This is my first post so please be patient with me. I have had an erratic stuttering problem that used to show up only after engine was fully warmed up. Under hard acceleration it would occasionally miss and would surge at low rpm. This is on 305 with 5 speed tranny. Only mod is prom chip, which is only slightly modified. I have replaced oxygen sensor, mat sensor, plugs (not platinum), wires, cap and rotor, fuel filter, fuel pump, tested tps and it's in spec. Most recently I replaced the ecm which cleared up most of the problem except the erratic idling and low rpm surging. The engine runs fantastic at highway speeds and higher rpm now. I'm also getting excellent fuel economy now as well.With very little left to replace I am thinking the IAC motor (valve) may be the idling and low rpm problem. How can I tell if this part is working properly?

 

IAC sould not make a erratic stuttering problem because it will only let air in and make ur idle higher and not lower if the erratic studdering is from gonig in to low of a rpm it is not ur iac. kinda sounds like u have ur idle too low. have u checked it the correct way by putting the paper clip to make the iac close all the way up and then unpluge it then set min air? if not that is one of the first things u have to do to get a correct idle.

 

I did do the paperclip thing. But when I disconnect the IAC after resetting it, the engine races at 2500 rpm and I can't turn the idle any lower with the torx screw. Put the connector back on and it idles at around 600 - 650. If not IAC then what might this be?

 

Ok then that means your more than likely not letting the iac close all the way and your unplugging it when it is all the way open because if the iac was shut your idle will be at its lowest and if it is higher the iac is open letting air in kind of making it like a vacuum leak. I forgot what ports it is on the aldl thing but you have to use some kind of jumper (wire) and connect on to another and wait 15 sec and then pop your hood and unplug your iac and take the paper clip off. Then you take a flashlight or something and look down the iac port and see if the pin is all the way in and has closed the port. If so start your car and then adjust the idle (make sure the paper clip is out before u start it)