just out of curiousity,whenever the car is completly cold,when i start it up the idling will go to 600 rpm sit there a less then a minute not rough tho,then will go to the perfect idle its supposed to be @ 800 to 900 rpm,after i run the car and its fully warmed,when i turn it off and then start it up again the idling is perfect goes to 900 rpm and stays there.

Now is it normal for the car to go 600 rpm on a cold start up? If no what should i look at. Thank you guys

 

I would suspect the Idle Air Control (IAC) valve sticking. I don't think there are any trouble codes for that part. If you do take it out to clean it, be careful to clean it gently. I think it is easily damaged. Fred or Rob can advise further.

 

Correct - no feedback/code for the IAC motor. Shoebox has a procedure that checks the electrical part of the valve:

http://shbox.com/1/iac2.jpg

The valve can get crudded up. To clean it, do not touch the pintle or try to move it. Hold the valve with the pintle pointing down and use a solvent/soft brush to remove any buildup. Do not let the solvent get into the electrical part (which it would do if the pintle is pointing upward).

You also want to check the coolant temp sensor in the water pump housing. The PCM elevates the cold start idle RPM based on coolant temp. Can be as high as 1,200 RPM when the temp gets down to 0*F.

Shoebox has that check covered as well:

4th Gen LT1 F-body Tech Articles

 

Ironically I got the code 42 today. I been having code 36 since last month and since I stop driving it until my appointment on the 15th of the this month to replace the opti-curse.

All I do is move it for street cleaning, but today after I moved it I try starting it up again to adjust my parking and it fire up but died mins later. Try starting it several times, no start.

So I thought welp it's must had finelly died, plugged the scanner in expecting to see code 16 but unexpectedly code 42 was there.

Which brings me here, now I know lol. Before leaving to work I tried to one of more time to start it and fired up. Probably cause its cold.

My big question is, is the problem with all these opti going out has to do with the roter screws coming loose? Is that the reason why when code 36 is on it will still start and drive? Reason I ask this is because I been observing my car in this state since code 36 appeared and it's seem like a on & off thing. Like you can tell the roter screws are backing out as the car runs.

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Opti 101. DTC 36 is for the high resolution pulse from the optical module. The engine can start and run normally without the high resolution pulse signal. The only effect is a slight loss of spark and injector timing. Probably not enough to notice…. in most cases. I have seen people complain of some roughness accompanying DTC 36. That might be what you are interpreting as loose rotor.

But….. there is DTC 16 for loss of the low resolution pulse from the Opti. But….. there is a catch…. DTC 16 can only set when the PCM detects no low resolution pulses AND can count the high resolution pulses. So it’s possible you lost both signals from the Opti. This has nothing to do with the rotor screws coming loose. If you lose the pulse signals from the Opti the optical module has failed or there’s a wiring problem between the Opti and the PCM.

Quick diagnostic - when the starter is cranking the engine, does the tach needle move up (roughly) 150 to 200 RPM? That would be a sign that the PCM is receiving the Opti low res pulses.

DTC 42 is for the ignition control module - shorted or grounded circuit (or heat soaked ICM). Either the ICM or the wiring, Use Shoebox procedure for checking ICM circuits:

4th Gen LT1 F-body Tech Articles

Helpful hint - since you apparently never set up a “signature”, please include basic info like the year of your car in your posts.

 

Hmm that very interesting. If I'm not suppose to feel the symptoms as much as you said while code 36 is on, maybe there another issue? My car has died while driving in this condition, so automatically I'm assuming it's optispark.

I did the gap mod on the icm awhile back, but seem like somebody that worked on my car in the past took the washers off the icm and place it back on the head the stocking way. I don't know why they did that.

And ever since then I been having starting and idle issue. But that doesn't explain code 36. I doubt code 36 can be triggered by a bad icm.

​​​​​I don't know, I can check tonight and watch the tech as I crank it and see if it does what you said.

 

DTC 36 has absolutely nothing to do with the ICM. It is only set if the high resolution pulse from the Opti is not reaching the PCM, or if the high res signal is replicating the low res signal.

Are you experiencing extremely high ambient temperatures? Could be stressing the ICM and the optical module.

 

I live in San Francisco, so ambient temperatures very. Hottest days only get up to low 80s. It's always pretty cool out here.

I check the wires that lead to the icm and all look good. I never had a icm issue ever, let alone a code. Up until now since it's on the head now.

I'm pretty sure it's fryed, so I just brought a new one and see if that changes.

For the optispark, I brought one off of pretis enterprise. I read good reviews on them.