Would a faulty PROM or bad tune cause this problem?
11-16-2016, 07:12 AM
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Car: '88 IROC-Z medium orange metallic
Engine: L98
Transmission: 700R4
Axle/Gears: 3.27
Would a faulty PROM or bad tune cause this problem?
I'm going to try and keep this short.
'88 MAF TPI L98 with 7165 ECM.
The issue is a rough, high idle. Cold start is ok, it will idle around 900 in park and drop to 750 in gear. Once it warms up it will sit in the garage and idle just fine. When I take it out for a drive, by the time I get to the first stop sign the idle will be up around 1000-1100 RPM. I've been chasing this problem for weeks now. Myself and two ASE master techs have looked for vacuum leaks and can't find any. Have replaced the MAF, IAC and ECM. I've done the IAC relearn procedure several times. I know the engine has been replaced at some point and I suspect they may have slid an aftermarket cam in it. My question is would a larger cam cause a higher idle? The ECM also has the original Delco PROM in it. Is there a way to tell if it's gone bad? I'm stumped and any help is much appreciated.
'88 MAF TPI L98 with 7165 ECM.
The issue is a rough, high idle. Cold start is ok, it will idle around 900 in park and drop to 750 in gear. Once it warms up it will sit in the garage and idle just fine. When I take it out for a drive, by the time I get to the first stop sign the idle will be up around 1000-1100 RPM. I've been chasing this problem for weeks now. Myself and two ASE master techs have looked for vacuum leaks and can't find any. Have replaced the MAF, IAC and ECM. I've done the IAC relearn procedure several times. I know the engine has been replaced at some point and I suspect they may have slid an aftermarket cam in it. My question is would a larger cam cause a higher idle? The ECM also has the original Delco PROM in it. Is there a way to tell if it's gone bad? I'm stumped and any help is much appreciated.
11-16-2016, 11:03 AM
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Car: check
Engine: check
Transmission: check
Re: Would a faulty PROM or bad tune cause this problem?
To check if the ECM is running from the PROM: at key-on, engine-off observe the SES/CEL light. It should turn on briefly, blink off, then turn on solid. Can repeat the test after 10 seconds of key-off.
The blink off is the important part, that means the ECM is running from the PROM and the PROM is most likely good.
> I've done the IAC relearn procedure several times.
Are you referring to the minimum air setting? This is critical on the MAF TPI engines.
RBob.
The blink off is the important part, that means the ECM is running from the PROM and the PROM is most likely good.
> I've done the IAC relearn procedure several times.
Are you referring to the minimum air setting? This is critical on the MAF TPI engines.
RBob.
