I have an 85 2.5 Fiero. It idles smoothly but when driving the RPMs usually don't return to idle when the clutch in pushed in. If I kick the accellerator it will drop back down to normal idle. It seems like the cable or linkage may be sticking. Possibly the return spring being too weak. Before I start messing with the mechanical linkage, I was wondering if there could be an electrical issue here. I've replaced the throttle position sensor and checked for vacuum leaks. The problem seems to get worse when the engine is at operating temp. Any ideas would be appreciated.

Following because I have the exact same issue 85 2.5. Mine has two springs on the throttle so I assume the PO tried to increase the tension on the cable. I've even let out on the clutch without pressing the accelerator and it still does the same thing. Idles about 900 but goes up to 1100-1200 unless I blip the throttle.

Neither one of you has mentioned checking the operation of the IAC.... and/or whether you've thoroughly cleaned out the seat and air passage area of the IAC.

I've completely rebuilt my throttle body, cleaned the IAC and EGR passages and replaced the IAC with a new one. I suspect I may have a slight leak at the intake manifold gasket but haven't found the time/energy to replace the gasket.

The throttle body was cleaned, the IAC and TPS was replaced, as was all vac hoses and the PCV valve. Can't detect any vac leaks. The idle is steady (though a bit high at around 900 rmp). Overall, runs well at idle, you just need to blip the pedal to return to normal idle.

ECM may keep Idle high when you do this.
ECM goes by engine temp etc to set idle at any time.
For stick cars often idle a bit high to prevent stalling then back down a bit later.

Can be Vacuum leaks too. See my Cave, Vac Leaks

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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

Update. Ogre, thanks for the link on vac leaks. I checked the vapor recovery canister and the large line (the one below the control line) would not hold a vac. I replaced the canister with a working one from an 86 GT at a u-pick yard and it seems to have resolved the issue. It still idles a bit high (1000 rpm at operating temp), so there may still be another vac leak, but at least now it is drivable. Thanks for the help.

1000 rpm on the Fiero Tach is within the usual margin of error.