90 L98 idle speed adjustment

[wedgeheaded]

I recently bought a 90 vert and it seems to me that it idles too fast. I've done a few google searches and found info on adjusting min speed but it's only applicable through 89. There has to be a way to slow it down. Anybody been here done this?

 

[Hib Halverson]

I recently bought a 90 vert and it seems to me that it idles too fast. I've done a few google searches and found info on adjusting min speed but it's only applicable through 89. There has to be a way to slow it down. Anybody been here done this?

Idle speed is computer controlled. Do not attempt to alter idle speed by mechanical means.

It true that the min. air adjustment doesn't apply to a 90 but, the throttle body still has an idle stop screw. It's not uncommon on a car that old to find that someone has screwed it up by trying to idle with the stop screw. If that's the case, you'll either have to replace the TB or try the min. air adjustment for an older model.

Otherwise reasons why it might idle too fast...

1) Problem with the throttle cable
2) Problem with the throttle body.
3) Vacuum leak
4) faulty TPS
5) faulty IAC
6) Incorrect calibration.

The Factory Service Manual has instructions on how to troubleshoot an idle problem along with information on how to fix it.

You can get FSMs from CAC sponsor, Zip Products. That's where I get mine.

 

[wedgeheaded]

The silver plug is still in place on the LH side of the TB. You don't how bad I wanted to knock it out and adjust that screw. Glad I asked first. I had read that a dirty TB might cause it. It runs great so I doubt it's a vac. leak. I'll clean the TB and see what happens. Then I'll move on to the TPS replacement.

 

[Vettelt193]

What does 'seems' mean? what is the idle at? auto or manual? if auto, what is it in gear and in park?

 

[wedgeheaded]

What does 'seems' mean? what is the idle at? auto or manual? if auto, what is it in gear and in park?

It sounds like it's too fast, almost like it's on fast idle on a carb. The tac needs the 90 tac repair so it's no real help. it's auto.

 

[G Winter]

Make sure you check it with a scanner or hook another tach to it, the tachs are notorious for showing to fast. I always thought mine idled to fast both because
of what it sounded like and the tach. scanner says otherwise.

 

[Vettelt193]

Get a scanner and check it first. It should be 650 I think, from memory, so don't hold me to it. If it's high but runs well otherwise my gut says you have a vac. leak. They are the most common reason for a high idle.