1990 SE "crazy Ivan" idel

[teamlorenz]

My 90 SE seems to start up fine one minute and the next time i start it up it will have a eratic idel going from 1,000 RPM to 3,000 RPM back and forth, oviously computer related has anyone had this problem before.
Chris

[Dr.Hess]

Make sure the throttle jacking stuff is all OK. Vacuum line going to it from the controller relay type thing in the engine compartment relay box. Also, check the exhaust back pressure valve thingie. Between the cat and the muffler. Tech tip: Get you some safety wire and wire the thing open (pulled).

Dr.Hess

[greezmunky]

this is usually caused by a vac leak that keeps the fuel pressure regulator from seeing proper vac at idle. check the obvious things (vac lines) then move on to more advanced issues like gasket leaks.

[zeddie]

I had an erratic idle last year and I sorted it by finding that a sensor type - valve - connection was loose, it's near to the oil cap and is held in place with 2 allen bolts, check that one out. I found one of the bolts missing and one was loose!
Geoff.

[Paula&Marcus]

Hi All,
You idle problems may also be IAC-related (=Idle Air Control Valve). Best way to check this is by using Freescan. Should be around 20-40 counts when the engine is fully warmed up. If its too low you might have a parasitic air leak somewhere. If its too high you should think about readjusting the minimum air rate screw.

Cheers
Marcus (www.PUKesprit.de)

[zeddie]

What Marcus says is of course dead on - when I had the problem the Freescan came up with the idle valve thing but as I said it turned out to be something loose. I can't remember the name of the piece, but looking from the rear pass side towards the oil cap it just there on the left, held in by 2 allen bolts.
Geoff.

[teamlorenz]

thanks for the great info.
Makes since, I used to race a C sports racer in SCCA with a olds quad 4 and had the same problem and it was always the air-idel control.
thanks
Chris