Hard starting when car is hot after sitting

Does anyone have an issue with starting their 996 when the car have been sitting for 2-3 hours after a drive? My 996 starts just fine when completely cold, only take forever for the engine to start once it has been sitting for 2-3 hours after a drive. Sometime the cracking will take about 5-6 seconds before the engine catches. Never do this when the car is completely cold.

Does it flood a little and stumple to get to full idle RPM? I had a coolant temp sensor go out on my Audi and it would think the engine was cold. The ECU would then dump lots of fuel in a watm engine causing a hard start. Or, possibly the fuel pump check valve is bleeding off requiring the pump to refill the entire system before the injectors get pressure.

When did you last change your plugs? Is there black smoke when it does start?

No smoke, no stumble car starts perfect after the long cranking idles smoothly. I pop in gear and just drives right off. If it is the fuel pump check valve is bad wouldn't cold start have the same issue also?

How old are plugs and what were they gapped to? The older the plugs, the bigger the gap and the more voltage needed to get started. Obviously, it could be any number of things, including a bad tank of gas.

I had the plugs replaced about 20k miles ago. Again, if it were the plugs wouldn't I have this issue on cold start up also?

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Not necessarily as there is more resistance when warm. More resistance means less current flow. If you haven't run through your current tank of fuel, I would do that first before looking at anything bigger. Throw in another tankful from another station and see if you notice any improvement. Alot of things change when an engine is warm. You could have a leaking injector that is flooding a cylinder just slightly. Such a leak might not cause problems when the engine is cold as you need more fuel to start, but might cause a problem on a warm engine. How long have you had this problem?

I've had this problem since day one.... LOL! It's rare that I use my car after it has been parked for couple hours, it is usually 8 hours intervals, so the car is completely cold the next time I start it so I have just lived with rare issue when I need to start it. All the ideas are good, but I am not 100% convinced that's the issue. Because if I just park the car for 10-15 minutes after a drive, it will start right up. The problem only exist after a few hours. It almost seems like it is like a vapor lock problem. Where the fuel in the fuel lines are getting vaporized while the car is parked.

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Sounds like the system is bleeding off fuel pressure........

My bad, just realized you said it starts when cold.......still could be something like the coolant temp sensor.

If it coolant temp sensor wouldn't my coolant temperature be all over the place? Or not displaying the correct temperature? I have a scantool II hooked to my 996 at all times, so I see the coolant temperature reading constantly and it is displaying the correct temperature accordingly. I was just curious if anyone else have experienced this symptom, or just me. It doesn't bother me that much like I said as I rarely use the car after it has been parked for 2 hours.

Fuel injected general aviation engines are known for this problem. Tightly cowled, hot engine, sitting in the sun on a hot day and the fuel in the injection system vaporizes. Most aircraft have a proceedure for purging. I don't know anything about your car, especially about possible modifications. Have you made any modification and/or repair which might have raised the temperature in the vicinity of the injection pump and/or fuel lines? Just a WAG ( wild guess)

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My car exhibited the same symptoms just before the starter motor failed. I replaced the starter and voila, it starts everytime now.

Starter works great, cranks at the same speed cold or hot. I still think there is something fishy going on, FWIW my Ferrari does the exact same thing. Maybe is the gas? California have more % of the methenol? Is that what's in the gas in California? Would that do it?

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On Audi, two different things.........one is for the gauge and the other for the ECU. Cant comment on the 996 for sure, just offering another possibility that is relatively cheap to fix if the issue.

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The 3.4 uses a dual element sender. One drives the IC, the other the DME. However, you can check the sanity of the DME side of the sender by using the HVAC display as that will show the reading seen by the DME (using the the proprietary DME/HVAC communication bus). The 3.6 uses a single element sender and the IC captures the temperature data from the CAN bus.

Doug, Thanks for the response, I assume it is ohm reading not digital that I am looking for on the DME end?

Robin. On your 99, if the temperature sending unit goes bad, you have one of 2 things depending on which leg is broken. 1. Your temperature reading will be inaccurate or 2. Your idle speed will vary and will take longer to drop to 800 rpm after being higher. It may stick at 1000 rpm or higher for a few seconds before dropping. Jim

Robin, While I believe any of the common failure modes for the NTC temperature sender will trip the OBD-II sensor tests for plausibility (storing a code), and would probably cause problems other than just hard starting while hot, you can simply call up the coolant temperature on the HVAC display and compare it with what the dash gauge is telling you. If the digital display agrees (more or less) with the analog gauge in the instrument cluster, the DME side of the sensor is fine.

I have no codes in OBD2 except just occasional P1128, P1130 but that's pretty common on the 996s. My coolant temerature reading is super accurate, 193 F when car is in operating temp, will go up to 208F if stuck in traffic, but will maintain 193F at highway speed.