PhantomCS

My '92 SC400 (non TRAC) finally runs. But it runs really fast. Currently idling around 2000-2200 RPM. Pinching off IACV brings it down to around 1500-1600 RPM. Brake cleaner test shows no other vacuum leaks. Forcing throttle body closed will cause the idle to drop, and with enough force (and IACV pinched off) stall. Obviously, the throttle isn't closing all the way. Cleaned the bore with a soft terry cloth and some seafoam (as far as I could get, at least), and no dice. Removed the throttle body and found two issues.

1: Daylight. It's not closing all the way. I know there's supposed to be an ever-so-slight gap, but this is too much.


2: Further evidence that it is not fully closing, but rather binding up like an a-hole is that the linkage isn't even closing far enough to reach the idle/stop screw, which looks to be unmolested based upon the relatively intact yellow paint.


So what causes this? What could be binding the throttle body up? I did some more cleaning after it was removed, using a toothbrush and seafoam, since I could now access the back side of the throttle, and it didn't help. Obviously, carbon buildup isn't the culprit.

PhantomCS

Ordered a new (used) throttle body. Installed it, and now she idles rock steady about 650-750 rpm when warm.

Ali SC3

iTrader: (10)

The tps could be holding it if it is adjusted too far, or there may be another limiter/screw somewhere on the other side of the linkage, haven't had a sc400 throttle body in front of me for a while now.

PhantomCS

TPS wasn’t installed, and the butterfly was binding before it even got to the idle screw

Ali SC3

iTrader: (10)

gotcha, haven't had one do that yet but I would be curious to tear it down. its possible something got loose or warped etc.. or is binding from buildup somehow.
when you twist on it you don't see anything else moving? like maybe on the linkage for the cruise control cable on the other side.
either way sounds like you got it fixed but that is an unusual one.

PhantomCS

It is most certainly unusual. No real buildup inside the old one, after I cleaned it. I soaked it in MMO for a day to loosen up the carbon grime, and took a toothbrush to it. It sparkles, but it still hangs partially open. When I turn the linkage in the direction that should close the throttle, the only thing that moves is the shaft and butterfly plate, closing slightly. The cruise linkage isn't impeding it at all. It's really strange. I'm gonna take the pulleys off of it this weekend maybe and play around with it.