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Thread: 90 C1500 stalls at idle

  1. #1
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    90 C1500 stalls at idle

    Truck will stall at idle just sitting there and will be hard to start untill you let it sit a while 60 seconds. Worse when hot. Worse when A/C is on. If you turn the wheel fast it stalls. If you put your foot on the brake and keep the idle up it won't stall. Has 326,000 miles on it. Can't figure why it stalls. Replaced Fuel pump and filter no change. When it's idleing it purrs like a kitten. When floored it runs great. No misses or hesitation. Pulls a 7,000 lb trailer perfectly.

  2. #2
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    75K30's Avatar
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    Welcome to the site:

    Sounds like you have a small vacuum leak.

  3. #3
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    yup or ignition problems. check the timing. does it blow black smoke while idling?

  4. #4
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    Timing perfect. Engine is always strong and idles smooth. Just cuts off while sitting there or the A/C cycling. It's like it won't up the idle under small load.

  5. #5
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    Flooded it with carb cleaner. only stalled when sprayed directly into throttle body. Changed the IAC valve. Ran with high Idle for a little while till it was up to temp. Now does the same thing.

  6. #6
    Senior Member 1500cheyenne96's Avatar
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    I would suggest a bad or plugged EGR valve tyr tapping on the EGR lightly with a hammer to see if that helps if not unplug the egr when warm and cold to see it that helps . Also a vacuum leak is a very real possibility did you also spray the booster line with carb cleaner?
    THEY DON'T BUILD THEM TO BE EASY TO WORK ON THEY BUILD THEM TO WORK
    "The Kamikaze"

  7. #7
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    Stuck or leaky EGR, or your vacuum leak is at the brake booster.
    Flooding the engine with carb cleaner is a good start, but vacuum sources are in several places, and the most common and most overlooked area is the brake booster.
    Also make sure that the PCv is functional, and not another small source of a leak.

  8. #8
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    Thanks guys I did spray the brake booster and all the lines. I did change the EGR valve about 100k miles ago when I started getting a check engine light (egr valve) and the light never came back on. It is a cheapo Autozone one though. Now it still idles smooth but I can turn the wheel right or left and it will die under the ps pump load. It's like it just can't give enough rpms fast enough or not at all.

  9. #9
    Senior Member zombie1969's Avatar
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    You sure the iac is working?You replaced it but does it work?It should open and close as needed to maintain the proper idle.You didnt say what its idling at.You have a tac?You have a lot of miles so ajusting the base idle manualy may be needed and reajust the tps if needed.Other than a scan tool Im not sure how to but you can vary the idle up and down through the computer to check it the system is funtional and see if various inputs like the ac kicking on and power assist are being seen.

  10. #10
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    I don't have a tac but it does seem to idle kinda low. WHen I first put the IAC in it idled high then after I drove it a little it went back down.

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