Mechanics

HIGH IDLE

1989 Dodge Van • V8 2WD Automatic • 73,000 miles

I have a 1989 Dodge ram 250 van that I bought two weeks ago with a bad power steering pump. (Not the problem.) I went to pick up the pump and when I re-started the van it had an extremely high idle. I pulled the engine cover off and noticed that the sellenoid (sp?) Makes a kind of buzzing noise when the ignition is turned on and goes up but does not go down as the engine warms up, thus making the idle higher and higher. I don't have a manual for her yet, and would greatly appreciate any feed-back on this problem before I tear into it, I'm thinking either a bad sellenoid or perhaps a temperature sensor. Thanks!
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Azmodeus
January 29, 2011.




Can you describe where that solenoid is located? And you do have throttle body injection with two injectors right? Or does it have a carburetor yet? Does that solenoid have two or four wires? Do you have access to a scanner?

Caradiodoc

Caradiodoc
Jan 29, 2011.
Solenoid is located at the linkage next to the throttle body fuel injection on top of the engine. Two injectors with four wires running to the solenoid. No access to a scanner without visiting a shop. I know there is a method for getting codes without a scanner but I haven't done that yet as the problem just developed. Thanks again!

Tiny
Azmodeus
Jan 29, 2011.
The more I think about it, it may not be a solenoid but an IAC?

Tiny
Azmodeus
Jan 29, 2011.
Yup, with four wires, that's the automatic idle speed motor. It should buzz when you turn the engine off or when you turn the ignition switch on. It is turning to retract a pintle valve on a threaded rod in preparation for engine starting. By retracting, it opens up the air passage around the throttle blade. That, along with an increased injector pulse width, raises engine speed to produce the idle flare-up to 1500 rpm when you start the engine. It should come back down to 800 rpm within a few seconds.

There's two plans of attack. One is to spray water around the intake manifold gaskets, base of the throttle body, throttle shaft bushings, and vacuum hoses when the engine is still cold to see if you can find a vacuum leak. The second thing you can do requires a scanner to view live sensor data. In particular, you're interested in "AIS steps". The automatic idle speed motor can turn a total of about ten revolutions and as it does, a threaded rod retracts that pintle valve. Within those ten revolutions there are 256 imaginary "steps" or positions the motor can stop at. The higher the step number, the more the valve is open. What you should expect to see is it's close to step 32 when everything is working properly. If you find it much higher, say around step 50, the Engine Computer is requesting the higher engine speed in response to something. Typically you will find it around step 0 to step 5 meaning the computer sees the engine speed is too high and is trying to bring it down. That's what happens when there is a vacuum leak.

Caradiodoc

Caradiodoc
Jan 29, 2011.
Thanks, that clears it up a little but is there any other way to diagnose it without a scanner?

Tiny
Azmodeus
Jan 30, 2011.
Oops, forgot to add that it does not seem to be a vacuum leak.

Tiny
Azmodeus
Jan 30, 2011.
You can remove the AIS motor, leave it plugged in, then see if the valve moves in and out when you turn on the ignition switch. If it doesn't move, you can try pulling the valve out to extend it. (It pulls out hard). Reinstall it that way, and idle speed should be lower.

If the valve never moves on its own, the assembly may be defective.

Caradiodoc

Caradiodoc
Jan 30, 2011.
Thought of that, However I want the system to function correctly so it looks like I need a scanner. Thanks for all your help, I'll let you know what the ultimate solution is. -Azmo

Tiny
Azmodeus
Jan 30, 2011.
Yup. I didn't mean to imply that was a way to cobble it even though that's what I appeared to type. Rather, what I should have stated is that's a way to verify if the valve is moving or not. It would be real nice if it was not moving which means a new AIS motor might solve the problem.

Will wait to hear back.

Caradiodoc

Caradiodoc
Jan 31, 2011.
Well, as it turns out it was the IAC. The motor itself was functioning but the adjustment/actuator was stripped on the inside making it ineffective. When testing, it seemed to function properly but if you put any load on it, it would fail, producing no codes from the computer, it took me some time to figure this out.
On a different note any ideas on how to increase my MPG fromm that 5.2 Litre 318? The original MPG is 11 city and 13 highway, I got 8.76 MPG on the last fill-up, granted I've been working on her and tuning her but WOW that's miserable. Any ideas would be very welcome, thanks again!
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Tiny
Azmodeus
Feb 14, 2011.

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