cde3

My '89 S2 75,xxx miles has developed and intermitent starting problem. Every 10-20 starts, the car will not hold the idle speed. I shut it down, restart and everything is fine. Have replaced and adjusted the TPS, but that was not it. My Mechanic is scratching his head and he is a long time 944 owner with an excellent reputation. Any suggestions on what to look at next? Thanks in advance!

Michael Stephenson

A couple of quick ideas:

Could be a bad relay connection? Remove all reinsert all of the relays, sometimes this is enough to clean the connections. Same holds true with the connections to the DME.

Beginning signs of a faulty DME Relay?

Bad wiring or bad connection in the connector to the TPS? (I have had this problem twice and jiggling the connection fixed it both times)

Skip

Best guess based on your brief description is ICV (Idle Control Valve) - located under the intake manifold, this valve controls the bypass air needed for correct idle. Is controlled by input from the DME based on engine temperature, air density, and idle speed. The valve is subject to carbon buildup (ozone) and may need to be cleaned or replaced. Common failure item above 60k miles.

There are other causes for intermittent idle irregularities, but this is the most plausible given that you have ruled out the TPS.

Good Luck!

cde3

Thank you Michael and Skip for the insights. I just got off of the phone with my mechanic and here is what we know: the spark and fuel pressure are fine so that seems to eliminate the DME, TPS and ICV as the source of the problem. However, when it happens, the engine is running really lean. If you squirt some carb cleaner in it immeadiately cures the problem. Curious.

Melchior

You may need to open up you Air Flow Meter and clean the carbon tape on the potentiometer.

Having the fuel injector pulled and cleaned($100) can also fix it. Definitely something to do anyways if the injectors have over 80K miles. Lets them last up to their design lifetime of 300K+ miles.