Subject: 91 mitsubishi eclipse, . . . help?!
Question:

Hello, was wondering if you could help me with my eclipse problems, here's the story as I described it to amessageboard. I really look forward to your response, thank you for your time,

Hello people, I have a perplexing (to me anyway!) problem and I was wondering if any of you guys (or girls) have any suggestions. . . here's my story:
I recently bought this car and three days later I found out the transmission needed to be reconditioned and it needed a rebuilt torque converter. Also, the car has a Really High Idle, I mean like 3 rpm high, is that right? Anyway this is what's been happening to me in the past month since the car was in the transmission shop:
At first the car was down shifting really hard between 2cnd and 1rst. Then it started upshifting hard between 1rst and 2cnd. Then it started shifting hard on Every shift, and I mean really hard. Finally the car wouldn't downshift into 2cnd! So, I take it to the transmission people and they say its the high idle thats causing the hard shifting and they send me to another mechanic. OK. This mechanic tells me that I need a new air idle switch(or something like that) but he doesnt think thats causing the hard shifting. Then he looks down and sees these green wires that are like cut and he tells me that whoever worked on my transmission last must have done a sloppy job of putting the engine mount back on because these transmission wires were completely cut. So he sends me Back to the transmission people who "fix" the wires and send me on my way stating that the hard shifting has been cured and advising me to take care of that high idle problem.
Ok. So, it did shift perfectly, for about a day, and then, you guessed it, it starting downshifting pretty hard between 2cnd and 1rst. Then it started upshifting hard between 1rst and 2cnd! Now all the shifts are hard again, and we're right back to square one, just without any cut wires to point the blame at. So, and I know this must be getting lengthy so Ill try to wind this down, My questions are:
How could it be the high idle causing this shifting problem if the shifting problem was "fixed" without the high idle being fixed at all. (Is it possible the transmission people did something else to it?)
Also, How could the shifting problem be a result of the wires being cut off when the problem started out small and got worse and worse?
And finally, and most importantly, does anybody have any clue what the real cause of this shifting problem is? Has anybody had any simlar experiences? Does anybody have any advice?!
Id appreciate any advice, immensely, and thanks for your time,
-Rachael
Answer:

Rachel,
I rarely receive a description that so complete. Its good to have for diagnosing this problem. I may have some ideas for you.

There are only two wires I can think of that are connected to your tranny; the back-up light connector and the ground wire strap. It's possible to have strange electrical readings if your ground strap is cut, but I can't imagine that would cause high idle or hard shifting. Let's ignore the wires for now and look at other things.

The 1G Eclipses ('90-'94) were notorious for having sticky transmissions. I've been lucky not to have any major problems with my '90 Eclipse GSX, but I do experience hard shifting. Hard shifting can be caused by MANY, MANY things. There are so many things that can go wrong, and the early Eclipses have the most troublesome trannies. Hard shifting is most likely caused by bad synchronizers. When the synchros go bad, or are install improperly, they don't allow the gears to line up correctly and you can get hard shifting. Another common problem I've heard of have sticking shifting comes from using the incorrect transmission fluid. The common grade most garages use is GL-5 75W-85. Even the aftermarket repair manuals tell you to use it. But the 1G Eclipses are very picky and that grade of oil can breakdown under high temperature conditions and cause sticky shifting. I recommend a full synthetic, GL-4, 75W-90 gear oil. Look for a brand called SyncoShift or RedLine. They make the best I've used for my Eclipse.

Your idle problem is most likey not caused by your transmission problems. If your synchros are bad and your idle is high when you shift, it will be hard to get into gear. But for it not to happen for a while, and then slowly get harder over time, that is strange. 3000 rpms is way too high for an idle. The Eclipse manual tranny models should idle between 800 - 700 rpms. You'll want to check your Mass Air Sensor, Base Idle Setting Screw, the throttle body, and the Idle Speed Control motor . Now, the turbo models (and some non-turbo models) had a bad problem with the ECU (car's computer). The problem was that Mitsubishi put crappy capacitors on the ECU and over time those capacitors will leak, and eventually ruin your ECU. With a bad computer, you'll have all sorts of strange problems

There are a lot of things to check, but my guess is that one or more of my suggestions will fix your problems. I'd also recommend not going back to any of the mechanics you've been to. I usually don't recommend going to the dealership because they're so expensive, but for the major problems you're having, it may be the best thing. At least have the ECU checked by a dealership mechanic. They'll for sure have all the correct diagnostic equipment.

Good luck!