2008 Mitsubishi Lancer: Rev Hang

Try the low tech fix...make sure the floormat isn't bunched up under the pedals.

Car is probably angry at you. I guess this and the Enclave got together to be modern day Christines.

I'm guessing either the floormat, or a bad mass airflow sensor. Did the check engine light come on?

My 1991 Eagle 2000GTX AWD (aka Mitsu Galant GSX) with the 2.0 DOHC engine did this same thing! This erratic high idle happened just as you described, from the time the car was 4 yrs old (Sept 1995 with 57,000 km)'til I sold it in Jan 2000 with 170,000 kms. No garage, including the dealer, could ever diagnose the problem. Since it had a manual trans, I was able to live with the problem. It only happened below 40 km/h (25 mph) and never above that speed.

It wasn't the floormat because the revs returned to normal while I was just sitting there at the stoplight, not fidgeting with anything and just watching the tach. And the check engine light didn't come on. In fact this problem didn't pop up again for the rest of the weekend I had the car.

maybe a cruise-control glich.

you have a electric glitch or something is going out- throttle position sensor, ignition control, or a leak in the vacum system/egr, etc all need to be checked out.
 
it could be that combination of events just made the ecu 'glitch' for a moment, never to return... but makes me think something is faulty or on it's way out.
 
fwiw, I had the exact same thing happen on a Audi A4 manual transmission- vacum leak

This sometimes happens in my Focus too. After cruising down the interstate and pushing the clutch in to coast down an off-ramp, the revs will stay relatively high (2-3000 rpm) until I come to a complete stop. If I coast for 60 seconds, revs stay up for 60 seconds. Not a big enough nuisance to have someone look at it -- I suspect it's for emissions reasons like vacagrande said. Sounds like it's a little different from what you're saying though: that it was revving high even after you stopped. Seems like a big waste of gas... 4500 rpm under no load would use 6x as much fuel as 750 rpm under no load (idle). If it's a problem (ie not built into the car's design) then I imagine there's a software fix for it.

greenpony,
there is no reason for the revs to stay up. If it were an emmissions feature, it would want to minimize exhaust. (i.e. - cut your engine any time possible, not rev it)
 
The typical problem is a cracked, loose hose in the vacum or throttle mis-adjustment. It's typical as vacum leaks are common and symptoms don't readily appear.

"not going in for it's periodic maintenance...." i guess these long-term tests are more realistic than i thought!

It was payback for making it go by its friends on a donut.

I assume it's an electronic throttle? Has the clutch felt squishy or jangly? It could be a pneudraulic problem. Check the fluids and make sure your clutch isn't engaging mistakenly.

This just in.....Problem Identified - it's a Mitsubishi!

This just in...Mitsubishi's happen to be very reliable. I don't own one myself, but my brother owns a 1999 Galant and another relative has an 2001 Eclipse. Both have over 100,000 miles and they have only had to get new tires and oil!

My 2008 Civic Si does not have a Rev Hang problem at all. So Honda did fix that problem.

my 2002 lancer has a similar problem.Rpm will run 3000 at start up, and at times 500. Other times rpm will go from 1000 to 2500 by itself driving. Thats not good
I looked on the net and found throtttle position sensor recall. I'm still searching

Actually I am betting on a sensor. That's right, an $18 sensor. We were the recipients of a 99 Caravan in excellent condition despite 100k miles. We were on the highway and the speedometer started bouncing between maximum and minimum. Anyone who has ever driven a minivan knows that the don't do well at 100+ MPH. And slowing down at a tollbooth only confirmed it. The speedometer stopped working at all and the engine was suddenly running very high rpm and would not shift. Turns out there is a sensor on the output shaft of the transmission that is magnetic. Got a code for the sensor and car was stuck in 2nd. Replaced $18 sensor, speedometer works perfectly, transmission shifts perfectly. Bet on the sensor;) BTW, we love the van. Works like a champ.