Please Help!! 1999 Yukon OBS Surging when idling.

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Panner99

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Hope someone can help!!! My 1999 Yukon has a bit of a rough idle. Not too bad, but noticeable. When it gets hot or its hot outside it surges sometimes. The injectors have been replaced last Oct to the MFI injector upgrade, plugs, wires, IAC, and PCV valve all have been changed. I checked for vacuum leak, nothing found. No check engine light either. I'm at a loss.

Would it be MAF? ERG Valve? Crankshaft pos sensor?

I cleaned my EGR Valve the other day. Did not fix the problem.

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skylark

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Two common things vortec, dirty maf and cruddy distributor caps. Occasionally a worn distributor gear.
 

Panner99

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Thank you for the reply. The SUV only has 81000 Miles, would the distributor gear be worn yet???

I also forgot to mention it drives perfect. All this happens at idle.
 
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skylark

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Typically not for distributor gear wear unless nobody changed the oil. Get a can of the maf cleaner and try that first but with a new spider, wires and plugs it rules out most tune up components unless you got a bad one. My money is on the cap.
 

Panner99

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Thank you Skylark. A cap is cheap. I will get one and see.

Spack9. I put in a new idle air valve. It didn't change a thing. This problem is driving me mad. Lol.
 

Panner99

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I actually was going through the invoices from the truck. The Dist cap and rotor were replaced last Sept 2016. So that rules that out. The only tune up things that haven't been changed were the coil and the plug wires.
 

94OldRed

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Have you changed the fuel filter recently? I know my truck was running really poor when I had a clogged one. Might not be directly related, but they're cheap and that might help.
 

Panner99

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Looked into it fuel filter is about 8 months old. I was going through the receipts from the previous owner. Lots have been done. I added some SEAFOAM additive. Seemed to help a bit. Still idles a bit rough. The odd thing is, the truck has a lot of power, and drives perfect. Only issue is at idle.
 

redfishsc

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I would still suspect the IAC, those seem to be iffy little creatures.

The range for the idle seems to be 400 to about 700rpm, which I think are the two idle rpm's for "warm" and "cold" engines. If you have the ability to read the coolant temp via the OBD2 system (which uses a different temp sensor than the dash gauge), you might find that this sensor is failing. I'm taking a wild shot in the dark here. I know my 99 Suburban typically idles at around 700 if cold, 450 if warm, although this varies.

Lately (this week) I've also been having rough idle, but it's been dropping rpm, not as rhythmic as yours either. Twice, it's stuck itself at 1700-1800 rpm idle as well, on a warm engine, in park... .which was a bit worrisome since I was 200 miles from home when it happened, with half the family (including an elderly Mom on oxygen).



Thank you for the reply. The SUV only has 81000 Miles, would the distributor gear be worn yet???

I also forgot to mention it drives perfect. All this happens at idle.

Just out of curiosity, you say that it only has 81,000 miles, but the one in the video has 129+K miles. Not busting your chops or anything, but why the discrepancy?
 
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