Not sure if any one can help me out or not on this. I am asking for a friend. He has a 2002 3/4 ton silverado with the 6.0 LQ9(i think). It has a rough idle(sounds like it wants to stall out)after he did the free mods to it. Those being: TB coolant bypass, EGR tube was cut out of intake path, he thinks he cut it too short. Not sure if that could be a problem or not. Lastly, he descreened the Mass Air sensor. would any of those cause a rough idle?? we even increased the idle with the adjuster screw, and its still rough. We don't have a scan tool for it, so that will be next on the list. The Check engine light isn't on, but I said to scan it anyway. Thanks for any help in advance.

 

did he mess up the seal on the EGR tube? allowing air into the engine unmetered by the MAF?

exhaust leak?

recheck all the sensors too.

and i didn't think the screw was the proper way to adjust idle, that i had to be done in the computer.

 

thanks for the ideas teke. He said he used a screw on the TB to get it to idle higher, kinda like holding your foot on the gas a little bit. I never thought of the seal on the egr leaking. No exhaust leaks, and I'll double check the sensors and their connectors.

 

Adjusting the idle by the screw on the TB isn't the proper way IMO ... that's pretty much pre-set from the factory, and the IAC should take care of the idle ... adjusting the TB is just "faking" a higher idle, but it's not really the true "idle".

De-screening the MAF "shouldn't" cause a problem, but if your friend damaged one of the wires of the MAF, then he could have wrecked it and it's giving bad readings now (that's a likely cause, IMO).

I'm don't know much about the EGR circuit since my car doesn't have an EGR, but what TEKE said could be very true ... the unmetered air could be tricking the motor into thinking it has a vacuum leak or something?

JMO, but I've never been a real fan of some of those little "free mods" like that. Sure, I did the free "ram air" on my car, but that's pretty simple and straight forward, and it doesn't mess with any of the computer related devices (such as the MAF). I'd rather leave those things alone and get the bigger mods that make CONSIDERABLE differences like headers.

 

He actually has an LQ4, the LQ9 was only available in the Escalade at that time. Chances are it is the seal for the EGR tube. I would highly advise on not removing the screen from the MAF, as it will run leaner due to not reading the correct amount of air entering the engine. If the MAF sensor was damaged, it will throw an error code and put the truck in Speed Density mode. Also, by adjusting the idle with the idle screw, it may throw a "High Idle" code, set it back to stock.

I use HPTuners to scan and tune my 2002 1500HD 4x4, he should look into it.