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Re: 90 GMC Sierra 1500 350 NEW EVERYTHING idle problem
I have owned my 90 GMC K1500 5.7 700R4 since new. I also had the idle problem you have.
I found that I had 2 vacuum leaks. One was the vacuum hose to the MAP. The other was the PCV gromet in the valve cover. An AC Delco PCV and new PCV gromet made the biggest difference.
It would also help to hook a scan tool up and see what the ECM is seeing from the sensors and what the fuel trims are at. In my case, before the PCV and gromet where replaced, I would see BLM reach 108 (128 is neutral); therefore the ECM was removing fuel and the idle would cycle up and down. I think the vacuum leak at the PCV would allow crankcase gases to build up and fool the ECM to thinking the engine was running rich.
//2000CAYukon
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