I have an 87 305TPI with an automatic bone stock except for the wiring harness that was changed by the previous owner. It idles really high and has since the day i got it. I have checked all the connections and realays and they all check out good. all the sensors seem to be getting the correct volatge. i have tried to set the minimum idle by IAC and it desnt drop below 1500 even with the idle scew COMPLETELY out. the TPS is at .54 at idle and 4.5 at WOT. I have sprayed the intake with water to see if it changes the idle and it doesnt so there is no leak. i have also disconnected EVERY line individually to eliminate that possibility. Could it be my computer? I have checked all the voltage coming from the computer based on the wiring diagram and everything is good. Could the computer itself be fried? The check engine light stays on but it wont let me pull any codes when i jump it. I also tried to run winaldl and it wont give the computer any info. ANY HELP would be greatly appreciated.

the car has the 1227165 ECM in it if that helps.

John34683@yahoo.com

 

does ur car have a cooling sensor? Is it carb? If its a carb it could be a choke problem. If its f.i it may be the cooling sensor and or sender. they act as the choke for the f.i's. I assume by the age of your car she is carb but since I came here I gave up assuming lol. Let me know how it goes.

 

It is F.I. i checked the resistance on the coolant sensor and it is within spec. What should the voltage be on the two wires? one is black the other is yellow.

 

Bad IAC (idle Air Control valve)? It's underneath the TB and is what the ECM uses to control the idle speed- kind of like a little tiny throttle that opens and closes under ECM command.

 

How do i test the iac? I know i removed it and cleaned it up but i havent been able to find any specs on testing it.

 

I don't know, but they are a stepper-motor based on ECM input. I have caught them when I do the base idle setting. You know- start the engine, warm it up, hod revs over 2500 for 2 minutes and unplug the IAC while still revved up then let the throttle close (I don't recall if that's the exact procedure- I haven't done it in years now, but I recall it being something like that). When you let it back down to set the base idle speed at the TB screw it should idle way down becuase the IAC SHOULD be fully closed at this point, if you do the procedure correctly. If it's still holding a high idle and the screw is backed all the way out (and you're sure you have no vacuum leaks) there's a good chance the IAC is "frozen" and not moving (i.e it's toast) OR the wiring to it from the ECM is damaged.

But before you try any of that I'd wonder about your ECM. Not being able to spit out codes or hook up a diagnostic scanner to the ALDL is NOT a good sign that your ECM is working properly.