[2000CAYukon]

I have a 90 GMC K1500 5.7 Auto that had a rough idle in drive. It never stalled but drove me nuts. I eventually figured out that the vacuum hose to the MAP was leaking along with the PCV gromet not sealing. After replacing both the gromet and the vacuum hose. The idle quality greatly improved.

What helped me was using a scanner and watching what was happening when the idle got rough. I could see that the engine was running rich and the ECM was trying to lean it out. My theory was that the PCV valve was not doing it job along with the MAP vacuum hose leak caused it to run rich.

Other things to look at are EGR valve, EGR solenoid and O2 sensor.

//2000CAYukon