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Runaway Astro--high idle problem

Jon Heddleston
02-28-2008, 10:02 PM
Help! My 2000 AWD Astro thinks she's a mustang. Without provocation, she jumps idle to what feels like 4000 rpm and will not kick out of that high idle mode. (The Astro has no tach--so this high idle sneaks up on me!) This is the 3rd AWD Astro I've owned, but none has harassed me so. Vacuum hoses have been replaced--a new "intake unit/sensor?" installed ($157 just for the part, remanufactured)--but high idle resurfaces without warning. Any one out there with LOTS of experience with this otherwise great 4.6 ltr workhorse motor? I'm online because the cost of chasing rainbows at the shop is killing me--and the high idle is wearing out the Astro's brakes and my desire to keep this pretty "Regency" conversion colt. Sorry, I don't know what codes have come up--but each has been neutralized one by one without solving the problem. What I do know is that I've spent $500+ with no healing for Astro or me. Please help before my brakes give out....Thanks. Jon Heddleston (Virginia)

02-29-2008, 05:27 PM
Autozone and Advance Auto will retrieve the DTC's at no charge... extremely helpful in diagnosing problems. Most likely cause would be the Idle Air Controller, (IAC). Located on the driver side of the throttle body. Might be the motor is sticking or dirt in the air passages. Best to get the DTC's and go from there rather than throw money at it needlessly.

02-29-2008, 09:38 PM
could be an air leak at plenum gasket- Mine did that-could see the greasy spot around the leak up front--sets code 35 high idle--I put a ballon up against it-and it slowed it down

03-02-2008, 07:29 AM
Look at the fast idle solenoid , it's in front of the throttle body and is about 2 inches round. It maybe faulty or has a piece of debris or carbon stuck in the orfice , it is driven electrically by the computer . I know of several people with a faulty solenoid and they never got a dtc code from it so we had to just replace it and hope for the best.

Blue Bowtie
03-02-2008, 09:24 AM
... My 2000 AWD Astro thinks she's a mustang.

Why is that? Is it rusting out at the spring towers? Is it unable to to drive straight because the body is twisting? Is it grossly underpowered and unreliable? Does it have an oil burning modular engine? Just checking...

Anyway, the item described above is the Idle Air Control, and it is a two-phase stepper motor, not a high idle solenoid.

The CPFI system on your engine uses a single throttle body. The throttle plate in the body can become contaminated with environmental dust, oil vapors, and fuel vapors. After time, these deposits will create a varnish which coats the edges of the throttle plate and its bore. The deposits can cause the plate to stick or bind in the bore, and not close fully. You will need to remove the air horn from the throttle body, open the throttle plate manually, and clean the varnish accumulation from both the plate and the bore. A spray type carburetor cleaner works well for this. An old toothbrush can also be useful in reaching the less accessible places in the bore. Try to avoid getting any cleaner onto the Throttle Position Sensor.

The rectangular air passage near the top of the TB should also be cleaned, since this is the source for the Idle Air Control (IAC) air. Once the TB is cleaned, operate it through the entire range manually several times to check for binding and sticking. Also check the throttle and cruise control cables and bellcrank for sticking and interference with other objects.

If you thoroughly clean the throttle body and the problem persists, you might suspect the IAC. The IAC can be removed, disassembled, cleaned, and relubricated to restore proper performance.

If the throttle body is clean, the IAC is cleaned and active, you can suspect other vacuum leaks, control problems such as an intermittent CTS or TPS signal, or electrical connections.

03-02-2008, 10:51 PM
If it turns out to be none of the above problems I was just thinking that short of a vacuum leak I wonder if the pcv valave could cause this high idle ? Just a sugestion anyways , let us know if you get it solved.

11-16-2014, 10:12 PM
My '02 Astro has developed a high idle problem. With winter setting in, I have to kick it into neutral every time I come up to a stop sign or it wants to keep going. I replaced the idle air stepping motor but it didn't help. It takes off at about 2000 RPM on cold startup and eventually drops to around 1000 RPM once it warms up. If I stop and put the tranny in PARK, it drops to a normal idle in a couple seconds. My Haines manual talks about a pressure switch on the power steering which increases the idle to compensate for load on the engine when steering is turned or brakes are applied. However, I can't find the switch. Because it eventually slows down, I don't think that it is a major air leak or blockage in idle air circuit. Anybody knows where the PS pressure switch is? Thanks!

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