My car is a 1988 928 S4. My engine was running poorly, missing and had a vacuum leak. I had the injectors cleaned and replaced two that were bad. I found the vacuum leak using a tube to pressurize the system. It turned out to be the intake manifold gasket. I replaced the above components as well as the knock sensors and now cannot run the engine above 2000 rpm without it suddenly stopping. As if I turned the key off. The engine just turns over and will not start again. When I try to restart it turns over normally and acts as if there is no gas or spark to the engine. I jumped the fuel pump at the relay and I have fuel to the engine. As well I pulled a spark plug wire and I have spark. I then disconnected the battery and let it sit over night. The car then started and ran fine. The idle speed is 750 rpm and every thing worked as it should. The engine ran fine and idled fine from cold to hot ( ran it for 45 min). I can rev the engine up and down as long as I keep the rpms under 2000. After the engine stopped this time I let it sit for about an hour and tried to start it. After a few tries it started briefly then quite. I turned the key off and on a few times and at one point could hear the injectors clicking for a few seconds. It started and ran at idle for about 2 min then stopped and would not restart. My first thought is that I may have damaged the idle speed actuator. At the time I had the manifold off I tried cleaning it by pouring injector cleaner into it and let it soak for a few hours. I am thinking that some cleaner seeped into the idle speed actuator. Could this be the cause the problem? Can you give me any advise as to what to do next? Thank you for any consideration anyone can give to this problem.

 

Daryl, I don't think that what you did to the idle speed actuator would a) have damaged it b) be causing the problems you describe.

I think that something is convincing your car's brains (EZK and/or LH) to turn the car off above 2k rpm. If you have the WSM there's a step-by-step section. There are also snippets from that section posted on a number of sites. (Nichols' comes to mind.) It could be a loose/bad connection somewhere on the LH harness (many of which you would have been in the vicinity of when you R&R'd the intake for the gasket), it could be a bad rpm speed sensor, etc.

If the car ran above 2K prior to your repairs, the first thing I would do is check every harness connection in the vicinity of the intake - MAS, Throttle, Knock(s) , Injectors, Intake Temp, etc.

 

If your injectors were firing with the key on but the engine not running, it may be LH ecu failure.

 

Check your connection at the Temp 2 sensor, if you have one on the '88. Could be a loose connection. Hopefully anyhow.

 

David,
Thank you for your reply and leading me in the right direction! You were right. There was a poor connection. I failed to attach a ground wire at the back of the engine. Everything working properly now. Thank you. Steve, perhaps this is a ground for the injectors and that's what caused them to momentarily turn on. Thanks again.
Daryl