View Full Version : RPM steadily increasing (93 N*)

06-05-04, 04:28 PM
When i start my 1993 STS, it will idle at about 1-3k RPM, drop it in gear and it goes down to about 1.5k .. Let your foot of the brake and it will steadily gain speed. When you apply the brakes you can feel the transmission downshift harshly.. so i'd say the engine doesnt want to stop. Replaced the Intake manifold gasket and all connecting hoses (was sold as a unit for $120).

Still have to check the ISC motor, TP sensor and any bindings in the accelorator cable. What do you think fella's? Can't be to serious?

Also, It was an intermittent a few weeks ago.. went away (but not completly) until recently, set a P030 -- ISC RPM out of range.

Driving me insane, bad on the brakes and worse on fuel consumption.. gettin' like 13.4 MPG. Aww damn.

06-05-04, 10:10 PM
ISC motor sounds like it has failed.

That is why it cannot correct the idle speed to the correct level and why the code for the idle speed is setting.......

Replace the idle speed control motor. Easy and quick and cheaper than burning the brakes up and using excess gas...and it only takes about 10 minutes to replace it.

While you are in there, clean the throttle body as often described. Unlikely, but possible I guess, that the throttle blade is catching on some deposits in the throttle body if it is REALLY dirty and carboned up. Maybe clean it first...but not likely the direct problem you are having.

Lots in the archives on the ISC ......

06-09-04, 01:06 AM
Well bbob, I wish i could comment on how easy the ISC motor went in but i never had to replace it.

That next day i went to go mess with it, scope it out, see how she was feeling.
Got bored with the linear read of the service manual and decided to release the cruise control servo and do a idle learn reset, using the on-board computer.

Went upstairs to get a glass of tea, came down and fired her up.
She revved up to 1k and slowly dropped down to an all time low of 650!!
Averaging 18+ MPG in the city. awesome.
Quickly did the idle learn procedure to get her set, been running perfect ever since. If she acts up again ill definatly replace the ISC motor.

Now im playing limbo with the idle, how low can she go?
450+ ..