89 ram van b250, 318 engine.
All this happens whether the engine is hot or cold, driven long or short time.

IAC works OK to start engine.

After a few seconds the idle goes down to where it should be.
I drive a few blocks and when I get to a stop sign, the IAC has kicked the rpms WAY high, way more than high idle at start up. This also happens randomly, regardless of what type of driving I am doing. I dont notice it until I get to a reduced speed zone or a light or stop sign and then have to cram on the brakes to stop the van.

It never happens when at a stand still, only when I have the accel. pedal depressed. I know it's the ICS because I can feel it in the throttle pedal...it's partly depressed with no foot on it.

The rpms it goes to are not the same every time. sometimes it's like 30 mph and sometimes it's 50 mph.
Sometimes it happens 3 times in 30 minutes and sometimes it happens once a day....

Totally irratic...

temporary fixes while I am driving;

I put the van in neutral and rev the engine up and down, and half the time this eventually (within a 15 seconds) drops the IAC idles down to where it should be.

I put the van in neutral while I am driving and turn the engine off, then on again and most of the time this solves the problem. on and off reactivates the IAC to it's start position, and then goes to normal idle.

Solutions I have tried:
I replace the TPS (an expensive proposition at the dealer...then found out it was the same part for half the price at Pep Boys...)...did nothing to help

Removed the batter cable for 2 hours to reset the computer...did nothing.

A buddy of mine thinks I need to remove the throttle body and clean it I ( I think it's a shot in the dark....) but I don't see what that has to do with the IAC. As I understand it, it's controlled by the computer using the TPS and the temp. sensor.

Before I take the throttle body off, what else could it be? Is this a computer gone bad?

ANY help you can give would be GREATLY appreciated! My gas milage has gone down the drain and I'm sure it's not good for the brakes!

Jim

 

How about cleaning or replacing the IAC valve?

 

It's not a valve...it's a dumb gear driven solenoid...essentially a fancy pusher that pushes on the throttle arm. It's whatever is electrically telling it to push or not push that's the issue. There is no sensor inside, just a motor and some gears that push on a rod, 3 wires..one is common and the other 2 are forward and back.

I heard from another forum that I should rebuild the throttle body...I want to explore all other options before I go there.

 

The throttle body is easy enough to clean. There is a plate on the backside with several different vaccuum amplifier ports. The barbs are kinda fragile, use care. Mine was almost obscured with carbon, and after cleaning ran much much smoother.

But the only thing that might possible tangentially affect the ISC pintle is the Map sensor vaccuum line.

You should also check the wiring at the computer connectors. I found some previous "mechanic" stabbed many of the wires next to the connector with a probe and they corroded out from within and have caused me issues in the past and more recently too, and getting a new 14 way connector appears in the unobtanium column.

I have an '89 too.

Clean the ECM ground at the foot of the coil attachment on intake manifold too.

 

I replaced the IAC with another used one and problem is fixed. Easy repair and took only about 5 minutes. Have yet to open up the old one to see what the problem was but when I cleaned out the newer one to oil it, there is a switch inside that tells the computer when it's fully extended ( and maybe as a reset of distance) and I wonder it isn't working in the old one.
Didn't touch anything else, so it's got to be the answer. Never ran so good!
Thanks for all your help and suggestions.