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Discussion Starter #1
Hi All,

I have a 1994 Camaro Z28 with 98k miles that is having some idle issues and misfires when warm. I have had the car since 80K miles and I didn't have any issues before this. The issues started last summer and I have not been able to diagnose the issue. Once the car warms up to temp after it has been driven for a while, it will start to misfire and the idle starts surging. The car also has some issues starting it usually will crank for 5 seconds or longer before turning over. Other times it will turn over within a second or two even if the engine is warm. The idle surging will usually go from around 800 to 1500. If it isn't surging at idle, the idle will still be very rough and the car shakes a bit.

The misfires happen warm at WOT. They will also happen during light acceleration when the overdrive is active around 2k RPM when cruising about 50 MPH. In this case, it will detonate, then be fine, like the air/fuel ratio isn't right, then it corrects.

Attempts to correct the issue:
-Replaced O2 Sensors
-Replaced ICM
-Replaced Throttle Position Sensor
-Cleaned the MAF

All of the modifications in my signature were added before I purchased the car. I included some data logs of the issues described above, including idle surging, cruising misfire, and WOT misfire. They are tab delimited text files. Let me know what you think. i appreciate the time to look through this data. BTW I am not sure why RPM shows up as 3k or 4k at idle, could that be an indicator of the issue?

Thanks,
 

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Check coolant temp sensor for corrosion; lots of articles about this sensor going bad and causing the symptoms you have.


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Discussion Starter #3
I replaced the coolant temp sensor over the weekend and the problems are still happening. I am thinking about replacing the IAC valve when I get some time.I am worried that might not do anything because I don't think it would cause a misfire while driving. Any other suggestions or advice? Is there any way to tell if the IAC is bad by looking at the counts in the data log?
 
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