66cutlass

Please help. I can't seem to get my idle down. I have a 1986 vette. I have replaced several components. I sprayed starter fluid all around intake and it did not change the rpm. I have idled the screw down but I am not sure how far down I can go.

66cutlass

I replaced the air idle sensor, intake gaskets, egr, vac lines, thermostat, wires, plugs, cap, rotor, knock sensor, starter, rear main, u joints, master cylinder, completely rebuilt transmission and new tires. I really would like to drive it.

Cliff Harris

You probably have a vacuum leak, which is usually the cause of a rough or high idle. They can be very subtle and located in places you wouldn't think would be a problem. Some possibilities:

Ruptured vacuum brake booster diaphragm or bad vacuum line to brake booster.
Bad vacuum check valve on the brake booster.
Open/broken/cracked vacuum lines for the cruise control.
Cruise control vacuum brake switch bad.
EGR valve stuck in the open position.
Bad vacuum check valve.
Bad vacuum line where the PCV vacuum line attaches to the intake manifold.
On '85 to '88 cars the cold start injector can have a leaky O-ring or not be mounted correctly.
The vacuum connections to the charcoal canister could have problems.
The canister purge solenoid might be bad. It is normally in the open position and when the ECM energizes it then it closes.

There is a specific procedure for setting the idle speed. Diddling with the screw is not the way to do it. This is the correct procedure:

http://forums.corvetteforum.com/1570563689-post1.html

aklim

I'd get a scanner to see if the idle is too high and adjust the TPS and IAC thru the scanner.

VikingTrad3r

Hey if the OP were to do that, but still had a vac leak, would he still have rough idle or any other downsides to living with a vac leak?

Cheers. VikingTrad3r

aklim

Besides it possibly not running right?

If you don't have things running in spec, it is not a good thing. A scanner will help you see what the ECM sees. Much easier than guesswork to see what is going on. Seen too many people simply throw parts at a car and hope it works.

My intake manifold to base manifold had a leak. It was reading high idle all the time. Scanner confirmed it since the tach is notorious for reading high. See IAC counts were always 0 which tells me that it is getting more air than needed. Turned it in all the way and it still read 0 so I knew something was leaking. Plugged off IAC hole and it still ran and was at 0 counts so we went looking for the leak.

66cutlass

Wow! I set AIC and TPS according to the link above and it made an amazing difference. Idle can go lower once I figure out why engine runs very rich.

aklim

That procedure only works if the car is bone stock. I also have a scanner. Kinda why I don't ever use or advocate that procedure. If it is running rich, it might be a Coolant Temp Sensor and/or dirty injectors that aren't spraying a fine mist. Your injectors are junk anyways. I'd test or just replace the Fuel Pressure Regulator just because it is that old and you are already there if you are doing injectors

You couldn't even give me any of the Multec injectors. They were the first thing to hit the trash can when I got my Vette.

66cutlass

All I know is that it is a Z51 - if that makes a difference?

aklim

I don't think so.

Tim_Ko

I bought an 85 and one of the problems was that it idled high. It had a big giant (1.5" diameter thin gage) return spring to pull the throttle plate closed ... and it still idled high. So apparently the neighborhood mechanic couldn't figure out a fix either. Yeah ... I checked all that other stuff mentioned above and it still idled high - I replaced all the vacuum lines ... still idled high. So, after looking at it, I removed the cruise control unit which has a wire to the throttle thingey. Now it idles and there are less vacuum lines running around in there.

66cutlass

I already removed the cruise control thingy. It still idled high. I believe I can get the idle lower if I can figure out why the car runs a bit rough and smells like gas coming out of exhaust. The first second I start car it smokes one puff then there is no smoke???

aklim

Get sensor readings. It can clue you about what is going on