Hello to all, I could really use some opinions as to what my issue might be from: To start from the beginning, I have a 2002 Tahoe 4.8ltr 2WD, auto. It has 101000 miles, and has been running flawlessly since day 1. I recently started to have a "MILD" motor shake (dont think it is a motor mount, all is good under there) and it starts out like this: On a cold start, the motor revs up to 1500rpm (normal) for 30 seconds or so, then back down to 600rpm idle (normal) then after letting the truck idle for about 5 minutes, You can start to see the motor visually shake, which in turn makes the inside of the cab shake. I dont have patience to type out everything that I have done to try to fix the issue, but it is alot, and nothing helped. Im not dumb when it comes to working on these, as back in 2000-2005 I was (newls1) on ls1tech.com with a massive fast H/C/Nitrous 2000 z28, but havent logged in for over 4 years, and I guess I lost my screen name>.... I called a close friend of mine, and he came over and noticed a vacuum leak type of idle, and said 100000+ miles, COULD BE INTAKE MANIFOLD GASKETS. There were no leaks in any of the hoses anywhere that we could see, blah, blah...... I do notice a surge sometimes recently at idle so this does make sense, Do you guys maybe agree? Could you point me to website that has removal instructions for the intake please? i've searched and couldn't find anything. Thanks.

 

mine before i bought it i test drove and the ses light came on like over 60 on the highway and it was an intake gasket.

 

ive seen several intake gaskets leak. take some carb/brake cleaner and run along the intake as its running. that will for sure tell you its a vaccum leak. it does sound like a gasket leaking

 

great info guys, thanks.

 

If you have access to a scanner the intake vacuum leak will show up by looking at desired MAF and actual. The carb clean does not always work with the smalle rleaks with no SES. because the leak starts at the lower edge and is hard to get the cleaner down there. Only check this cold as the leaks tend to go away warm also.

 

What he said. Only the easiest way to do it on a scanner is to look at short term fuel trim. First off, reach under the middle of the intake and take the foam crap out and through it across the yard, if you fog under the intake with some carb cleaner it will show up on fuel trim. Like he said, it is hard to get carb cleaner to work now days, because a very small leak with only sometimes set codes, and cause driveability concerns, but they will show up by watching fuel trim.
I am setting a p0171 now only when I am really getting on it, when I first set the code and read it and watched my FT you can see it in FT, sitting at idle the right bank ft is +1 percent, the left bank is +3 to 4, so the left bank is lean, and the pcm is fueling it 2 to 3 percent more than the right to make the burn right, that is all fuel trim really means.