99 996 Hard to start warm after 1 hour.

Hi Everyone. My 99 996 has a peculiar habit of hard starting while running errands. Car ALWAYS starts fine when cold. Car also starts fine within minutes of being turned off. However, if is run then shut off for more than 1/2 hour or so, it is very hard to restart. Cranks great, just won't start. Using takes 10 sec of cranking while flooring the pedal. Once it starts, it idles smoothly and runs great. ANyone have this behavior? ANy leads on what it might be?

Same thing happens to my 04 996 whenever I fill up with gas. That' the only time it happens so I never really think about it until next time I get gas. Something to do with the gas tank venting or gas cap?

The issue doesn't seem to correlate with getting gas. Just when it has been driven and still warm (but only after sitting for 1/2 hour +), prior to that it starts right up.

I'm facing the same issue, from my research here and the guys the issue can be one of two things: 1 - Corroded starter cable, the one that runs from the alternator to the starter and the jumper block in the engine bay 2 - Bad starter Seeming your car is older i'd say it might be the cable. The way Asahi recommended I check is to do a voltage drop test. So test what the output is at the alternator and what the voltage is from the jumper block. However with this procedure - Car needs to be warm - A/C needs to be on as well as the radio and the headlights (this is so you use some voltage and can simulate the car starting) then test if the cable has gone bad and is losing voltage preventing the car from easily turning over when warm. I'm yet to do this test as I haven't had the chance

you may need some special testing equipment after KNOWING it is NOT a battery/starter issue. you would want to check for spark and fuel while it is cranking with no start. on some cars if you floor the gas pedal while cranking they go into "clear flood mode" cutting off fuel which could mean a fuel injector is leaking after shut down . bottom line is to find out if it is fuel or spark .there is just too many things that it could be ....fuel pump,relay,ecm,crank /cam sensor,fuel check valve,cranking voltage etc

Interesting. Pretty certain it is not the starter. The starter cranks free and fast while cranking. It just doesn't start. I do find that if I floor the gas pedal while cranking (only in this warm / won't start situation) it does eventually start. Anybody else experience these symptoms?

This is a not uncommon thing. My 99 did this. We replaced the Y cable and that seemed to help, although that was not a cheap fix. It can be really maddening to track down.

Ahh right sorry disregard my diagnosis steps if the voltage doesn't drop and the starter works well!

I had the same issue when my car was running. I suspect that in my case, it's related to a bad crankshaft position sensor. Heres my sensor: I figure cold starts were fine but once it got hot, the broken plastic expands and screws with it.

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Did you have any other problems from that or was it just hot starts?

there's a slight hesitation when 1st taking off on initial start up but I can't say thats CPS related as I suspect a bad variocam solenoid or spark plugs caked in oil (from scored cylinders). I'm hoping it was just spark plugs caked in oil causing a miss.

are you starting [pun] to see a pattern here.........gas cap/radio?/replaced cable and SEEMED to get better/expanding plastic/i suspect/hoping/vario/plugs. these are commonly called shot gun repairing....scatter parts at it in hopes something with fix it. given enough time you will read.....bad gas/ims/wrong oil/parked on an angle .take the car to a shop that has the latest test equipment.....they will plug in to the obd port and look at the data while cranks no start......radio on....yeah dats a good one. tinkerbell auto repair

Your IMS bearing has failed. Replace that.

You should check your spark-plugs. I had this happen to wife's BMW, hard to start and foudn out the spark plugs were bad. I was also thinking about CPS, so worth checking it out. I had that problem with the bimmer as well. Good luck... Cheers,

Without seeing the vehicle and running some diag it is hard to tell but based on the information you are giving us I see 2 possibilities. As mentioned by AWDguy it could be the crank position sensor. However when this fails it will typically cause the car to stall and not restart until it cools down. Since you said you can turn the car off and start it right back up I do not think this is the likely source of your problem. You mentioned if you hold the accelerator pedal to the floor it will start easier, based on that info I would suggest it is a problem with your EVAP purge valve. Essentially this valve is failing and flooding the cylinders with raw fuel preventing it from starting again unless you lean it would with lots of air (full throttle on the accelerator pedal). This part number is 99611012953. It is about $210 for the part. You can prove this by shutting the car off and pinching off the rubber lines after the valve. Wait the half hour and then try to restart. If it restarts without any issues then you can remove whatever you have used to pinch off the line and try to duplicate the problem again. If it is present then you know you found the culprit. Let us know how you make out.

