ZJ_flexxxer Posted November 9, 2012 Share Posted November 9, 2012 ok so i'm running out of options and would like some opinions from some fellow 2.5 mj guys. when i bought my mj it ran smoothly with no problems then one day started idling a little high but went away shortly. as time went on it would happen off and on and i simply ignored it. then one day it started and continued to do it. it now won't run below 2000 rpms(i'm guessing since i don't have a factory tach). i recently did alot of work to it replacing my leaking head gasket, also having the head and valve springs looks at by a shop to make sure everything was up to par. replaced all the top end gaskets. my intake/exhaust manifolds are tight with no leaks and new gasket. i've checked my vacuum lines and even found a vacuum diagram to make sure everything was in place as it should be. i still can't find what is causing it to idle high. my guess is it has to be something with the throttle body or a sensor. what's your opinion on my issue? Link to comment Share on other sites More sharing options...
cruiser54 Posted November 9, 2012 Share Posted November 9, 2012 There is a little gear driven Idle Control motor on the throttle body that can fail in the "stuck out" mode holding your linkage open a bit. Link to comment Share on other sites More sharing options...
Guest Posted November 9, 2012 Share Posted November 9, 2012 Sounds like the old ISC (Idle Speed Control) motor is on it's way out. Exact same symptoms I had before mine finally bit the big one. Link to comment Share on other sites More sharing options...
cruiser54 Posted November 9, 2012 Share Posted November 9, 2012 Sounds like the old ISC (Idle Speed Control) motor is on it's way out. Exact same symptoms I had before mine finally bit the big one. ISC. That's the name I couldn't remember with too little coffee flowing through my veins this morning. Link to comment Share on other sites More sharing options...
Brett486 Posted November 10, 2012 Share Posted November 10, 2012 could also be the tps (throttle position sensor), my 88 was idling super high, had it checked and came to find out that the tps lever was ABOVE the throttle control, where it should have been BELOW for accurate readings. pulled it out and put it in the right place and the idle dropped considerably. I had to tweak the idle up a bit cuz it dropped so much. Link to comment Share on other sites More sharing options...
airspeed Posted November 10, 2012 Share Posted November 10, 2012 If you trace the probelm to the idle speed control motor (ISC), that may be hard to find. The 83 Buick Lesabre 3.8 uses the same part and other GM's as well, sometimes it is called idle speed actuator (ISA). They actually sell a repair kit if you are up to putting the gear motor on the bench and taking it apart. Mount it in the vise and carefully remove the top. It is ingenious how they use the gears and sliding connetors to drive the fast idle plunger. Link to comment Share on other sites More sharing options...
ZJ_flexxxer Posted November 15, 2012 Author Share Posted November 15, 2012 Thanks guys, it has actually quit idling high on its own again but I'm still gonna look into these and make sure everything's how it should be. Link to comment Share on other sites More sharing options...
cruiser54 Posted November 15, 2012 Share Posted November 15, 2012 Be sure to remove the bolt holding the braided cable to the firewall. Scrape the firewall to bare metal and then reattach the cable. Link to comment Share on other sites More sharing options...
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