I don't think this is tuning related, which I have stated why. but then again someone may have seen this so I added 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.

 

Check the Air Fuel and see if by cleaning the MAF and such it altered the settings.

 

Hi Stranger! Long time no talk..

You need to IM me some time.

 

I would but I am never on AIM anymore. If you get MSN we can.

 

Do you have a tuning program? If so you need to look at your idle airflow tables. I ran into something like this a while ago. My warm idle airflow was too high and cold was too low. So my idle trims would go way positive while the car was warming up. Then I'd get on the highway and fully warm the car up. After getting off the highway the idle trims are way high on top of the warm idle airflow that is already high. That makes the IAC open more than it needs to when you're in neutral.

 

Any codes? Or DTC's?

 

No tuning issues, that was what I meant... it ran great (but did not want to idle cold due to bad wires and plugs I fixed that)
Then the hanging moving idle started, after I did the plug/wire change.
No codes or DTCs, heck she runs great.


I did some work yesterday, I will know on the way to work in the am.

 

By fixing the plugs and wires you changed the amount of air it needed to idle. The computer still thinks it needs the old amount of air to idle. It may be as simple as just needing to let the car idle for a long period of time after warmed up so it learns the correct long term idle trim. Long term idle trim is very slow to learn, it won't change much just sitting at a stop sign for a few seconds.

Just because you did not change the tune doesn't mean it's not a tuning issue. The fact that the hanging idle goes away when you stop moving confirms that it is a tuning issue. Try letting it learn the idle trims by idling for a few minutes next time.

 

This has nothing to do with this thread sorry for hijacking it, but everytime i look into the PCM section of the board and read some threads it never stops amazing me. I think its kinda cool that the car's Computer can actually "learn" what makes it run properly and adjust...well to an extent anyway. Kinda makes you wonder what the future holds.

 

PMack,
I have done a Idle relearn a few days after it started acting up.

I guess I need to fix my laptop so I can start gettng my HPT working again.... :/