidity) in hot weather. When coming to a stop at a stop light when I push the clutch in the engine will stop unless I hold the revs up to 1000 or greater. It is less of a problem in my home city which can be just a hot but with much lower humidity. The problem started when the car was about 15 yrs. Old. I typically used 89 octane (mid-grade) but decided to use some 92 octane just see if it had ann effect. The stalling-shut down problem stopped. Strange but obviously fuel related but I don’t know in what way. I just purchased a new one from amazon for $21, appears to identical to OEM. I’ll see when it arrives.

I’m no mechanic but I had the same problem with my ‘03 996 … it was the battery cable going over the rear wheel arch to the motor. It would intermittently cut out only when the car got hot. The heat (here in Australia) would overwhelm the cable and the power to the motor would drop out ….the cable is fairly inexpensive and often gets over looked. Good luck

Hello everyone! Since we are on the topic of 996 problems, has anyone ever run into bank 2 on the passenger side running rich and causing the exhaust tip on the driver side to blacking up all the time? I feel no lack in power or drivability but haven’t be able to get to the bottom of it. Hoping somewhere here has maybe seen the same thing. Absolutely love this channel and all the amazing people here who help figure all the little bits out! Cheers from the USA! Thank you Lee!

Oh, how I know your pain ! A whole year we were chasing symptoms VERY similar to what you describe: from cold, running well for 30 minutes or more (if cold outside), then dying. Leave it for a few minutes and it would start again. 10 minutes later, dead again. I spare you the whole history of chasing electrical and fuel possible faults, as at the end it was the lambda sensor in the catalyst section that was causing „limp mode“ and then „recover please mode“. New sensor removed issues for now more than 10,000 km with NO stop, at all (and better mpg). Caveat: this was on my 964. May help, though.

Like many others, had fuel pump issues on other cars - mine was an Audi 200 quattro Avant - which exhibited almost exactly the symptoms you’re suffering. The pump is within the tank and fuels variable quality eventually kills these pumps. My guess is the pump is at the end of its life. Not the most pleasant job to remove and replace but ultimately an easy fix. Best of luck Lee!

My Early build dies this as well but 90 % of the time just catches itself before actually dying. So it bobbles between 500 and 1000 then settles down after about 4 bobbles. I’m guessing it’s the tune. It just needs more fuel. Take it to a tuner and have them read fuel tables if possible.

Hi, I am sorry to hear the issue and I hope you find a fix soon. Whilst I don’t own a 996, I have a 997 Gen 1 which uses a similar design engine. I believe I had a similar problem before and the issue went away after I replaced the Oil pressure sensor. I am not a mechanic but I hope this will help your 996 to get back in shape. Thanks

Check the fuel regenerative valve, similar symptoms and replaced a ton before finding that solution.

Surprised it wasn't the crank position sensor - had the exact same symptoms on my '98 996, that solved it completely. EDIT: Someone else mentioned the alarm module... I actually had my immobilizer rebuilt around the same time (water damaged from a clogged drain left by a previous owner). May be worth investigating. Lives under the driver's seat on LHD cars.

I would search electrical indeed. Improper grounding a cause all kind of weird things. Fuel pump for instance needs proper ground to operate correctly. Go around with an Ohm meter and look for slight higher resistances. Between metal parts.

Hi Lee, This sounds like classic DME relay symptoms to me. Order one of those and change it over. If that doesn't cure the issue keep it as a spare in the glovebox coz sooner or later it will be the issue that gets you stuck mate. they're only around £40 or so

Stuff like this is annoying!! Get a cheap scanner and check for any pending codes as soon as the engine shuts off, not the stored codes as they’ll set the check engine light on (if that’s on?)... Also test the relays, primarily fuel pump. Leave the carpet cover off or loose and see if any get hot after driving around.

Sorry for your troubles hope you get it sorted.

VACUUM LEAK!!!! Always blame the easy stuff first... if you car does not start, dont get a new engine, check the battery lol. Apply this to ur car and youll save a lot of money and headaches. Honestly, electronics just dont fail like people think they do. They work almost always without fail.... Just a thought. Sorry if u mentioned it in the vid as I am wiriting this while watching

Do you have a lightweight flywheel? If so, this might be the cause. The ECU might not be able to work as fast when revs are going down more quickly. That's at least something ive heard about. This might be a thing to check..

