Fresh engine rebuild - RPM is sticking and only increases, surges

The only code I am getting is P0121 Load Monitoring (Air Flow to throttle angle) Fault - Value not Plausible. Fault Present and Static.

When I start up the car, it idles fine, but as soon as I give it a little gas, the rpms increase and stay there even after releasing the pedal. Touch the pedal too hard, and it surges. It went up to 4k RPM and had to shut it off. I was able to clamp the IACV hose and touch the pedal just enough to get to 2500 RPM so I could do the break in. Break in went very smoothly. 30 mins, 195F, 18psi oil (though this seems half as what it should be?), 2500 rpm, clean exhaust, drained oil and looked only slightly darker than new

What I've done
- Live data on the TPS shows it going from 0-70% (WOT) with linear progression, so I believe the TPS is ok?
- Unplugged MAF and IACV, no change.
- The throttle body, IACV, and MAF was thoroughly cleaned before all this, so I can't imagine its sticking, but I'll need to be double check this (the throttle cable fully closes, but I haven't looked inside yet)
- I resetted the adaptive values before the initial startup, so maybe the computer just needs to relearn its shit?
- live data shows Desired Idle RPM is always the same as current RPM. (increases when pedal is touched)

Could it be a vacuum leak? I can't imagine a leak could give the engine enough air to get to 4k rpm? I checked all the vacuum hoses, visually they look good, and used a new intake gasket w/ copper gasket spray.

The u-shaped thingy where the cable attaches does return to normal position. I can't actually see inside the throttle body though, but from memory, I don't see how the flap could be open if the thingy on the outside is fully closed. I've also tried pulling that thingy closed while the engine is running to be sure

edit: thingy = operating lever

D2

Thanks for the tips. Evidence points to the butterfly spring or TPS, but its a little perplexing because the TPS is reporting good data from 0-70% (assuming 70% is correct WOT) and when I put it back together, the flap was working great

The only way I've found to lower the RPM is to clamp off the IACV. With that done, if I apply more pedal, the RPM rises again and cannot be controlled any longer. Have to kill the engine and try again.

Should I try running the engine with the intake tube and MAF disconnected and watch the flap?

Alright its definitely the throttle body spring or maybe the TPS. When I get the rpms up, then go whack the TB with a screwdriver, the rpm starts to return to a nice idle of 680.

squirt said:

Just take the damn intake tube off the TB and see if the butterfly is stuck open. It's one clamp.

Click to expand...

I did check it with the engine off. It's not stuck. I have a cheap tps from rock auto arriving today to rule that out.

With the car off, computer says throttle angle always returns to 0% on its own, but when the engine is running, it only returns to 3-5% until I whack it.

Turned out to be a simple throttle cable adjustment and lubing the return spring. I guess since it is a fresh rebuild I suspected the worst off the bat.

Running great! Tightened the sai tubes and no more tapping.