For about two weeks while idling in park or in gear but stopped in the drive-thru, the engine revs upwards of 1200-2100 rpm. Runs fine normally, no check engine light, no misfire and doesn't matter if the A/C is on or not.

 

What year is your Explorer? You might start by inspecting the throttle plate to make sure it isn't caked with carbon that is preventing it from fully closing. Be sure to open the plate and inspect the backside. If your Explorer has an electronic throttle plate you may opt to remove the throttle body to inspect/clean the back side.

Other things to check would be to inspect for a vacuum leak (which may not have other symptoms if the engine never gets below 1200 RPMs) and make sure the MAF, IAT, and ECT sensors are reading accurately. This is most easily done using a scan tool with datastream mode, then further troubleshooting any parts that seem questionable.

-Rod

 

It's a 2003 Mountaineer with a mechanical throttle not drive by wire. If it was a mass sensor wouldn't that show up on the Information Display and possibly bring up a Check Engine Light? It doesn't do this on a daily basis, but it's been happening for two weeks.

I don't know of any part stores that have a scan tool that can run a test, most are just the basic code readers. I'd personally rather not have to have my girlfriend go to a shop and pay to have it scanned, mostly cause I know a few people and they are silver tongued devil's if you catch my drift, plus they also just have a bad rep for misdiagnosing vehicles.

 

Depending on the cause, a bad reading from a MAF wouldn't necessary trigger a diagnostic code/CEL and certainly wouldn't cause any sort of statement from the info display. If the MAF is just reporting a unrealistic flow though based on vehicle speed, the PCM won't necessarily recognize that as a problem but rather just change air/fuel ratio and engine speed, etc. accordingly. Similar for an out-of-spec temperature sensor (intake air or engine coolant).

The place I'd start though is with the throttle plate and the idle air control passages. Also you might try unplugging the IAC to see if that causes a change in idle speed. If not, the IAC might not be working properly, or the throttle plate is open so much than the IAC has no effect. You could also try unplugging the MAF. If the engine stalls, it's probably doing its job.

-Rod

 

I'll see what I can do this weekend. Seems odd that it does it randomly rather than doing it more often or close to constantly. The other odd ball part is, if the MAF is going bad, then engine should bog down or lack power, at least from what I've been reading.

 

Oh, I didn't understand that it was doing this randomly. I understood your post to say it's been doing this for the past 2 weeks.

Since it's random, but repeatable, it really would be helpful if you could do some datalogging. If you have a smart phone, you might consider purchasing a OBD-II bluetooth dongle (cost anywhere from $10 to $300 and the cheap ones generally work just fine) and installing an app like Torque Lite (for Android) which would enable you to log multiple sensor data to compare between when running fine and idling high.

-Rod