Problem solved, had to replace upper plenum.
Check out my smoke test if you like.
Hey I have an issue and based on my search most have the same type of high idling issue on older TBI models. Just had my new engine Dyno tuned with the 0411 PCM swap. Getting 6-10mpg. I have replaced the MPFI Spyder assembly, new IAC TPS, new prndl switch on tranny and still it idled high in gear and especially going down hill with brakes on. I'm at a loss. Even the guys tuning it at Hawks have no clue because everything is programmed correctly and they thought it might be the PRNDL switch on the side of the 4l60e. So swapped it out and adjusted to the best of my knowledge, I mean it starts in park and neutral and the indicator light is in correct spot on dash, so don't know of anything else I could do to the switch based on everything online and books I've read. The truck will idle on it's own up hill at 30mph at 1500rpms. Then when you come to a complete stop and after a few seconds it kind hard drops the rpms down to 750-800 like it should. It will not drop at all coasting. It stays idling around 1200-1500 on it's own free will. I've read modify the TPS plunger with a piece of fuel hose or just put a toggle switch in the IAC A wire and cut it off after it reaches operation Temp and then turn it back on at start up. I can't afford to take it in to nobody else after spending $2100 getting the thing tuned properly. Had 2 idiots charge me for a tune and put 98 tune for my 97 in a 2001 PCM. It has the correct 2001 tune now plus the adjustments for this HP 74 ATK engine. I am going to also attempt the poor man's cigar smoke pump machine to check for intake leaks. I had issues before because the sorry mechanic who installed everything didn't torque anything properly and damaged the injectors and the assembly seal. All of that has been fixed and spraying brake cleaner doesn't stall engine, but that doesn't mean anything when engine is actually under a load in gear. So gonna try that and maybe replace upper plenum for the 3rd time. Anyway I would appreciate any info and ideas to fix my problem and if anyone knows about the IAC on a toggle switch and if it works I would appreciate the assistance and letting me know.
Check out my smoke test if you like.
New video by TSALI PACE
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