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An update on this problem... I recently had the time to take the intake system apart and reseal it. I put in new upper intake gaskets, inspected that plastic intake good, and sealed over the seams just in case. I put in a new throttle body gasket, new injector O rings... they were hard and crumbled when I took them off but they were all intact when pulled. I cleaned everything, reinspected all the vac lines, clamps hoses ect. All the plugs were clean and the right color, no rich burning or oil ect.
I stuffed a rag in the tailpipe to see if the STFTs would respond, prior to all this work. This had no effect on the STFT at all. My understanding is doing this should show an exhaust leak if there is one by driving up the internal pipe pressure and stopping any sucking of air, and the STFT should reflect the change. If I got that wrong, feel free to correct me... I forget where I read how to do that.
The batt has been disconnected for a long time, so the computer is clear... itll take a while to see if it all fixed it. For now, it seems like its all good. I have idled it a couple times up to op temp, and the LTFTs are under +/-5. If it idles for a long time, the idle starts to go off and the LTFT go up but not past about 12. They come back down when you rev it up. On a couple short spins down the road, it seems to be keeping much more normal trims now.
Its an extra truck here, no time to daily drive it yet.... which will tell the tale. This weekend I'm going to swap out gear to this one and drive the snot out of it for a while.
I'll post an update.
What I found on the plastic intake was some very slight open seams, looks like heat distortion. I packed all the seams with black gasket goo, just to see if it did any good. if my efforts helped but not enough to fix it 100% I might put a new upper intake on it... there could be hairline cracks in it that open when it heats up (distortion).
I'll update when I pass a couple 100 miles of daily beater driving.
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