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I’ve done the same thing in the past. However, I found that, although it can quiet things down and remove symptoms like some minor leaks, it ultimately will accelerate engine wear. Consider, the heavier oil takes longer to circulate than the intended weight oil. You might buy some time with it, but I would plan to deal with the rear main seal before too much longer.
I would focus on your primary problem to start with and worry about the shifting issue later. It may actually be the same root cause.
Now, out of everything you’ve written, the readings in general seem odd. If this were my car, I would start with your current readings and compare against what is standard for your car, or in general. The other thing that bothers me is getting -20 fuel trim but having a rich condition regardless of that. It seems opposite to what would be expected.
What was your fuel pressure reading? You said you confirmed that the regulator is working, but, are the pressure readings within spec?
When was your timing belt last changed? Maybe feel the upper cover with your hand for any vibration, but it’s tough to check the lower cover that way.
Also, you might consider investing in an automotive stethoscope, it really helps localize engine noises.
Today, I cleared the ECU by disconnecting the battery, then holding the brake pedal for 30 sec., drove it for a while, but no change in the condition.
Then, finally, with no other ideas, I decided to “tamper with the idle set screw” in the throttle body. Now, I understand this is set at the factory, and should never be adjusted, according to many sources out there, but a thought occurred to me; It’s a working theory, really, but if the set screw is configured at the factory, for a specific volumetric displacement of the stock engine, then perhaps changing that displacement (as with my case, boring 0.020″ over) necessitates an adjustment in the set screw.
So, I put it in diagnostic mode (where it didn’t run initially) then backed the set screw out a few turns, started it up, then fine-tuned the set screw until I reached 750rpm. At this point, though still a bit unsteady, it holds a decent idle and no longer stalls.
I’m not sure if this was the correct fix or not, but it was the only option left – if anyone knows anything further about these idle set screws, perhaps you can advise if my reasoning is correct – that I should actually change it when the engine displacement is changed like this.
Just a thought, but you might try a vacuum gauge test to 100% confirm there’s not some hidden, hard to find vacuum leak, or perhaps a stuck EGR issue or something. And, watch for a fluctuating needle which might indicate intake valve issues. If I take you literally, the truck was running fine until your paint work, then suddenly stopped? If that’s true, then it’s probably not due to engine fatigue, otherwise I’d recommend a compression test. But it might be good to do anyway, as a matter of course.
If it were me, I’d buy a scantool, then watch various sensor readings while stopped as a baseline for engine idle, then have someone else drive while you watch the sensor readings on the scantool, get it up to speed and observe the same sensor readings when the symptoms occur. Compare against baseline for things like MAF reading, TPS, your various O2 sensors, etc.
As thousands of shade-tree mechanics have said before me, a scantool / proper diagnosis is going to be a lot cheaper than replacing parts by guessing. They are really very easy to use, and something great to have on the shelf when needed.
After posting, this afternoon I did the following:
– SeaFoam thru the TB boot, + gas treatment in my half-tank. It belched out a LOT of smoke, but no change in throttle-stall condition.
– The rebuilt engine is still not broken in, so I drove 40 miles on the freeway, alternating WOT and closed throttle (to the annoyance of all the other drivers on the freeway, sorry fellas!) Total miles on the engine so far: probably 50. (It runs fantastic on the freeway, fwiw)
– Compression-check after driving: 122, 120, 115, 123But alas, it still stalls.
Perhaps this could be related to the ECU re-learning things post-rebuild? I thought I had cleared it by having the battery detached during the rebuild process. In any case, I wouldn’t think it would take this long to re-learn if that were the case. But maybe I’m wrong…