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Have been absolutely fighting with this 2004 D2. Got the misfires sorted, a new MAF, new upstream o2's, plugs, wires, coils, and new plenum gasket.
Drove it to work today, and have a pending set of codes, as the title suggests. P1171 and p1174.
I spent the better part of an hour looking for vacuum leaks somewhere, just using the old can of brake cleaner and seeing if it idles up. It was Inconclusive.
Unless anyone has any suggestions, I may just break down and take it to a shop for a smoke test. I can't think of anything else that would be the problem at this point, and I have verified that the new sensors are good, as I watch the values in live data, and they are all in spec. O2 sensors and MAF are functioning properly it seems. Good voltage, it goes up and down when it should, etc.
Perhaps of additional noteworthiness, is my short term fuel trims on both banks are full tilt 25%.
There are some good videos on making your own smoke machine for cheap. I’ve ordered parts to make one but other priorities have gotten in the way for me to put it together.
Vacuum leak sounds like a good place to start looking. 25% sounds like more than a pending code. Is it running in closed loop?
Full tilt STFTs at idle (when vacuum is max), then returning closer to normal while accelerating to get on the highway or up an incline (when vacuum is min) do indicate a vacuum leak. Maybe try blocking off the charcoal canister, if that solenoid has failed open it looks like a vacuum leak.
Did you remove the baffle in the valve cover? Recommend you do the pcv mod regardless of other issues. I can almost guarantee your vacuum leak is a hose- 90% chance. Injector orings really only other possibility assuming yor don't have a wire or folded gasket causing the upper intake to not be sealing
You don't need to buy or build a smoke machine. I performed a smoke test many years ago on a friend's '04 DII using a rubber glove to cover the entrance to the throttle body (after the air intake tube was disconnected), a length of black tubing connected to the port at the other end of the upper intake where the SAI system connects, and a cigar.
It worked great, although after this many years I don't recall where the leak was that we found.