In tank fuel pump. I've replaced loads, I change them along with the crank sensor as a matter of course on 986 and 996s.

Could potentially be the fuel sending unit and pump. I had a similar problem and replacing those cured it.

Not on a Porsche but a bad battery gave me similar symptoms once. Almost like the coils were dropping out, but no fault codes.

Gently apply a Toyota badge in or near the engine bay of the car

Our 914 would die in hot weather when the engine was good and warm. It was a vapor lock. The solution was to move some part of the fuel system to a cooler location. When the car died it would not start until the engine had cooled down, so the symptom is not precisely like yours. Good luck.

Feel for you Lee, hope someone helps you get to the bottom of this, little Irish will be back to full health soon enough.

Monitor the fuel pressure in the rail both during cold starts and when the vehicle experiences difficulty starting,it may point to a faulty fuel pressure regulator that is not working properly when it gets heat soaked.

Not sure if your 996 has one and, but could possibly be the DME relay if it has one.

Long shot but have you checked the earthing strap Lee or possibly fuel pump?

Timing chain stretched. Or camshaft sensor or worn timing chain guides. So for my guess timing information sent to does not meet the expected timing readings.

I had similar issues with my 986. Turned out te be a defective brakebooster. This creates a vacuum leak. I had no engine light but same issues. Apparently this is a known issue and a retrofit is available to prevent the brake booster leaking.

Is it a fuel vapour lock of some sort, or ignition system?

Hey Lee, Did you get to the bottom of this? IIRC on 964 there was a copper braided strap from gearbox/starter to chassis... if not connected 100% or in poor condition...this causes the hot start issue. Not sure if 996 has the same set up? Good Luck...been there myself...expensive and frustrating!!

Lee, I have a 1999 996 and have had the exact same issues with my car and have changed all the parts you have, still have the same problem. I think I have got to the bottom of my issue which might be the same as yours. It could be either the fuel pump or fuel sender. My car cuts out at lights when hot and has erratic idle etc, it gets increasing worse when the car has low petrol, but never happens when the fuel tank is above 3/4 full, which is obviously helping the pressure of the fuel. It’s going in to have this done on the 28th May so will let you know if this cures he problem, like you I am losing confidence in the car and I don’t like driving it anymore.

Sounds like it could be a fuel related problem, maybe fuel pump or connections. Good luck sorting it out, don't give up. All the best.

Sounds like an electrical ignition system issue or fuel pump to me Lee, could be the fuel pump relay - reminds me of the dreaded DME from my 944 days! Best of luck with it 👍🏻

I use a mechanic , to work on my 996, who has been working on Porsches since the 80’s. Dealers, including Porsche, send puzzling cars, like yours, to him to work out and fix. Been using him for 15 years plus. If you would like the details then let me know

Sorry to hear about this. My guess would be a fuel pump or clogged fuel filter.

Looks like you got all the advice already 👌🏻 If the crank position sensor looked like it did coming off it might be worth while looking at its plug and cable too.

My car would run fine UNTIL it got hot. Then it would stammer, shudder and shake then shut off. Fuel pump is fine, water pump fine. My mechanic had the car for 2 weeks. We replaced the clutch, flywheel, RMS , pressure plated, slave cylinder, engine mounts. 3 days after i got her home it happened again. Then we replaced the FUEL PUMP RELAY ( a VW/Audi part 1KO 951 253) its a $20.00 part. Problem solved.

Fuel pump / fuel pressure would be my guess but swapping the alarm module as posted elsewhere would be an easy test.

Idle control valve - only tested cold - revs raising and lowering without throttle input on video

Maybe the feulpump? I had that with my Gti when it started getting hot in the summer. Took us years to get to the problem.

Corroded alternator cable. (To be more precise, alternator to starter motor.)

Hey there! Assume it’s fixed now as saw you today on the M40 Stratford direction!! Couldn’t believe it (that was me in the white Tesla Y btw) …also a fellow 996 owner though;) Great to see you Cheers 👋

1. I see you testing equipment, but I don’t see you testing equipment that is hot. What would have a significant delta between hot and cold function? 2. Electrical is pretty binary when it fails: *except*… when something else is expanding due to heat, it could be creating an unintended junction with something electrical, creating a temporary short/junction. Good luck, Lee!

