ls1z4me

iTrader: (12)

I have recently purchased a used 2001 Suburban 2500 LT with 68K miles. Is 2WD and e1quiped with e LQ4 6.0L engine with a digital throttle (throttle by wire) body. While idling the engine surges from 350 – 550 RPM, and the throttle position is fluctuating between 6%-8%. This condition is more apparent engine start up and during parking lot maneuvers. Off idle drivability seems normal. There are no PCM codes active or stored. While stopped in gear the less noticeable, yet the RPM of the engines is still only 500-450.

The following has been performed:

• New Battery
• Cleaned Throttle Body and checked for sticking
• Looked for vacuum leaks and check the intake bellows for cracks or damage.
• New Fuel filter
• Check fuel pressure regulator for leaks.

Only mods that I can tell is the last owner has a cat back system put on. Not a name brand system, just looks like they made into a true duel set up.


Any advice or suggestions on my problem well be appreciated.


Thanks,

Josh

NOSjohn

iTrader: (9)

Check the IAC for plunger depth. Should be 2 bolts, pull it out and look at the plunger. If I recall, if it's more than 1/2 inch out, it's bad. Erratic idling is caused by a few things but this is an easy check. It could also be: bad MAF, dirty fuel inj., bad TPS, etc.

Your 'burb is drive by wire throttle? Weird...

ls1z4me

iTrader: (12)

Thanks for the info. Since the burb came with traction control, you get the drive by wire throttle (so I think). There is not an IAC on this style TB. All idle air is controlled by the throttle itself.

Ill check into the other items mentioned.

NOSjohn

iTrader: (9)

Hmm, yep...I thought that was kinda unique.

ls1z4me

iTrader: (12)

Got a tip from a GM Service Tech who thinks I may need to have the computer updated. He says he downloads the updates to the Tech2 and then uploades them to the truck.

Anyone else had this done?

Gunner

Does it have a K&N air filter? If it does the previous owners may have over oiled it and oil has built up on the MAF sensor, like NOSJohn said, try cleaning the MAF.

ls1z4me

iTrader: (12)

It still has the factory style filter in it, but I was thinking on switching to a Farm Air Hog.

Are the oil charged filters bad for the trucks because the MAF is so close to the filter?

What it the recommend way of cleaning them?

I have read that a Q-tip dipped in Acetone works well as well as CRC QD Electronic Cleaner. One guy said he used windex and a q-tip.

ls1z4me

iTrader: (12)

The problem seems to be solved. I took it to my pal who is a GM tech and he updated the PCM using the tech2 tool. Took about 10 min total to download the new module from GM and upload to my PCM through the ALDL, and the idle is much better. From what I can tell this loaded the latest engine calibration on the PCM which must had some improvements for idle control on the electric throttles.

Thanks you guys for the input that was posted on the thread