While rebuilding my throttle body I was cleaning the throttle plate. I noticed when it was fully closed water would not go past the throttle plate until I opened it manually. There is a small amount of wear on the TPS plate where the Idle screw hits it. The plug is still in the adjustment screw so I did not move it.
Is the throttle plate supposed to close that completely? It does not seem to stick but I'm still having problems with Idle around 1500 RPMs unless I blip the throttle.

quote Originally posted by JMTUT: It does not seem to stick but I'm still having problems with Idle around 1500 RPMs unless I blip the throttle.

So... do you want it to idle at 2000 RPM or what?

This isn't some old carburetor. Leave that throttle-stop screw alone. It's not an "idle adjustment" screw. Idle speed is controlled by the IAC valve... not by the TB butterfly.

[This message has been edited by Patrick (edited 01-30-2018).]

Thank you for the response.

I realize the idle adjustment screw is set from the factory and I have no intention of adjusting. I am just asking if wear over 30 years will allow the throttle plate to close too tight thus causing the IAC to open more and compensate. My TPS is not adjustable so everything must be controlled through the ECM. If the throttle plate position has moved due to wear on the idle screw stop, then the assumption of base throttle position has moved.

My question is: How tight does the throttle plate close? Is it supposed to block all air at idle?

quote Originally posted by JMTUT: I am just asking if wear over 30 years will allow the throttle plate to close too tight thus causing the IAC to open more and compensate. My TPS is not adjustable so everything must be controlled through the ECM. If the throttle plate position has moved due to wear on the idle screw stop, then the assumption of base throttle position has moved.

There is a "correct" reading for the TPS (.4-1.25v as seen with a scan tool). If for whatever reason the TPS value needs to be altered, bend the TPS lever.

quote Originally posted by JMTUT: My question is: How tight does the throttle plate close? Is it supposed to block all air at idle?

My experience is that as long as the butterfly is completely closed and not binding, it's fine.

[This message has been edited by Patrick (edited 01-30-2018).]

quote Originally posted by Patrick: So... do you want it to idle at 2000 RPM or what? This isn't some old carburetor. Leave that set screw alone. Idle speed is controlled by the IAC valve... not by the TB butterfly.

Nope.

Proper Idle stop screw adjustment is important and required per FSM. See my Cave, Idle Stop
From factory TBI throttle butterfly is set a little bit open then capped so people leave it alone.

Course idle is set by that screw.
Fine tune idle is then set by the IAC.

Several things happen to F'd the system. Depending just how they're made: (Not just a Fiero problem...)
1. Many mess w/ the screw and cause a lot of problems. Even remove factory caps to prevent tampering. When you see cap is missing then safe bet screw is way out of adjustment.
2. Screw can wear or move over time closing the throttle gap. Spring prevent moving but can happen after 20+ years.
3. Screw tip can dig a hole in the arm on the shaft doing same.
3a. Some screws are on the throttle shaft and dig a hole in the soft aluminum body.
4. Replacement TBI will often need idle screw adjustment.
Often none of these will trip any DTC like 35 Idle Speed Error

Fully close throttle will cause TBI injector problems like can slug the engine w/ too much fuel sitting on the butterfly when you hit the pedal.

If the screw tip has dug a hole then see if you can bend the arm just enough to get a good area.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 01-30-2018).]