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  • Surging or searching for idle

    hey everyone my 90 gl is surging at idle will go from 1500-2000 and back down to 1500 ive ran codes and it came up the O2 sensor is reading rich im not sure what is wrong im doing a smoke test tomorrow to check for leaks around the intake however ive also read that the MAF could be the problem alng with a few other thins ive heard of such as IAC and TPS but i doubt TPS would cause the car to run rich. any help would be great thanks in advance
    1990 gl oversized pistons port polish head full exhaust

  • #2
    Check your coolant level. I had an 89 GL with a slow coolant leak that I was having trouble pinpointing. Every time the coolant got below a certain level, the idle would surge. I know it sounds ridiculous, but once I added coolant, the idle would stop surging.
    2005 Dodge Ram SLT QCSB - Daily Ride
    2010 Ford Flex Limited AWD - Wife Ride
    1974 Mercedes 450SL - It'll move again one day.

    Husband, Father, Cable guy...

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    • #3
      I agree with fast91, it is likely your coolant. when there is an air pocket, it hits the idle air on and off so that is what causes the surging
      1989 pgt: 13.6@111mph slow car
      1990 pgt: fast car

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      • #4
        Ive tried checking the coolant levels already and it hasnt fixed anything. Im not sure if i said it earlier but i ran codes on it and it came out as a code 17 which is O2 sensor reading rich. if that helps any
        1990 gl oversized pistons port polish head full exhaust

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        • #5
          So i did a smoke test today to see if the intake was leaking anywhere and it turns out there was a small leak in one of the vacume lines on top of the throttle body so replaced that line with a new one and checked again then noticed smoke coming from a little part above the egr valve i cant for the life of me figure out what that part is it might be the egr bpv transducer judging off the picture underneath the hood but i looked for that online and nothing came up and after further investigetion on this part i noticed the "lid" comes off and there is a filter like object underneath which makes me believe this might be a breathable part. During the time i did all this i took the maf off and had it soak in a parts cleaning tank in hopes that that would help something. Unfortunatly after all this work i have had no success i guess tomorrow ill try burping the coolant system again but i have very little faith that this will solve the problem as i have tried this several time with no success please if there is anymore information you guys can provide i would greatly appreciate it i have to drive this car 800 miles back home next month and id like it to be running properly when i do
          1990 gl oversized pistons port polish head full exhaust

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          • #6
            Tried burping the coolant system no luck unless there's a trick to it that I don't know about also I did notice after it warms up if I shut the car back off it doesn't like to start back up and it only surges after the car has been running for a few minutes
            1990 gl oversized pistons port polish head full exhaust

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            • #7
              Hey guys really need help any info really
              1990 gl oversized pistons port polish head full exhaust

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              • #8
                I've fought a long, hard battle against crazy idle issues with my 89 LX and won.

                Questions:

                Normal cold start idle should be ~1200 RPM. Yours?

                Does the idle settle down to ~750 once the engine is nice and warm?

                Is the Idle Air Controller (cylinder attached to backside of throttle body) warm to the touch when the idle is surging? The IAC has two small coolant hoses connected to it and should start getting warm rather quickly (2-3 minutes) after cold start if all is working normally, eventually getting too hot to hold.

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