[dchasepowell]

at idle my 1987 944 n/a hesitates slightly every couple seconds. im guessing that i could have vaccum leaks which are causing this, well the engine rubber is 20 years old after all. are there common areas where these leaks occur and how exactly should i go about detecting them? should i also have a look at my "idle stabalizer unit"? I dont believe that the motor mounts or balance shafts are to blame...which company has the most affordable rubber engine components like as the intake boot and such?

[OldTee]

Try to find the leak first. Use a propane torch without flame. If engine speeds up, you found the leak.
ARF

[jerome951]

There is a way to electrically disable the idle stabilizer to determine if it is bad. Look on Clark's Garage (www.clarks-garage.com), then "Garage Shop Manual", then "Idle Adjustment Speed".

If the idle stabilizer checks out fine (i.e. the problem persists after you have deactivated it), you likely have a vacuum leak. Staying clear of the fans, you can move and squeeze different hoses to see which causes a change in the engine. You can buy the properly-sized silicone vacuum hose from Lindsey Racing and others.

You could also have a bad O2 sensor, but that usually results in a periodic idle speed increase.

[Dr K]

Another possible easy fix (I had this problem on my Carrera) - the O2 Sensor wire could be loose. On the 911 there was a plug mid-wire, which had worked it's way out a little, and was intermittently losing connection. This would have been a small problem had we not been in British Columbia, but the problem was found and fixed, eventually.

Peter

PS: Welcome to the board, Chase. Photos?

[Richard Curtis]

Good preventative maintenance on cars this old: Simply replace all the vacuum hoses. Cheap and easy. Remove the Idle Air Control valve (or whatever it's called), clean it thoroughly and reinstall. Do the same with the throttle body or Vane Air Meter. If the car is equipped with a Throttle Position Sensor, these are known to go bad and cause idle problems. Some TPSes are adjustable for voltage; others aren't. Sometimes simply resetting the base idle and the TPS voltage can cure an idle problem but even then, it's usually a symptom of a worn TPS.

[Jase007]

dchase:

at idle my 1987 944 n/a hesitates slightly every couple seconds.

Richard and Jerome have good solid advice. Does it sound like the idle is failing and gets cought by the ICV [idle control valve] or ICSU?

These early bosch Motronic systems [what's in your 944] are easy to troubleshoot. If it isn't an ICV, AFM [air flow meter], intake air temp sensor in the AFM, engine temp, coolant temp or crank / flywheel position sensor it is usually a vacuum leak.

A book that I bought and have become very appreciative of and go to often is:

Charles Probst's Bosch Fuel Injection and Engine Management.




Has excellent information on K-jetronic [K-basic and K-lambda] and early motronic. These fuel injection and engine management systems are in 73.5 911s up to / through 964, 944s [all], BMW E30s, E36s, audis, VWs, and on and on. CIS = K-Jetronic]

I rec'd it whenever I can b/c applies to several makes you are likely to own of pre-1995 [or ODB I] european cars.

Cheers.