idle problems with 91 laser 1.8

[Chaddsmcollecto]

i have major idle fluctuation in my 91 laser 1.8
first i thought IAC (so i changed control motor as well as the plunger)
Then i thought throddle position ( changed it)
so then i thought some vac leaks (currently changing vac lines) no luck yet
does anyone know what would cause idle to go from 500 rpm to 2200rpm by itself
this happens anytime i let off the gas up down up down
and when i m traveling at low rpm constently it will hesitate then take off hard enough to spin the tires
also once in a while it will skip or miss and not go above 1500rpm until i shut the car off and restart it then it runs fine

however above 2500 rpm it runs fine with no difficulties

although it is fun to fly everywhere to ensure the rpms stay up it is getting a little annoying when driving through heavy traffic

i have been working on DSM for a long time and i have never came across anything like this before

considering this is my winter beater im sure when the snow and ice comes this could be a bit interesting if i can find the problem by then

please someone give me some ideas on what else it could be

 

[1.8laser90]

have u tried reseting the ecu ? are any check engine lights on ? if reseting the ecu doesn't help warm the car up and disconect the isc motor and see if the idle pounces if it still does it nothing in that area... after doin this let me know

 

[Chaddsmcollecto]

i tried disconnecting the IAC when it was warm and still have the problem
i also reset the ecu still same thing it is really the wierdest thing i ever encountered

 

[adgrey]

FWIW, I had the same problem with my 91 Laser 2.0 and it turned out to be the Idle Speed Control Servo. Molded plastic piece with two coils, two windings per coil. It was easy to test for. Just pull off the connector and check with an ohmmeter. One of the windings was open. A Plymouth dealer wanted $395 for it, there's a web site offering rebuilt ones for $100. Found someone here who sold me one with a bad coil for $10. Soldered/desoldered and combined the two good coils into one good unit. BTW, care to give me an opinion on my Power Loss post?

Andy

 

[1.8laser90]

pretty clean 1.8 u got!... check the the maf sensor they can be really screw i have had one go bad and would only do it when ever it wanted if its ok id swap ecu's or check and see yours is ok (like caps and that they havn't leaked on the board) thats all i can think of right now.. o and another thing that might be it the reed switch that can mes with the idle. search on the www.dsmtalk.com on the 1.8 forum about it... this must be a mystery..