There is not a clear section for this type of issue so I will but it here.

I had some performance and mileage issues that turned out to be plugs and wires related.


Well.........
2 days after I did the plugs, wires, cleaned the MAF and TB sensor I have had a gremlin in Red that is running me crazy.

She starts and idles rock solid, drives as good as she ever has and has plenty of Power to spare

Now for the However,

I get high idle (1500 to 2k RMPs) if I am moving down the road and take her out of gear. when I come to a stop she will drop back to 850.

NOW the odd part, if I push the clutch in it drops to 900 let it back out (still going 30, 60, etc) while still out of gear and it creeps right back to the 1500-2000 range.

Ok, so it acts like a vacuum leak or a tuning issue; but I have made no changes to the tune and it would idle fine out of gear running 10-90mph before (yea, yea... I do a lot of coasting)

ok, no tuning changes that means vacuum leak......
well it would not idle right and would not stop when I push the clutch in UNLESS you guys know of a certain line that would be controlled by some clutch function I could have knocked off.


Things I did during my repairs and since then.

Changed plugs and gapped them
New Duramax wires, no ox wire boots, anti seize on plugs
took off TB cleaned sensors with electronics cleaner
but some no ox grease on the gasket that mates to the TB on the intake too keep it from drying out (I don't know why!!)
Cleaned MAF with same cleaner that I used on TB sensors.

Have pulled the TB looked at the gasket, replaced and tightened again (it almost looks like it is not sealed right on one corner, but I think I am just paranoid)

Anyone shed some light on this for me?
I take myself as a good trouble-shooter and long time shade-tree mechanic, I am lost so far.

 

maybe your not start the car and spray some cleaner in that area and if it idles up you have a leak. or maybe you still have cleaner in that that needs burned off causing it to rev up dont know. def sounds like a leak

 

Mine does the same exact thing and its bone stock except for my catback. It just started doing it one day.

 

Sounds like a vacuum leak...if nothing appears to be obvious, it might be at the back of the manifold. I had one back there where a hose had worked its way off, and it drove me nuts...I found it when I pulled the manifold to swap fuel injectors. Other than that, I'm just as lost as you...but I assure you, there is a logical explanation, even if it isn't right in front of you.