Hello I have a 94 sc400 with no idle and if I give it any throttle or let air in the system it will start. I'm getting a constant ground to the iac on a pin, s4 I believe, anyway I have replaced the maf, tps, and ect with new OEM parts and new connectors. I also had my computer rebuilt almost 3 years ago when I started getting random codes before my cd009 swap. Has anyone ever encounter this problem my iac tests good and to me wouldn't matter if it's not getting grounding pulses to the other pins.

 

If I remember right the middle 2 pins (pin 2 and 5) have 12V power, and the other ones are pulsed to operate each stepper motor (there are 2) for each direction (2 for each).
Probably shouldn't have constant ground, If I had to guess I would say something in the ecu is doing it, maybe look to go standalone or a working ecu somewhere.
I don't usually opt for rebuilding but lots of people have done it, I have always been skeptical of going down that route.

temporarily you can try and move it to a middle position or disconnect the pin that has become a constant ground and its related pin, I think 1 and 3 go to same stepper, and 4 and 6 go to the second stepper, not sure what kind of idle control will happen without one of them and the stock ecu but maybe better than whats happening now.

 

I pulled the wire harness with the engine when I manual swapped it and removed the sheaths and wrapping to replace it and while I was at it I checked the wires and they all seemed ok I.E no burnt spots, cracking, pinches or the likes. I was hoping there was another sensor or system that would control idle but I'm thinking my ECU has died again while setting during the swap. Do you have any experience with a stand alone ecu?

 

Little update i guess my test light coudnt keep up with the ground pulses so I pulled the trigger on a new iac, my old one turned out to be junk the ohms shot up once it got hot and stopped moving with manually applied ground. Now my new problem is the iac only opens while cranking then once it fires it fully closes choking itself out. Does this still sound like the ECM to anyone?

 

I assume you have checked for air leaks?

 

I have, ive looked at all the diagrams, traced them down and replaced them when the motor was out and went back and made sure nothing was crossed or missed. I also sprayed some started fluid around the intake and vac lines to see if it would suck any up. I can get it to start and idle by making a vac leak at the power steering idle up on the intake, so I dont think it's a vac leak, but again its still not the right way it should idle. Would the egr delete i put on when I changed headers make it not idle its a 94 OB1 and from what I read it shouldn't have affected anything