1G idle problem

[91_gst]

My 91 gst has been having an idle problem. After I start it up the rpms go up to 2500 and slowly go down as it warms up like a usual dsm but once I get into neutral from switching gears the idle shoots up to 2500 and stays there til I go back into gear. It ran fine but all of a sudden started doing this. Could this be the iac or just an insane vacuum leak

 

[pauleyman]

Check the throttle cable. Its not possible to idle over 1500 if the throttle position switch is actually closed. This suggest throttle isn't closed. Find out why and/or fix your idle position switch.

 

[91_gst]

I did and its not stuck open. Its only at idle and in neutral so thats why I thought it may be the iac or a very bad vacuum leak

 

[92AWDHX40]

check your isc, and do a boost leak test.

 

[pauleyman]

At the very least your idle position switch needs attention. Does the car have the stock throttle body ground strap?

 

[hotrodssnova]

Like this one.
http://www.dsmtuners.com/attachments/90tbground-jpg.110548/
that strap allows a ground to the sensors on the throttle body. Remember, it is sandwiched between two gaskets, and might not have a good ground. That little switch tells the code if the throttle is open or closed. With out a ground, it appears open to the ecu, and you get unexpected throttling. Also check out the wire to the switch. Iirc, it's green. It has a habit of breaking, especially on older cars like ours.

 

[91_gst]

The motor is getting rebuilt right now but when we get everything back together I will come back with details. Thanks alot guys

 

[mikespenny]

While its all apart, replace the gaskets/orings for the iac, possibly replacing it.
Also, replace the end seals on the throttle body shaft.

 

[91_gst]

Will do