In recent months my car's idle has been too high, sometimes going up to 1600 after start before gradually coming down over several minutes to about 1200 in park and about 950 in drive. I replaced the EGR valve and the solenoid (had an EGR check engine light on -- it went off after that). At the same time, I replaced the IAC, but the new IAC seemed to make it worse. I put back the old IAC and did a full retrain (battery off for a half hour, then on; key on for 20 secs; key off; start car and wait for warmup to full temp; turn off; turn on, then off; start and idle for 3 minutes; brake and put car in drive for 3 minutes; put car in park and shut off for 20 secs, then start).

During the retrain on warmup idle, the RPM went from 1500 down, then back up, then down farther, repeating until the low was about 700 but then it gradually trained back up to 1200 in park and stayed there. It is now between 850 and 950 when in drive with brake on.

I understand that a high idle could come from many causes, but I am confused that during the retain the idle dropped slowly all the way down to 700 but didn't stay there. It went back up to 1200. When the car was younger, a battery off made the car retrain with low idle, not high, and I had to keep the AC on to avoid a stall until the retrain finished in a few hours of driving. I would really like to get the idle down to 700, because otherwise it strains the transmission during idle and during initial shift into gear. I am wondering if it could be the throttle position sensor.

The symptoms now are: a) on start the revs shoot up to about 1800 and then fall slowly over a few seconds to about 1200, at which point it's low enough that I can shift into gear without damaging the transmission, but there is still a big clunking sound when I do. b) the idle in park when warm is still 1200, and the idle when in gear with the brake on is about 850 - 900. I would like to get the curb idle to around 700. In years past it did idle there, so something must be wrong.

My oxygen sensors show variation between 0.08 and 0.65 (approx) volts on the graph. I have a Zenith scan tool with live data. It is my understanding that my base idle must be set with a special Mitsubishi scan tool to program the ECM (assuming that's the issue). I also saw that one can jumper two DLC pins in some models and then adjust the airflow screw on the throttle body, but I don't know if that works on this model.

I can just take it to a dealer and throw money at it, but I recently had some major expenses on it already, including a timing belt replacement, and am hoping to avoid additional large $, since this car is nearing the end of its useful life. Any suggestions would be greatly appreciated.

 

Check your throttle position sensor idle position in your scan tool, It should read 0% when no throttle is applied. Next thing I would suggest is to look for vacuum leaks. Another thing to consider is the sensor plugged into the side of the power steering pump, it bumps the idle up when steering at idle so it's easier to turn the wheels, if the wire is frayed or corroded there is a slight chance it would cause this behavior but it's extremely uncommon. A dirty throttle body could also cause this, purchase a TB gasket, pull that sucker off, take it apart, and thoroughly clean everything.

 

Rather odd symptoms. Drove car about 3 miles to Advance Auto to buy the throttle body cleaner spray. During the trip the idle dropped to 700 at stop lights, and I thought it had trained to a fix. Bought the spray anyway. When I restarted the car, the idle went back up to 1200 in park and about 900 in drive, but varied at each stoplight, usually down to about 850 in drive. Here are scan tool measurements at idle in park.
Fuel Sys 1 CL
Fuel Sys 2 N/A
Calc Load 19.2%
ECT 95 deg F
STFTB1 about 5%
LTFTB1 0.0%
Eng RPM 1223
Veh Speed 0
Spark Adv 22 deg
IAT 102 deg F
MAF 0.77 lbs/min
TPS 1.2%
OS2B1S1 varying about 0.12 - 0.42
STFTB1S1 5%
OS2B1S2 varying about 0.08 - 0.6
STFTB!S2 5%

If the TPS is not 0 on idle, is it low enough for a base idle or does it imply that the throttle butterfly is not closing completely or that the TPS may be bad? What puzzles me is that, after I have driven a while, the idle drops down to spec at stop lights, but if I stop the car and restart it, the idle goes higher. Whenever I start the car, the idle is about 1600 and then drops over a few seconds down to around 1200, or a little higher when the engine is cold.

Any further advice would be welcome.

 

 

What is that Spoiler button for?

 

It appears that the high idle was a result of a vacuum leak somewhere in the hose system, although I am not sure of this. The symptom improved after I had work done on my vacuum-powered 4 wheel drive at AAMCO (expensive) and the mechanic told me they had found and fixed a vacuum problem. I had already made some likely ill-advised adjustments to the throttle, so the ECM choke routine may be a little confused, but at present the car initially starts up with idle at about 1,200 and later drops to about 800 or less after warmup. I have seen other approaches to high idle on the web, such as putting in a perforated gasket to restrict max airflow in the control module, and was going to try that next, but right now my idle issue is under control enough that I'm going to leave it this way. My thermostat is also defective, running the engine too cold for a long time, but that problem is newer than the high idle.

I had a new timing belt put in to keep this truck alive a few more years, but the next time something major goes wrong I will probably have to scrap it.

 

leoj......Thanks for the detailed update. Ummmmmm.....vacuum leak......I will have to look around all those miles of vacuum hoses and see what I can find.
1200 rpm, then down to 800 is decent.....I could live with that too.
But I am like you, and hate to shift into gears with it revving around 12-1400rpm....just aint healthy for the old girl's joints, arthritis, and roomatism.
Scrap it????? Oh no......maybe someone will buy it and do a full resto to keep her rollin another 20 years.

I just started a thread about replacing the Head Gasket on my 94 Montero......put up some pics about the huge amount of oil I found in the "valley" of the engine. Will be popping off the valve covers and heads real soon and take a peek.