Please Help!! 1999 Yukon OBS Surging when idling.

[Panner99]

I have a scanner. Mac Tools ET 97. I will have to look and see what it is capable of doing. Plugs are new. not sure the brand.

 

[big_mike]

I'm chasing the same issue but mine Sometimes surges while in gear as well. So much so that if your at a stoplight and it starts it'll try to push through the brakes. But if I give it a couple hundred rpm rev and hold it steady it stops surging.

I have replaced plugs, wires, cap, rotor, iac, maf, tps and now I'm about to try a brake switch cause it has also developed what feels like a bucking I suspect is either a failing torque converter or the converter randomly locking/unlocking. Supposedly the brake switch controls tc lockup and some have had this issue if that switch fails. Worth a try for the cost on that issue.

 

[tomb]

The reason I suggest a scanner for a surge is because it may show one bank causing the issue. If the overall fuel trim correction on one bank is over 10% it indicates an issue.

1)If the IAC is completely disconnected does it surge? (A/C off) If no,
2)What inputs to the PCM support idle?
3) How can each of these inputs be tested and eliminated as a suspect?

4)If it surges while disconnected, it must be a physical issue like vacuum or fuel injector leak or something else.

If Im off base, feel free to educate me..

 

[Panner99]

I can only get it to surge if it is really hot out and I have drove for 20 min or more. It will just have a rough idle normally. Should I first disconnect the IAC and drive for a bit and see what happens??

 

[tomb]

Man that sure sounds like a defective new plug. A rough idle is a clue you should chase. It doesnt cost anything to report back what the long and short term fuel trims are for each bank. (At idle after warmed up)
While your at it, say after a 20 minute drive, scan the real time data. Trims, coolant temp, intake temp, report back.

 

[98chevy2500SS]

Spark plugs are a huge problem in these Vortecs. Happened to me. You need to have the good kind, not the cheap ones. I took a plug from my parts Vortec, was a good plug, popped that in mine, engine ran like brand new.

 

[tomb]

I believe 5.7's idle at 600 rpm in drive? Curious what your reading?

 

[Panner99]

Thanks Tomb. I have been busy. Havent had time to scan. My idle is about 550-600. Plugs huh?? I need to look at what the previous owner put in it. Have all the receipts. A lot of things where serviced. I will try and get some reports this weekend.

 

[Yukon squared]

I found the throttle position sensor was making the lurch you feel most likely. And a little is normal I believe.