I just got my motor back together. Lingenfelter 74211 cam with springs, port job, removed all the polution stuff, 52MM throttle body, Accell intake with large tube runners. I can't get my idle below 1500 rpms. I tried resetting the IAC. TPS is ok and correct. Car is a 91 L98 motor. There is no vacumn leaks. with it running there is alot of air being sucked thru the IAC port on the front of the throttle body. I removed the IAC and checked the length and it is OK. With it removed I went thru the steps to see if the pintal would move in or out, but it didn't move at all. I can feel a small vibration in it like the motor is running, but its not moving.

Does it sound like the IAC is bad?
It worked fine before I removed the motor, any ideas?


[Modified by cshuman, 2:41 PM 10/19/2003]

 

You could try a jump wire between A and B on the ALDL connector then turn on the ign.(don't start it). Waite a minute then unplug IAC connector. Then start your car. This should have extended the pintle and closed the valve. If it still idles high remove IAC and see if it did extend the pintle. :cheers:

 

I did that with it in place on the throttle body as well as removed. When I had it removed I measured the pintal length, then connect A and B on the ALDL plug to see it the pintal would move, it didn't, but I can feel a vibration from the motor in the IAC. It may be bad, but I find that hard to believe since it worked fine before I pulled the engine.

 

Anymore advice?

 

ttt

 

Sounds like the throttle blades on your TB are open too wide.

After jumpering the A&B connectors, turning the ignition to "on", waiting a minute and then disconnecting the IAC plug, start the engine and first try set ting the minimum airflow on the TB to an RPM about 100 RPMs below the desired idle speed that's burned into your PRM..

If your PROM is burned for 800 RPMS, closed-loop/idle, set the minimum air flow to 700. You can play with this number a little; you can try 650 or 750; see which works best for your setup.

Then shut down the engine, reconnect the IAC and fire her up and go for a drive of speeds around 40 MPH or so.

If you have Diacom or a ScanTool, your IAC counts should be around 20; but after doing a lot of fooling with mine, I found that my BBK 52mm TB liked 70 best.

My TB called for a more closed blade position causing a higher IAC count to maintain the 800 RPM idle speed burned into my PROM. Otherwise, my engine RPMs wouldn't drop when I let off the gas pedal. Had to play with it a while to get the setting right.

Your IAC counts should increase when the car is placed in gear and when the A/C is activated. As you rev the engine, the counts should rise and fall also.

If you don't see this count movement, your IAC is not functioning properly. Could be the IAC itself or wire(s), connection, maybe even the ECM.

Hope this helps.

Jake



[Modified by JAKE, 8:14 AM 10/20/2003]

 

It turned out to be a bad IAC valve. Ironic that it happened after I got the car back together. Installed the new one today, set the base idle, and it runs and sound great. Ordered a new chip from Ed Wright. New chip and about 500 more miles and I'll be ready to see how much difference these mods make.
Thanks for the input!
:cheers: