Check Engine light

diamondred · December 11, 2016

Gonna get right to the point by stating the facts that I do know. I have a 2001 Tahoe with a 5.3 Vortec with 165k miles. Check engine light has been coming on the past four winters. It started out a temperatures <10 degrees, and now has gradually gotten worse to <35 degrees. Same codes every time, P0171, P0174, and P0300, Lean bank 1 and 2, and random misfire. Most noticeable is rough idle, the colder it gets, the worse it is. After reaching operating temperature, it idles smooth, with plenty of power and never misses a lick. Last winter fuel pump, filter, and all lines from tank to manifold was replaced.( Due to pump quit working) Also plugs and wires was replaced. After asking around, and doing a little research, I was hoping for an easy fix by replacing the MAF unit, which also contains the IAT sensor. I have to tell ya...it didn't help.

Thank you for the add, and any help you can provide.

txab · December 11, 2016

If I read correctly it happens when cold and goes away after warming up? I'd look into intake gaskets

diamondred · December 11, 2016

If I read correctly it happens when cold and goes away after warming up? I'd look into intake gaskets

I was afraid someone was going to say that. Actually entertained that thought last Spring, but after the climate starts warming up and it stops doing it, one seems to forget the problems.

diamondred · December 12, 2016

For the ones that have done the intake gasket replacements, what kind is he best to use?

davester · December 12, 2016

I believe I used FelPro when I did mine about 2 years ago and they seem to be working fine.

Brapete · December 13, 2016

As I understand it, the throttle body has a lot to do with it. Make sure it's clean and the butterfly is clean as well. If it's not clean the cold makes it worse. Only use throttle body cleaner nothing else. I just did it on my Sierra and my sons cobalt. Both start and run 100% better

diamondred · December 16, 2016

Using a bluetooth plug-in and my android for my diagnostic center, I can't find the EGR position sensor gauge, I could check the position using a meter, I believe it's the tan wire with relationship to ground. If the EGR is being held open by debris, that would cause rough idle right?

diamondred · December 16, 2016

As I understand it, the throttle body has a lot to do with it. Make sure it's clean and the butterfly is clean as well. If it's not clean the cold makes it worse. Only use throttle body cleaner nothing else. I just did it on my Sierra and my sons cobalt. Both start and run 100% better

Thank you for your input. Cleaning is always a good idea, but sometimes not as productive as we hope. My throttle has the butterfly that you speak of, but also has a separate idle circuit. At idle, the butterfly in this throttle body should be at 100% closed.