Engine misses, throttle up n' down!

Hi, I got a Dodge Colt AWD (Mitsubishi Vista) 2.4L 16 valves. There's something strange under the hood! When the engine reache 1500 RPM it start to miss so the RPM go down to about 600 RPM and than go back to 1500, and again, and again... it never stop. This happen in the 1500 to 2400 RPM range. Below or higher of that range, every thing is OK! No trouble codes are recorded on the OBD. Another thing is that happen only when the throttle in kept in still position, in car acceleration or compression it doesn't appears but when I keep the pedal in first or second gear at the 1500 to 2400 RPM the car is ridding like bull in a rodeo, not very funny! Please if anybody got an idea, it will be really appreciated.
Thanks

Tranny is my best guess

could be ignition. how's the ecu?

is this going on in all gears?

It doesn't appen only when engaged in gears, it's doing the same thing on neutral.
What I don't understand is why is it doing this unly between 1500 and 2400 RPM?
If it was a distributor problem it would do this at all time. Anyway the distributor has been changed and the trouble still there.
Any other guess?
Thanks

Still nobody got an idea what it could be?

Not sure if this mitsu engine is equiped with it, but check for an Idle Speed Control Motor. I had this problem with my Talon where it wouldn't hold an idle properly and rev up and then drop down, and up and down. It couldn't find it's idle points because the ISC motor was shot, so it just kept cycling.

Long shot, but it could be a throttle position sensor as well.

throttle body position sensor,map sensor,injectors,distrubutor

who ever said tranny is a moron

^ not as likely the injectors, more so the throttle position sensor, map or O2 sensor. Most likely the cause is the map (or MAF equipped?) sensor giving faulty readings to the ECU. It can be the sensor malfunctioning or a possible vacuum leak. Before replacing anything, check your vacuum lines and get a voltemeter to test the sensors for functuality. A crappy hanes manual will give you the correct voltages from the TPS, O2, and MAP/MAF at rpm specific intervals. What year is your car btw?

O2 sensors cannot be read properly with a voltmeter as the voltage produced should be constantly sweeping between appx. 0.10v and 0.90v. The changes also happen too fast for the voltmeter numbers to mean anything. A faulty o2 sensor will not cause the problems described. A throttle postion sensor will read about 0.80v at closed throttle and appx 4.80v at wide open throttle. The exact spec changes from car to car though and should be known before condeming any part. Like Moe Man said, the problem could easily be a MAP or MAF (if equipped) as well. Good Hunting :thumbsup:

It is a 1993 Dodge Colt Wagon AWD. This is one of the multiple names for the Mitsubishi Vista. OBD 1, Multi point fuel injection, not a throttle body. Haynes does'nt make repair manual for this car. Chilton neither. The only manual shop available I found for this car is the big bible used in the car dealers for $90, and I have to wait 3-4 weeks to get it by mail! Uncredible! When you ask for this kind of book, usualy it's because you need it now I guess.
The only thing I found on the internet is the trouble codes listing.
I checked it using a voltmeter between the No.1 and 12 terminals but there is no codes, only the regular short pulses non stop meaning that everything is OK! I bought this car from a guy at work recently and he told me that the car is doing this since many years, but he lived with it... he tought it was the clutch! If this my friends is not a moron... Anyway, he went to see the dealer with the car, they maid a diagnostic on it and everything was supposed to be ok. The problem is that the scanner can only reveal the stored trouble codes I guess, but cannot diagnose the engine while running.
I don't want to replace parts for nothing folks, I'm sure you understand my point.
Anyway talk to your friends about my problem, maybe somewhen, somewhere somebody will have an answer.

Thankyou everybody.

Engines can be diagnosed while running. It's called using an electronic engine analyzer. (Labscope).You don't have to have a DTC to be able to diagnose a problem. Most shops have one. Find one that does where you live and have them diagnose your car. It shouldn't be hard.