Mitsubishi Repair: 1990 van throttle pulsing, accelerator pedal, exaust

Question
Hi!,

Thanks for the reply. I have no way to tell if the computer is the right year for my engine because I don't know the year of the engine.  It was replaced.  Are there some date codes on it somewhere?  I've owned the van for about 2 years now and I haven't had this problem until a couple weeks ago so I'm wondering why the computer would act up all of a sudden after this long a time of running fine.  If we eliminated the computer thing what else do you think could be going on?  
Thanks alot,
John
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The text above is a follow-up to ...

-----Question-----
Hi,

I hope you can help me out.  I have a 1990 Mitsubishi van, 2.4 engine, automatic.  Recently when starting it up in the morning after not having been driven since the day before, it will drive normally for about 5-10 minutes then all of a sudden the engine begins an up and down throttling between idle speed and 2000 RPMs.  It will idle normally during this situation but as soon as you push the accelerator pedal down approaching 2000 RPM the throttle pulses up and down between idle speed and 2000 RPM.  It continues if you keep the pedal where it is or more.  It does this routine for about 10-15 minutes allowing me to only do about 10MPH, which is such a joy in heavy traffic!.  I get alot of fingers from people behind me if you know what I mean.  After the 10-15 minutes it goes back to normal magically and doesn't do it again for the rest of the day.  This happens every morning now for the past several weeks.  I noticed during the pulsing that the exaust smells kinda funny and sometimes there is a minor backfire.  I can't get it to malfunction long enough to get it to a mechanic so they can see what it's doing.  By the way, the engine has been replaced in this van so it may or may not be a 1990 engine - it must be real close though.  My ECU was just rebuilt and doublechecked as working fine.  Hope you can help.

Thanks!
-----Answer-----
John: Are you sure that the ECU goes with that engine? Could be the ECU is programed for a different engine, so it is trying to run it's program but it is the wrong program for the engine in the van. I have read that you are to make sure you use the right ECU and it has to be with the right engine other wise the two do not run right together. Maybe after a while all the sensors bring their thoughts to the EUC and it gets it's program changed and so the van runs ok. But then come morning the ECU has gone back to it's planned program and so it all happens again. So you need to check on that engine to see it and the ECU are to work together or not. I worked on a car, where the kid had a Mitsubishi which as a 1993 and he tried to put a ECU from a 1997 in it. It just did not work right at all. Hope this helps and good luck!

Answer
John: Could be a sensor or sensors they explain things to the computer and it sets how things run. I read someplace that you can not replace the computer, other than one that goes with your engine. Because with time things will start to break down. The engine model number is stamped onto a machined pad on the front(radiator) side of the engine block. Your vehicle identification code plate is on the engine compartment firewall. The vehicle certification label is visible in the door jamb after opening the driver's side door. There comes a time when you might have to take it to a shop, it is hard for me to really know without driving and listen to the vehicle. I am sorry I am not more help with this. But I hope this helps and good luck!