Quick question about the IAC. I purchased a new one off ebay and I can't for the life of me get the car to idle correctly with it. I have disconnected the battery, been through several driving cycles, did the IAC reset procedure several times and still wont idle below 1500, usually stays around 2000. No vacuum leaks. I put the old IAC back in and it idles as it should. (@800 according to my scanner). Is there a preferred brand for these things that works better than others (similar to how they dont like bosch o2 sensors). The old IAC, even though it will bring the idle down, has a hard time maintaining a steady idle. (jumps a couple hundred here and there). Just wondering if I should try a different brand. Rock auto has them in a range of $36 to $115.....do you really get what you paid for with these things? (I got a cheap one off ebay). 1994 Z28, 5.7L.

 

Yes, quality is what you pay, AC/Delco, Standard Products are two good brands.
Might be a leaky EGR valve.

 

EGR is brand new (valve and solenoid) but it has also been disabled through a tune.

 

did you reset the base idle,,, does it look like the idle set screw on the tb has been messed with?

 

I did the key on gas pedal thing according to shoebox. I have personally messed with the idle stop screw. With the new IAC, I had the screw all the way in. With the old IAC, I have to bring it out a bit to keep it running. When it's cold, with the old IAC, it idles around 500-600 and fluctuates up and down, acts like it wants to die unless I give it some gas. When it warms up the idle settles down to @800-900. The new IAC would never go below 1500-1600 RPM. The scanner shows the called for RPM's to be 800 in closed loop. Not sure what it is supposed to be. Seems even 800 is high to me.

 

base idle is 4 to 500 rpms. with a new iac, pull the valve/plunger out, install the iac, do not connect, the idea is to have the iac closed. start motor and set idle to 400. the iac if working correct is not closed all the way except on deceleration so unpluggin keeps it closed. once idle is set turn engine off and connect the iac and start. it will take a few runs to adjust.

 

I lost me a little on this one......

base idle is 4 to 500 rpms. with a new iac, pull the valve/plunger out, pull the plunger completely out of the IAC or out as far as it will go? install the iac, do not connect, the idea is to have the iac closed. start motor and set idle to 400. set to 400 with the idle stop screw? the iac if working correct is not closed all the way except on deceleration so unpluggin keeps it closed. once idle is set turn engine off and connect the iac and start. it will take a few runs to adjust. meaning a few times doing this procedure or drive cycles?

 

pull it out far enough so that its closed when installed. yes use the idle adjustment on the throttle body. and yes drive it normal. if the iac is working correctly it will adjust itself. the pcm/ecu will learn.