^^ that was the other item I am replacing also.

Agree with Aspen.

I had exactly same issue , it was caused by TWO things : 1. High fuel pressure (clogged return fuel line) 2. Bad check valve in the fuel pump - read, bad fuel pump. Fuel pressure was dropping instantly to zero with the engine off. You need to test your fuel pressure.

Very helpful ideas, folks. Thank you! Definitely no hesitation or stalling when driving. I had the evap canister shutoff valve replaced in October. Is that the same as the evap purge valve?

No it is not the same thing. The purge valve is located in the engine compartment, the shutoff valve is located behind the right front wheel well near the canister.

I also had what sounds like the exact same problem shortly after I acquired my 2001 C4. Think it is why the PO sold it to the dealer. He had it into the dealer several times for "wiring issues", he replaced the battery, he replaced the starter motor, then he traded it in. Everything seemed fine until a few hot days. Read a lot on RL and figured best bet to be purge valve Aspen mentioned. Do a search on here and you will find a way to test it and try to clean it with a nine volt battery and compressed air. Did it, took about 1 hour mainly because I kept second guessing myself. Since I did it. Not one more occurrence in the last 11 months (knocking wood). The 9v battery will also tell you if it is just plan shot. I haven't researched it but it acts like a type of vapor lock scenario. Cranks like crazy but doesn't start without holding your foot to the floor for several seconds while cranking. Could be other things as others has mentioned but that would be my first bet.

I had the same problem, and when I replaced the battery, the problem went away. Didn't make a lot of sense to me, but hey, I no longer have the problem.

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So have you fix your problem? Since I have the same issue with hard start when warm. Driven, engine off, sit for around 45 mins, and to turn on again the engine started with rev to 1,000 rpm but immediately dropped to zero and stall. Then the second start needs 5 sec hard cranking with full throttle then it fired up and idling normally. But some time even the first or the second start up successful, the car will still stall after a light throttle say move off from the carpark and come to a stop at the gate (5 sec light throttle movement and stop) then it will stall again. Though after the third or fourth restart, the car run smooth for good. but sometime until I arrived the destination and push to reverse for parking, once shifted the rev can not keep stable and stall immediately. This really make me looks like a dump on the street. See how you fixed your problem so I may make some reference before go for the mechanics again. This had been dragging on for years and no fix solution. I have replaced the crank shaft sensor and fuel pump valve/sensor already, my only suspect is now is the EVAP Purge Valve as mentioned above.

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I've been having the same issues, had the fuel pump and float, crankshaft sensor, coolant sensor, and airflow sensor replaced and yet the problem persists. Car is running better than before, just cant get it to start when hot. Is this a DIY fix or need to take to my mechanic?

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Hi, turn out it was my faulty EVAP Purge Valve problem, tested it by unplugging it to start the hot engine and it runs, plug the valve back on and it immediately stalled. Replaced it last year and everything solved. Good luck to yours. An EASY DIY job.

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thanks! Do you have instructions on how to replace?

If anyone has pix replacing the valve, pls post. if no pix, where is it located/needs to be removed to locate the valve. TIA.

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Are you referring to part #99611012953? Look directly above your alternator pulley and it is the component at the top of your engine bay. I'm looking at this and the canister valve due to a code, but will try replacing my gas cap first. Also, Bosch has this part for a fraction of the Porsche price (as usual).

Many thanks, DSC. That’s the part number. Read all threads, watched YouTube videos about this long cranking while hot issue. Also ran codes, power tested battery, checked starter cable and have new gas cap for another reason. Also thought was bad gas, and ran BK44 with non ethanol fuel. All checked out fine. I don’t mind the extended cranking IF eventually starts. I now to test this valve, now knowing is easy to get to. Thanks again.

I believe trouble cranking when hot is sign starter is on the way out. I had this issue last summer, replaced the starter, never happened again. Good Luck.