Drive by wire

[anotheridiot]

Well, our burnt Trailblazer just puked. Not the normal PCM fuse, or lighter fuse (yes, it is that crazy that the lighter fuse feeds the b side of the computer. Ended up changing the ignition switch again, it fought and fought but still eventually started where a scanner showed me the Groups coil misfiring and I was able to change it. But now its back to this drive by wire throttle body driving on its own, starts too high an RPM, hesitates, then only goes to 3000 with no low power dummy light on.

I have seen some relearn garbage where you start the car for three minutes, turn it off for 60 seconds, then run it for 3 minutes again, but it sure seems like the gas pedal needs to be calibrated to the throttle body. Has anyone run into this?

This was the gremlin we could not find a few months ago, change an ignition switch, change a neutral safety switch, and it ran ok for a few weeks. But this damned PCM fuse is tied to every damn thing, coils, fuel pump, map sensor, so I over fused it to see what would pop. Groups coil popped, but still did not make this drivable with any confidence.

[SuperBuickGuy]

for the car not to throw a code, the 2 sensors in the pedal and the sensor in the throttle body have to disagree. my suggestion is that you're looking in the wrong place for the problem - hopefully it's a simple as a vacuum leak but it's really unlikely the pedal has anything to do with the issue.

Also look at your IAC valve. That sounds suspiciously like it's failed

[anotheridiot]

From what I read, as the years pass by and the carbon starts to build along the throttle blades, the PCM keeps making adjustments, this is over years and years of time. Put on a new pcm and the PCM does not know that, so it runs like it still has dirty blades. I thought with the Modis there might be some calibration, but there is not. Thats all it is a TPS on the throttle body and basically a TPS on the pedal, right?

[SuperBuickGuy]

From what I read, as the years pass by and the carbon starts to build along the throttle blades, the PCM keeps making adjustments, this is over years and years of time. Put on a new pcm and the PCM does not know that, so it runs like it still has dirty blades. I thought with the Modis there might be some calibration, but there is not. Thats all it is a TPS on the throttle body and basically a TPS on the pedal, right?

true-ish, the computer looks for a +/- value when it starts.... but anything outside of factory parameters will get you a code. What is likely they're talking about is on TBI (for example), you have to adjust the TPS after you set the idle bypass bleed.... your system doesn't have anything of the sort.

but you can actually read where the blades are at with most good scanners. HP tuners is one - you can check what the blade sees. Also, you don't have to recalibrate when you put in a new throttle pedal or throttle body in a stock application - that's only an aftermarket deal (mostly because the computer has to be able to control different manufacturers product).

about the carbon - that's what kills the IAC valve.... pull it off, 'exercise it' but turning the ignition on - if it doesn't move, it's junk. They're a pretty common fail due to carbon build up

and seriously, please take those two screws off that hold the IAC to the throttle body and cycle it .... if I say please, will you save me a lot of typing? you can even test without pulling it off - look at the IAC % number on your scanner. It should move when you turn the key on, go to 30% or so when cold then slowly close as the engine warms up with zero being its number when warm.