Help with the family hauler...

[fastivaca]

Here's a test for the vast automotive knowledge base we have here at ff.com!

I have a 2004 Pontiac Montana that's giving us some grief at the moment.

- intermittent very fast idle speeds (2000rpm +), becoming more regular. At times the van will hold 50mph without touching the gas pedal :nightmare:
- IAC valve replaced last week. Ran OK for a while then reverted back to the fast idle.
- just started to run hotter than usual too.
- no check engine light
- all fluid levels where they should be
- even when idle is where is should be there is what can be best described as a rumbling noise when stopped at a light.
- I can get the idle back down for a while by removing the battery fuse for a minute or two.
- currently has about 365,000km (227,000 miles) on it

I plan on taking it to a McParts store in the morning to throw a code reader on it.

Any suggestions or diagnoses would be greatly appreciated

Thanks

[crazyrog17]

High idle can be a vac leak problem

[lessersivad]

With no CEL lit up and the high idle, vacuum leak gets my vote also.

[fastivaca]

Thanks for the suggestions. Just took the van up to the local McParts store and had them plug in the code reader.... no codes found. Did the brake/carb cleaner vacuum leak test with no noticeable results. Sprayed around the main vacuum lines, the intake system and PCV valve to no avail.

Unplugged the main battery fuse for about a minute and the idle has returned to normal.

I'm going to nurse things along over the Christmas break and see about further diagnosis in the New Year.

[crazyrog17]

Must be electronics/sensor related.

[tooldude]

I can't say I have any special knowledge about a Montana, but I would sure be checking on that rumbling noise that may be a precursor to a breakdown or some serious damage. At least look at the serpentine belt and pulleys/fan for anything loose. If you have a stethoscope listen to the water pump bearing, and others, alternator, idler pulley, and around the torque converter on the trans. Have your wife hold the brake and shift from D TO R to check engine/trans mounts for movement that may make metal contact or pull on wires/hoses. Interrogate your wife, carefully of course, like "Sweetie, I know you're a good driver and all, but did something happen that WAS NOT YOUR FAULT OF COURSE like a big pothole in the road or a STUPID curb in the wrong place that you forgot about because you are so busy doing all you do for us?" Was there any previous problem or work done?-there's not enough to go on. Throttle could be sticking, air in system or ECT getting out of range causing engine to idle up for cooling, water pump impeller loose or worn not pumping well. I'm wondering if removing that fuse could possibly be causing the computer to go into a relearn procedure.

[DriverOne]

Check the catalytic converter.