2001 Chev Venture - 3.4L DTC PO171 - FIXED

[Tim Martin]

I got this 01 Venture with a 3.4L engine that has 63,000 on it.

Issue is PO171 comes on as soon as engine idles long enough for fuel trims to be above +20 for 6 seconds or more. Cruising down the road there is no problem. I can erase code while cruising - no problem develops until I stop at a light or stop sign, then cel comes on and I got a PO171. What I am wondering is what in the airflow chemistry changes at idle? Fuel pressure is right on the money, vacuum at idle is 19.5.

Puzzling.

[fortknoxx]

8th dig E? these were known for their intake plastic manifold gaskets that expanded and contracted and wouldshift. gm had a few updated ones, last I remember they were using dow's to hold the gasket still.

[Tim Martin]

Eighth digit is E. And yes, I am aware of the plastic intake manifold issue on them. One of GM's light bulb ideas if ya ask me.

[Tim Martin]

Ah............. in checking, this one aint got a plastic intake.

[brianp87]

I would be leaning towards maf sensor

[ricmorin]

Lean at idle and ok at higher rpm's usually indicates a vacuum leak. Throttle bodies leak often on these as well as the intake. MAF's sometimes can trick you into thinking vacuum leak, but more often just are out of range across the board. How's the fuel pressure?

[brianp87]

Maf, vac leak or fuel those are the possibilities.

[Tim Martin]

I want to update on this one.

In checking it out the other night, I found a vacuum cap off on the rear of the intake manifold. This is interesting as another shop recently replaced the intake manifold gaskets. I expect it was left off or came off during the process. But at any rate, the engine runs near perfect with a vacuum cap on the port.

Thanks for all the ideas.