I did see this happen to me in a 991.1 C2S where the engine cut out randomly, but starting it up again it was fine. However this only lasted for one tank of fuel lol, so im putting it down to th E5 Shell Vpower I put in was not great at the petrol station. Filled it again from the same place a couple weeks later and it was fine. Never put E10 in though.

I heard of someone else having this issue and iirc it was the high pressure fuel pump that needed replacing.

I'd try testing the fuel pressure at the fuel rail when hot and cold next - an easy DIY job with a basic gauge kit from ebay. I'm suprised this wasn't checked before replacing the CPS.

Just a quick thought, if you feel it is temperature related, then try retesting the ISV etc in a hotter environment? Nick Mrs Sibs hair drier perhaps and blast it whilst Andy does the multimeter? The kitchen table will be much cooler than an engine bay, so might not show up the fault. Good luck mate.

My 997 hates a hot start takes a few goes sometimes i know thats a common fault on 997 (look it up) but i live with it cos it doesnt cut out when driving.

Replace the crank sensor again, part could be faulty… it still points to this issue… if not fuel pump/evaporator good luck 🤞

What is your throttle body like? Similar to yours my gen 2 was stalling in traffic or at junctions, erratic idle, hard to start when warm, etc, but not throwing any codes. I tried a few things and I dont know why but ended up removing my throttle body and cleaned the grime from behind the butterfly. There must have been enough there to choke it up at idle and make it either hunt or die. Cleaned it up and it was like new brand again and the problem never came back. Worth doing as a quick and free DIY job so you know it is right

Could it be a bad fuel pump? Or the wiring harness/connector to the idle control valve?

Sorry to hear that Lee. Porsche ownership can be a PITA

I know on aircooled cars when the fuel pump starts to go it behaves exactly like you are describing is happening to you. Maybe want to replace that. Those things can act intermittently for a longtime before they finally quit. Best of luck.

Watching your video with the heat in mind and the fact its cranking and cutting out and what i would say as not lot ignition off ie instantly.... Its air or fuel starvation... My gut is telling me FUEL STARVATION... Cant really be sure why but just the way it died ? And struggling to start ... Ecu does have control over fuel injectors and maybe fuel pump ? .... Air i think easier to disnose and not cut out as quickly... So either fuel pump , lift pump or injectors or what controls them electronically... Just my gut from your videos... I think i would take the ecu plunge repair as cheapest rule in or out 🤞🤞🤞 🙏🙏🙏 fingers crossed buddy i feel your pain

I had similar symptoms and replaced crank sensor, turned out to be a the fuel pump was dying

Dash lights dimmed as it started to stall then went normal - my guess is battery shorting internally when hot ( that is if all grounds are good )

Hello Lee, I was wondering if you have any faultcodes from the ECU, from you recent post I think you had no fault codes right? Temperature sensitive problems often lead back electronics. It is just a thought, but if the ECU fails, causing the car to stall, it can also not write faultcodes to the ECU. Is it possible to keep a record of the OBD output for some time? Keep a dongle plugged in while using the car?

Check codes with durametric and also drive and log the drive with durametric. Then one should be able to read out where the problem is👍

Go back to the fuel process. Air lock? I don’t think pump from what you say. Fuel filter? Someone mentioned the evap? No idea but I’m thinking cats, cat sensors etc. and always make sure battery is full full.

We would be happy to look at the fuel system for you and provide some options if it is the fuel system. Protec Fuel Systems have been a supplier to Porsche Motorsport for over 14 years.

Did you not have the oil filler replaced in the last 18m? Your video helped me with the same problem and that caused me to lose revs. Because it seems to be heat related is there an issue that exposes a leak when hot? Perhaps worth having a look.

Possibly the engine bay purge fan not functioning, causing fuel evaporation when hot?

Lee, I really feel for you. I think it might have something to do with the fuel pump. I can see you are frustrated, especially when you have spent so much time and money without a result. I hope you find the solution asap!

Same with my 996 but not as bad as your one Lee

Bad O2 sensors as they are looped out when cold which may explain why this happens when hot.