Fast Engine Idle

[grose67]

I did a search and saw some old posts but nothing that really helped fix anything. I had to replace the intake gasket on my 98 5.7 a couple of weeks ago. Ever since putting it back together, I have had an issue with the engine idleing fast. I do not show any codes that have tripped the cel. When I pull up to a stop sign, it takes the engine like 5-8 seconds to idle down. When in park, the idle is high and every once in awhile it will rev up to 1200 rpms then come back down. I have noticed that the gas mileage totally sucks right now as well. The EGR seems to be working fine. I took it off and cleaned it real well. There wasnt much carbon in it. The truck ran like a raped ape before the gasket went.

[nickvrebel]

double check all of your vacuum connections.

[grose67]

Still trying to figure it out.

[studibel]

I have had similar issues with fast idle that I can't seem to fix. I have replaced the EGR valve as it was obviously leaking vacuum...could hear it whistling and can stop the sound by pressing in the diaphragm. Also replaced the Idle Air valve...nothing helps. Even after replacing the EGR, i have the exact same whistle/chirping of the EGR valve mostly when you pull up to a stop or at idle. Under load, the noise stops. I'm wondering if I replace the EGR solenoid? Let me know what you find out. I think it is a vacuum leak somewhere telling the ECM to idle up, but I can't find a leak and can't make the EGR quit whistling/chirping.

Stu

 

 

[grose67]

I spent some time tonight doing extensive recalibration of the icm. (I took it off and fiddled with it.....)I plugged it in while I had it out and turned it one way and then the other while the engine reved up and down. When I put it back on, it seemed to work ok and the truck idles down as it should. I am not sure exactly what I did though!