Howdy! I have a 09 H3T giving me some problems. I have exhausted almost every avenue. I got a lean code p0171and started chasing down the problem which has opened up a can of worms. I've replaced the secondary air check valve, MAP sensor, cleaned throttle body, combed over wires (all good), smoke tested for leaks (none), cleaned the MAF and did a full tune-up including coils/plugs. Nothing has cured the rough idle, hard start, excessive gas consumption along with a strong gas smell from exhaust.

Now here is the weird stuff, I replaced the MAF sensor with a new to see what would happen and the truck wouldn't even stay running and threw a traction control light! I put the old back on and it now runs and the traction control light went away. When I did the tune-up the engine acted like it was having a heat attack before it mellowed out. When I changed the MAP sensor and cleared the code it ran great for about 4 miles and boom back to the same issues.

I am starting to think it's a PCM/ECU issue. Any help would be much appreciated.

 

"Tune up"? Do you have the OEM Intake? If so, check the hose under the resonator to the vacuum port at the back of the engine. If cracked/loose, you need to replace.

Here is THE Thread to cure a rough I5 idle, run down the list and check those Intake Manifold fasteners. Acts like it wants to stall/rough idle -No CEL -What To Do:

 

Thank you for the reply Doc. You touched on it, OEM intake! I had done a full tune-up, secondary air check valve, all air sensors, vacuum test, smoke test for leaks and even pressure checked the cat. It came down to an after market open air intake. It's was tripping out the MAF sensor and causing a lean condition. I had to find a OEM intake system as I bought it this way. I am new to the L5's and hummer in general. Loving my H3T though.

 

You can add an aftermarket "closed" system Intake to the factory Air Filter box and have zero issues.