1986 Chevy Celebrity Fast Idle

1986 Chevy Celebrity Fast Idle

Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft and a defective idle speed speed control motor/valve stuck in the extended (high idle speed) position/throttle position sensor. Also the throttle plate could be binding in its bore and kinked accelerator cable, coolant temperature sensor might not be operating properly misleading the computer that the engine is still cold and computer throwing fuel at it raising the idle speed.

According to a Haynes manual for the 1986 Celebrity Multiport F.I. 2.8 liter, I should have a " throttle stop screw" which can adjust the minimum idle speed, which is what I want to do ( provided the ECM doesn't adjust the idle )

In the same paragraph, "when the batter is disconnected, part of the ECM memory is erased, which makes it necessary to "reteach" the computer. This is done by thoroughly warming up the engine and operating the vehicle at part throttle, stop and go, and idle conditions."

So, I guess what I'm asking, if the ECM doesn't "reteach" the computer how the engine should idle correctly, ( in my case, idling too fast )
where is the throttle stop screw located, and, if this cannot do it, what can I mechanically adjust to slow down the idle?

Try cleaning out the idle air control valve could be in the extended positon and see what happens.

I've ruled out the " idle speed screw ". It's already ajdusted to where it's not touching the cam arm.

Where would the "air bypass adjustment screw" be located? I have a Multiport FI. Referring to the MAF sensor, is the "air bypass adjustment screw" located on the firewall side of the MAF? I found the "idle speed screw" on the front side of the MAF.

On the MAF, there is a factory plug I have not yet removed, and it is located on the firewall side of the MAF. Could this be where the "air bypass ajustment screw" is located?

Look around the throttle shaft linkage where the accelerator cable hooks up-could be a stopper screw that can open and close the throttle plate