05 TB 4.2 throwing P0171 and 172.

[Rizzoj2000]

i have just purchased a 05 trailblazor LT with a 4.2 strait six. The other day while driving on the highway at 65 MPH in cruise, the car began speeeding up and slowing down and began acting like it was running out of fuel. iIt would slow down to about 60 and then the trans would down shift trying to get back up to speed.I would then have to floor the pedal and it would bog and then finally speed up. I also notice that the idle at this point would stay at 1000 RPMS. Then it threw a P0171 code. I changed the MAP due to a suggestion on the site with no difference. Then it will go days totally normal. Last night it started up again. this time it wouldn't idle at all and as I was going down the street the revs pulled up to 4000 with my foot off the pedal almost ramming into the back of a car. i had to throw it in neutral and turn off he key. I cleared the codes and today it started again and it just threw 2 codes, P0171 and P0172. Sorry for the rambling post I just can't think of a shorter way to explain it. Any ideas guys. Thanks, Joe

 

[The_Roadie]

WELCOME!!

Check vacuum leaks and a few other things discussed in this video (I haven't watched the whole thing, but it looks VERY professional and competent.)

https://www.youtube.com/watch?v=AUv01ao4GQ8

 

[Robbabob]

Welcome to the Nation!

That's an excellent video, Roadie! Another prime example of why one shouldn't throw parts at a problem until you've diagnosed the core issue.

 

[Rizzoj2000]

WELCOME!!

Check vacuum leaks and a few other things discussed in this video (I haven't watched the whole thing, but it looks was noteVERY professional and competent.)

https://www.youtube.com/watch?v=AUv01ao4GQ8

Thanks Roadie. I also have a problem with the secondary air check valve. I noticed in the video that it stated that I didn't effect the running of the car. It looks like my acceleration and idle problem be from something else. Any ideas on that. Joe

 

[The_Roadie]

Unless the check valve is stuck open, it won't affect driving behavior. It's only to lower EPA emissions on a cold start.

You didn't share the mileage, but whenever you buy a vehicle without iron-clad proof of its maintenance history, you need to change ALL the fluids. Especially the transfer case which is due every 50K (not 100K) miles.

And the plugs at 100K. Use only Delco 41-103.

And of course, remove and clean the throttle body. It's the miracle $5 cure for a LOT of what ails the I6 engine. Shouldn't even troubleshoot much else until you know the throttle body's clean on the backside.

 

[Rizzoj2000]

Thanks again Roadie. I removed and cleaned the throttle body today. I also put a new air cleaner in. I made sure the ECM was reset and it ran great for about 30 miles and then started up again. I ordered a check valve. I think it is stuck open. The mileage is 80000. We'll see what happens after the check valve is installed.

Unless the check valve is stuck open, it won't affect driving behavior. It's only to lower EPA emissions on a cold start.

You didn't share the mileage, but whenever you buy a vehicle without iron-clad proof of its maintenance history, you need to change ALL the fluids. Especially the transfer case which is due every 50K (not 100K) miles.

And the plugs at 100K. Use only Delco 41-103.

And of course, remove and clean the throttle body. It's the miracle $5 cure for a LOT of what ails the I6 engine. Shouldn't even troubleshoot much else until you know the throttle body's clean on the backside.

 

[IllogicTC]

Thanks again Roadie. I removed and cleaned the throttle body today. I also put a new air cleaner in. I made sure the ECM was reset and it ran great for about 30 miles and then started up again. I ordered a check valve. I think it is stuck open. The mileage is 80000. We'll see what happens after the check valve is installed.

If you're still seeing bad results, could be a loose intake manifold. Happens all the friggin' time. Could be worth taking the torque wrench to it, 89 inch-pounds across the board on all 10 bolts if I remember right.