High Idle Speed on 98 STS

dwhoffman · #1 (**permalink**) 05-11-07, 09:08 PM

Hi all,

Recently my 98 Seville STS has intermittently begun to idle sometimes at about 1500 RPM, and at other times at 2500 RPM. I would say that at least 75% of the time, the idle is normal.

Also, when the high idle occurs, I get the "Service Engine Soon". If I reset the code, it usually comes back and correlated to when I also get the high idle.

Any thoughts on what is causing this?

Thanks,
Doug
San Diego

**Ranger** · #2 (**permalink**) 05-11-07, 09:12 PM

What codes are you getting?

JC316 · #3 (**permalink**) 05-11-07, 10:12 PM

I would say idle speed control motor to be honest. It usually causes stuff like that.

**Ranger** · #4 (**permalink**) 05-11-07, 10:19 PM

I think the '98 uses an IAC valve vs ISC motor to control the idle.

Krashed989 · #5 (**permalink**) 05-11-07, 11:28 PM

Certainly sounds like a big vacuum leak. Whether its from the IAC valve intermittantly going haywire, I'm unsure without the codes.

JC316 · #6 (**permalink**) 05-12-07, 12:48 AM

Quote:

Originally Posted by Ranger

I think the '98 uses an IAC valve vs ISC motor to control the idle.

Bah, I just got used to the idea of the idle speed control motor, then they go back to the idle air control. Either way, it could still be that. Mom's towncar acted the same way when it was messing up.