Tom Rathjen

I am continuing to experience problems with very rough idle at start-up on my 1988 944 (automatic). Based on advice from an early forum posting, I replaced the idle stabilizer. That did not change the behavior.

When starting the car, the idle is very rough (almost dies) until the engine has been rev'd to 2-3000 RPM for 30 seconds to a minute. Then, it runs fine. This behavior is worse on cold starts, but it also occurs even when starting the engine that has already been driven and warmed up (but turned off for any longer than 15 minutes or so....like a stop at the grocery store).

Also, note that I have followed the instructions for adjusting the idle as posted on Clarks 944 Garage Manual site.

And: it seems to me that the idle stabilizer valve is always open, even when hot. I say this because there is a drop in RPM when I disable the ISV by jumpering the B&C connectors on the test port...at any temperature. (Which also tells me that the valve itself is functioning.) So...could it be that a temp sensor or something is bad, and telling the DME to keep the ISV open all the time?

Any suggestions?

Thank you.

BugI944

If the O2 sensor sees a rich condition, the computer will allow more air into the system - to lean it out. I would first check out the entire ignition system to make sure that everything is up to speed. Plugs, wires, rotor, cap and then the coil. Look at the tips of the spark plugs - you want to see a clean tip or perhaps a tan color. If it is running rich - the tips of the plugs will be a little darker in color. If the ignition checks out - then move on to the fuel system. If only a few plugs are a different color - then I thinking fuel injectors, and perhaps need some cleaning. Use some Techtron. Check fuel pressure and see if it holds the pressure. Check your fuel filter. Make sure the fuel is of good quality as well.

Tom Rathjen

Thanks for the reply.

Of all the things you suggest, the only things I haven't already checked or replaced are the fuel filter and coil. When I replaced the plugs, the old ones looked fine. And when I checked the new onces after they were in for a couple thousand miles, they also looked fine. I also replaced the wires, and checked the rotor and cap. And cleaned injectors. And I only use quality (brand name premium) fuel. And I have verified fuel pressure.

Were you suggesting that it could be the O2 sensor? That is also something I have not touched. Is it test-able?

I wonder if a new coil would make a difference.

BugI944

I wouldn't start replacing parts *****-nilly. The O2 sensor, when in it's operating temp, should produce voltage. I don't have the spec - but you, or someone out here may have it. Check the connections on it as well.

The Fuel Filter maybe cheap insurance - if you don't know how long it has been in service, or a waste of time if it's fairly new.

When you try to start this car back up - if you hold the gas pedal to the floor - as you are cranking, and it starts better- then this would indicate a flooded condition - too much fuel. Also, look at the smoke from the tailpipe when it starts back up. What color smoke? Or no smoke. I'm still not sure if it's fuel or ignition related.

CarbonRevo

I have the same problem with my S2. The idle feels like it's running on two cylinders and it shakes the whole car. My car used to do it when I would go out and try to start it when it was cold. It'd take 3 trys to get it to run fine.

I drove it for 4 hours the other day, pulled it in the garage and restarted it 4 times, and each time it had a rough idle, then fixed itself and idled correctly. My car also will either not start or be a pita to start if it sits longer then 10-15 minutes. It normally starts back up after 30-45 minutes of sitting and cooling

I have replaced the ICM, DME temp sensor, DME relay, fuel filter, cleaned the injectors, intake, and throttle body. I have correct fuel pressure, reference sensor works.

I've been stumped as to what it is.

BugI944

It almost sounds like vapor lock. How much alcohol is in that fuel?

cbseven

yeah man, if you haven't tested the 02 sensor do it.. or if it hasn't been changed in a decade.. just go ahead and do it. this could definitely be the root to your problem.