I know on the older GM vehicles, that screw was used only to set base idle. So, around 500 RPM or so, on a fully warmed motor, and IAC took care of the rest. I can't find anything in the service manual that even hints at that kind of procedure for the dodge motors..... everything says the screw is set at the factory, and not to touch it......

 

The procedure I listed is for a modified throttle body, which I thought I had read was being used. If it's still a stock throttle body with a plug over the idle screw, then leave it alone unless your tuner tells you otherwise.

 

I generally take what the FSM has to say with a grain of salt..... or two..... He isn't even remotely stock, so, all those rules go out the window.

 

So What I am trying to do is get the throttle blades set correctly. The throttle blade opening affects IAC counts. I have been playing with it the last 2 days. I think I have it however I am sure that my desired Idle needs to be raised in the PCM. On my scanner my desired idle is 744 RPM. Also I have a lopey cam 110LSA so Idle fluctuates 100+ RPM easy. Where I have my throttle blades set right now is giving me 35 IAC counts with the truck in park at idle. Drivability is good, no idle hang and no surging. Only issue is when i let off the throttle while driving and come to a slow coast, the IAC counts go to zero which drops the idle down anywhere from 475-575 until I almost stop or stop and then they pick back up. Obviously if I hit the gas and resume they pick back up as well. I am thinking that if the Idle was raised to say 850 or so it wouldn't drop down so far when the IAC cuts out because the throttle blades would be open a bit more. Does this make sense?

 

May make the problem worse too..... I think the best answer is to raise target idle in the programming, and then adjust throttle blades so IAC counts are somewhere in the ballpark. Otherwise, you will be using throttle opening to adjust idle, and that will bring on problems all its own.

 

In the post I mentioned raising the idle in the PCM. I have to talk to ryan and see what he thinks and maybe he can reprogram it. . Im kind of at a halt with him right now due to my spark knock issue. He feels something may have been assembled out of time being that we pulled like 10 degrees of timing from his table and Im still getting knock at 2000 rpm. So I still have to open up the front and check where the cam was installed and also want to check the distributer gear and make sure that is where it belongs at TDC. Im just messing with this right now until I tear it down this week. Ryan is a great guy to work with has the patience of a saint.

 

Distributor doesn't have anything to do with ignition timing. You can turn several degrees in either direction, and ignition timing won't change, Injector timing will though..... Have you set fuel sync? I would guess if the injectors were firing to early, or too late, it *might* cause some of your issues.

 

Yeah its pretty weird. Its only at approx 1900-2100 rpm under no load. I was spinning the tires on snow and it was doing it. I know the distributor only deals with the sync but as u said the injector timing may be off. I was told when I picked up the truck from getting tuned by PIE that they had to reset the dizzy cause the truck wouldn't start. They installed it in the first place but being that I am having issues, Im skeptical. I checked the fuel sync on the scanner its at +2.

 

+2 for fuel sync is within the range that the PCM can handle (+-9 IIRC). In any case all timing (ignition and fuel injection) is derived from the crank position sensor and the fuel sync signal determines the injector sequence for each revolution of the crankshaft.

 

This was the purpose of the procedure I had posted earlier. If you're IAC counts go to zero and idle is around 500, then you need to turn your idle up. I can't remember where exactly it is, but in the MT2500 you're using is a spot to test the IAC at different stages. When I set my idle, I used that setting and put my count to zero (closed) for a base idle test. Then I set the butterfly's to make the engine run at the target idle (750). My motor is a smooth running 408, so it behaves a little different than yours, but it should be about the same procedure.

If you want a fun experiment, make sure the IAC is closed and sealed, then unplug it and go for a drive. Mine was surging terribly trying to troubleshoot the same idle issue you're having. After that test drive and setting the idle to the target in the scanner, everything else fell into place. Now the only time the IAC is active is when the ac compressor kicks in, during warm-up, or when I'm idling around in the hills and lug it too far down.
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