Fast Idle

[mmark2]

A couple of days ago my car started to idle around 1600 rpm, from the 800 rpm that it normally runs. All I've done is put a K&N filter in it, and cut out the front of my filter box. Anyone have an idea what to look for?

 

[lancewest]

GM Mark,

I have the same question for months, on my '93 convertible.

Initially changed the opti-spark distributor and almost immediately noticed the idle @ 11-12 RPM. Every suggestion was taken to heart. Vacuum leak - none found, idle air control valve -replaced, timing - checked OK, its been 90 days, so now I find out the Power Brake Booster (on the '93's its a drum sitting on the firewall behind the master brake cylinder) had a crack in it from the mechanic who worked on it originally to change the distributor, that caused a vacuum leak, which caused the fast idle, but look out, it will cause grey hair trying to isolate it, unless you have a great corvette diagnostic person in your neiborhood.

:confused

 

[69MyWay]

Let's go with the obvious first.

Any chance at all you have a leak between the Mass Air Flow sensor and throttle body? Is the boot on right, clamp loose, or too tight?

Look at your PCV and make sure it is not leaking between the valve and the intake.

Here is how you set the base idle with engine at operating temp:

1. ground the ALDL as if you are going to extract codes and turn the key on. Wait about 20 seconds then unplug the IAC motor on the throttle body.

2. unplug the jumper in the ALDL and start the car with a friend close to you. Let the friend sit in the car, set the e-brake, hold the brake, and put the car in drive (if an auto).

3. Set the idle (you may have to knock the plug out if the idle has never been messed with) to about 550-600 in gear.

4. Shut the car down, plug the IAC back in, start car, and go for a drive. Hold it at 45 mph or above for a few minutes, then at the next red light lite should idle down to the correct spot.

***BEFORE*** I did all this, I would remove the IAC and clean it as well as the passage it goes in. In fact, remove the whole throttle body housing and clean it up as it is sure to be full of carbon and deposits that may cause it to hang up.---then...do the idle reset as noted above.

If idle remains high, reach down and uplug the Mass Air Flow while it is running and see if the idle comes down. It is possible you damaged it while playing with the air intake hose, not enough to set a code...but just enough to throw the low speed air flow reading off.

Good luck!