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Re: Idles high after going from park to gear and back.
The more I re-read your first post, which is well written and covers the topic well (I don't know how I missed so much when I made my first reply) the more curious I am becoming. You even replaced the ECM already. If you can use WinALDL to capture all the data idling slow and idling fast and post the data, and post it, I would surely look it over.
I went looking for specifications for your truck. I don't have a 1989 manual but I do have a copy of the 1988 fuel & emissions manual.
Specifications for a 1988 7.4L with an automatic trans:
The minimum idle speed (stop Screw) is 700 + or – 25 rpm IN DRIVE with a warm engine and all accessories off
The controlled idle speed is 750 in drive – warm engine & all accessories off
The IAC count spec is 5 to 30
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For those of you that are wondering why you are not getting replies to your thread:
Did you give the model, year, engine, fuel system type, and transmission information?
If it is modified from what came stock from the factory, let us know that too.
Last edited by ChevyTech; 03-18-2022 at 12:09 PM.
Reason: Add more
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