986 will not hold idle when cold, standard items already checked

[cadetjoe]

Hello all,

My '02 base Boxster, (e-gas, 73K mi) has developed an idling problem that occurs only during cold starts. When I first crank, the engine catches and begins to rev, but will not hold idle, stalling and dying almost immediately. I can get the car started if I immediately gas it from about 3k-6k RPM for 30 seconds or so. Once it's warmed up a bit, it will hold idle as if nothing ever happened. If I restart the engine within a few hours of shutdown, again, it starts normally as if there were nothing wrong. Only when it's dead cold will it not hold idle. Never got a CEL. Here are the steps I've taken thus far:

- Pulled codes using OBD II. Only codes were a few pending ones for random cylinder misfire and misfires on 3 cylinders (i don't remember precisely which cylinders). I'm assuming these are for misfires that occur when the engine runs rough/stalls during a cold start.

- Checked air filter. Filter didn't look too dirty, was replaced <15K miles ago. I might go ahead and pop a new one in soon just to be sure its good.

- Inspected/cleaned out throttle body. It wasn't too dirty to begin with, because I cleaned it about a year and a half ago when I replaced my AOS

- Disconnected battery and reconnected to reset DME/computer.

- Changed engine coolant temperature sensor (ECT). Tested both the old an new sensors and both showed appropriate resistance for the ambient temperature. Also tested the wires leading to the ECT and those showed appropriate voltage

- Inspected all ignition coils (they all looked good) and changed spark plugs (old plugs looked normal, no oily residue or wetness)

- Did a preliminary check for vacuum leaks. After the car was warmed up, I pulled of the oil cap, and the engine started running roughly, which is to be expected. Smoothed out with cap back on. Also tried opening the AOS hose connector a bit with the same results, so it looks like the intake is holding a good vacuum. I haven't yet hooked the intake up to a vacuum gauge or smoke machine.

I don't think its the MAF, because from what I've read on the boards, a bad MAF doesn't generally cause idle problems, and my engine runs normally otherwise.

Could it possibly be a bad AOS? I replaced my original AOS only about 1 1/2 years/10K miles ago

A little more info: I recently did an oil change and a coolant drain/refill. May have slightly overfilled the oil. When I inspected the throttle body, I saw a little oil in the intake manifold, but not much. I'm not sure if this is normal or not. There wasn't really any oil in the throttle body or the intake tube that leads back to the MAF. I also noticed last time I ran the engine that there were a few drops of oil that had splashed out of the tailpipe onto the ground. In any case, I drained some oil, and oil level is now halfway between MAX and MIN.

Anyone have any thoughts on what could be causing this? I'd appreciate your advice and suggestions. Thanks!

[logray]

Is it losing fuel pressure? Have you tested fuel pump for both volume and pressure?

You can get a cheap a/c manifold test kit from harbor freight. It has the right gauge range and fitting for the fuel rails.

[wvicary]

Not a good idea to be revving a cold engine up to 6,000 RPM. Are you still getting a misfire code? I would sort out this issue first if you are then have the intake smoke tested for leaks.

The ignition coils can look fine but leak secondary voltage when cold or under load when KV demands are high.

[cadetjoe]

logray, I haven't yet tested for fuel pressure/volume. Just took a look at the Bentley manual, though, and it says that normal fuel pressure/volume testing (e.g. with an inexpensive test kit) only applies for '97-'01 models. The '02 and newer models have a non-serviceable "lifetime" fuel pump built into the fuel tank. According to Bentley, on these MY's, fuel delivery tests require PTS2 and are "beyond the scope of this manual."

wvicary, is there a simple way to test the condition of the coils? I suppose I could swap coils around and see if the misfire cylinders follow the swap.

But, somehow I don't think it's the coils since i had misfire codes on three different cylinders - I would think it rare for three coils to go bad all at the same time. I suspect the codes are a symptom of whatever else is causing the engine to stall when cold.

[logray]

The note in the Bentley manual applies to the fuel filter, not the fuel pump itself. And aside from that I would tend to disagree that anything is "lifetime". What is their lifetime designation, 100,000 miles? And what deviation from that have they tested? Nothing is "lifetime"...

A fuel pump, lines, and system on any car can be tested for pressure and volume, and the original specs from 97-01 can be used. It most certainly does not need a PST2 or PIWIS to activate the fuel pump. You can jumper the fuel pump, or activate it with Durametric.

If you are losing fuel pressure it could account for trouble starting, the need to press on the accelerator on cold start, and misfires. Perhaps once the pressure builds as the car warms, that issue goes away.

For coil testing, check out this misfire troubleshooting guide, one of the pages shows how to ohm out the coils and other steps:

http://www.renntech....attach_id=24613

Anyhow these are just ideas since it looks like you've already gone through a heap of troubleshooting.

Edited January 9, 2012 by logray

[cadetjoe]

Just wanted to leave follow-up for the issue above (I find it frustrating when someone posts an issue and doesn't follow up with what they did to fix it). My local German import shop recommended using mid-grade fuel - apparently the winter blend of premium gas used around here had been causing starting issues for the imports. I filled the tank with 89 octane - CEL came on within 5 minutes and engine started running very rough. It would blink for 20 seconds after every engine start and then go steady. However, the lower-grade fuel did seem to help cold starting - maybe because lower-grade fuel ignites easier? I carefully checked all the coils and tested their resistance and the voltage on the coil connectors and all checked out good. Then, for the heck of it, I vacuumed out the air intake (there was a little bit of leaf debris in there) and put in a new air filter. This instantly cured the engine problems I've been having, even while still running mid-grade fuel, and the CEL turned off within a couple drive cycles. I was surprised because I replaced the filter relatively recently and it didn't look too bad, but I guess looks can be deceiving. I feel a bit silly after all the troubleshooting that it was something so simple, but the symptoms were bad enough that I though it was something a lot more serious.

Anyways, thank you folks for your help and inputs. Much appreciated.

[logray]

Interesting!