Hi I'm Dan and I need some help. I hope I posted this on the correct board. I have a 1988-89 L98 that has a steady check engine light. I was going to take the car for a ride a few days ago my idle was high (1400 rpm), the ses light was on and when I put it in gear the car stalls and shuts down. I've used two different code scanners and jumped the terminals and the light will not flash or communicate with any scan tools. I've followed the mitchell, GM,and all data diagnostic flow charts, I've used three new ecms and two new proms and the light will not flash. So I went to a junkyard and picked up a ecm and prom for a 1988 s-10 4cyl plugged it in and the light will flash code 12 only. Has anyone ever heard of this and if so how was this issue remedied. Also this vehicle has no VATS system.

 

First of all, the VATS only prevents starter function. It is a primitive system and has no effect on ECM function. Your new ECM is flashing code 12 which means it is going into diagnostic mode. I would say from this that your old ECM was defective or that you had poor connection which was solved by the ECM R&R. The hich idle and inability to compensate for load could be caused by several things. A few that come to mind are TPS, IAC, or lean condition. Since you have a scanner, look at data for TPS voltage, IAC counts, integrator, BLM, and O2. TPS should be at .5v with the engine at idle. IAC counts should change when the headlights and HVAC blower are turned on.

Let us know what you find.

 

I assume you swapped out the S-10 EPROM for one of your original, or one of the new ones.

 

My statement oncerning the VATS system was incorrect. The VATS is tied into the ECM and allows or prevents injector pulse along with its control of starter engagement. However, if the engine starts and runs, it is unlikely that there is an issue with the VATS system.

 

I used the button and it made me more so Since this topic is related to my problem as well... I cant findout the meaning of my code! it does the reg code12 then flashes once- then 5 times.... I have a 350 tpi and the tps is new. it idles around 2500 when warming up.. then idles around 1k and dips up and down about 100 rpms... it drives fine just i dont want to see that orange light anymore!
sorry for the little hijack

 

Code 15 is CTS signal high. It means your coolant temp sensor is reading high voltage or low coolant temp, causing your engine to want to run rich. This is causing your loping idle. Check out your CTS and replace it or repair the harness as needed. So you know, the CTS is at the front of the intake, next to the thermostat. One black and one yellow wire.