I need advice, (searched for 2 hrs on the site, couldn't find anything quite like this)

My '89 L98 is idling funky. At times it idles normal, like 750 in park, 600 in drive. Sometimes, when at a stop, it will kreep from the 600 in drive to near 1000 RPM. If put into park or neutral from this kreeping, the RPMs will shoot to 1600 and hang. If I blip the throttle, it will come back down to 1100. One wierd thing is that it will sometimes, while in gear, start kreeping, then come back to normal idle.

The 1100 worries me, since that is about where limp home idles at, but the SES light stays off, and there are no codes. The SES light does work at key on, with engine off, so the bulb is good.

Another thing that has me worried is that the problem hasn't shown up on a scan tool, WHILE it is connected and scanning, but, if it happens while connected and scanning, the connection is lost.

I'm suspecting ECU fault, or intermittent CTEMP sensor fault, but I've put it on the other Ctemp sensor that I installed (car is a project car for my company and was piggybacking the stock ECU, so installed new sensor where the plug is beside the stock sensor), with no luck.

Has anyone else had this problem? Any ideas on what to try? BTW, It has a new O2 sensor. I'll hook the scan tool up tonight again to give it another chance to screw up and keep scanning. The IAC counts are high during NORMAL idle if I remember correctly, but that shouldn't cause it to act like this.

Thanks,
Jeremy

 

Well, I've driven it with the scan tool hooked up for an hour or so in city like driving, and NO problems. Normally, the problem would have occured at nearly every stop sign. I'm going to try to get the problem to occur, and THEN hook up the scan tool to see what happens. It'll probably either make the problem go away, or won't be able to connect, but I'll give it a try.

Would that indicate a zapped ECU?

 

Sounds like your on the right track with either an open loop or IAC problem. It will hard to tell whats going on without replicating the problem with the scanner hooked up. You might want to pull the IAC and clean it and see if that helps at all.

 

Well, I drove it and let the problem occur and then hooked up the scan tool, and just after you hit scan, the problem goes away completely. So, anyone got an ECU for a '89 L98?

I still plan on pulling the TB off and cleaning everything, etc... Just need to find the time and ambition. We've got a hotrod here I've been fighting a fuel harmonic problem with a deadheaded multipoint hard nylon, small ID, fuel rail/distribution system.

Arghh,
Jeremy