High Idle

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

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

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

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

First, stop on a slight incline, shift to neutral, release the brake pedal and see if the van creeps downhill on its own. If it doesn't suspect dragging front brake calipers.

Be sure the transmission is shifting into overdrive. I met one woman who said she was told to press the overdrive button each time she drove the van. That made it never shift into overdrive. Once she was set straight her fuel mileage went way up.

Tight universal joints will rob a lot of power from the engine.

Don't overlook spark plugs and wires. When one cylinder misfires, there will be unburned fuel and oxygen in the exhaust. The O2 sensor only detects unburned oxygen. That tells the Engine Computer to add fuel to bring the mixture back to normal, but it adds fuel to all cylinders. No matter how much fuel is added, the O2 sensor still sees that unburned air.

A similar problem can occur due to an exhaust leak ahead of the catalytic converter. Between the pulses of exhaust gas the momentum creates pulses of vacuum. That vacuum can draw in air. Again, the O2 sensor tells the computer to add more fuel to fix the perceived lean condition.

If you have access to a scanner you can read the fuel trim numbers. If they are very high positive, that means the computer is requesting more fuel in response to something. If the numbers are real high negative it means too much fuel is entering the engine and the computer is trying to fix that. The computer can only modify fuel mixture by plus or minus about 10 percent.

Caradiodoc