Unfortuantely that was one of the first things I replaced because it was cheap and easy. So far I've doen the IAC, TPS and CTS.

I should probably also mention that the van idles perfectly. Purrs like a kitten when idling, either in park or when in gear... it's only when I begin to accelerate that I have the problems, and not even all the time which makes it even more perplexing.

I don't know if this bit of info has any value but I thought I'd mention it. When I replaced the CTS I had to remove the alternator to get to it, thus the battery was disconnected for over an hour. Could that be the reason why once everything was done the van drove as I expected?

 

I realize you already replaced the IAC and wasn't suggesting it was bad, although new parts can be defective. I said it could be "an IAC valve control issue" meaning that something could be causing the IAC valve open and close when it shouldn't. By disconnecting the IAC, you can determine if it's operation is the cause of the noise and reving. Once you know that for sure, the problem is now narrowed down to what is causing it to operate/move/open.

 

Here's a little something I discovered that I think may be of use. I played golf all day yesterday and when I drove home that evening the van drove perfectly the entire time. As opposed to how it drove when I drove to the golf course that afternoon. The only difference was that in the evening it was cool outside instead of about 95 degrees. So it seems that whatever the problem is it's caused by a combo of the engine temp and the outside temp

 

I believe the only sensor effected by the outside air temp is the MAP sensor, mounted on the front of the throttle body.

 

My '89 TBI has a temp sensor on the throttle body called the air charge temp sensor. Idk if your year does.

 

On the Magnum's they are mounted in the Intake on the right side towards the front and called Intake Air Temp sensor.

I think Alloro is right about the MAP sensor. For it tells the PCM what the outside air density/pressure is just before start up and then what the intake is drawing as the engine runs. If it is clogged or leaking air then its readings would not be correct and would greatly affect the fuel ratio and shift points of the transmission.

 

Thanks everyone for your input. You've all really been great in helping me track this thing down. The IAT is fairly cheap so that's something I can just replace. As for the MAP sensor, those are a bit pricier. Any idea if that particular sensor can be tested?

 

First check the rubber L boot for damage, if so replace.
The Black/Lt Blue wire is ground
The Violet/White wire is 5 Volt Positive
The Dark Green/Red wire is the one that sends the signal back to the PCM.

A DVOM with wire piercing probes will help in the following test. Testing the voltage of the Dark Green/Red wire to the Black/Lt Blue wire should be 4-5 volts with the Key ON Engine OFF. And 1 to 2.1 with the engine running, at operating temp, and neutral idle speed condition. If you live at higher elevation than the readings might be slightly lower than the 1 to 2.1 voltage reading.

 

FYI, only multi-port fuel injected magnum engines have the IAT sensor, TBI ones do not.

 

On a side note, upon looking things over I discovered a leak that needs to be addressed... does anyone happen to know what this valve in the pic is called?