1986 Chevy Celebrity Fast Idle

RODAN99

MEMBER
1986 CHEVROLET CELEBRITY
6 CYL
FWD
AUTOMATIC
50,000 MILES

My car has been idlling fast lately. Does it whether engine is cold or warmed up. The car has been in the family since new in 1986, but, only recently does it get driven a bit more, about 150 miles per week the past year. Prior to that, maybe 3,000 miles a year.
Someone told me to diisconnect the battery for an hour to reset the computer, and this might reset it, to alow it to idle like it should. Will this possible fix it?
If not, is it possible for me to manually adjust the throttle? It is a 2.8 liter V6 with fuel injection. There is no "service engine" light showing a problem.

5 Replies

RASMATAZ

MECHANIC
75,992 POSTS

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.

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Friday, April 24th, 2009 AT 9:22 PM

RODAN99

MEMBER
4 POSTS

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?

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Saturday, April 25th, 2009 AT 4:00 PM

RASMATAZ

MECHANIC
75,992 POSTS

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

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Saturday, April 25th, 2009 AT 6:20 PM

RODAN99

MEMBER
4 POSTS

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?

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Monday, April 27th, 2009 AT 12:03 PM

RASMATAZ