Subject: Mitsi Galant Viento spluttering
Question: I have a 1990 Mitsubishi Galant Viento DOHC Automatic. Has been purring like a kitten for 5 years with regular maintenence. Has developed a sputtering under 3000 rpm during acceleration after adding STP Fuel additive to a full tank to clean jets. Have replaced spark plugs which has restored a large portion of power during take off. This has improved the problem when the car is cold but still sputters when hot when accelerating. Have also noticed the trans a bit jumpy between 3rd and OD and has not been able to mesh into 4th from 3rd (ends up in a neutral) when going up a reasonable incline at speed (has done this once or twice). Trans fuid is clean and full. Any help would be appreciated.
Answer: Simon,
The early model Galants are notorious for having sticky transmissions.
And with your particular year, it may be an electrical problem. Take a
look at this article. Even if it does not apply to your problem, its good
to know:
http://90gsx.com/eclipse/cap/caps.htm

Have your ECU checked along with these other presumable causes:
1) Improper adjustment of kickdown servo and/or switch
2) Malfuntioning of kickdown band or piston
3) Malfunction of valve body
4) Malfunctioning of ignition signal system
5) Malfunction of transaxle control module (TCM)

These possible causes are taken directly from the factory service manual. Have your car inspected at a transmission specialty shop. Your average mechanics garage may not have the knowledge set or tools to handle this job. Plus, it will probably be less expensive than going to the dealership. But whether you take your car straight to the dealership or a transmission specialist, bring the list of causes I mentioned. They will most likely be impressed and not over charge you to looking at
" everything" ;-) Also, don't forget to have your ECU inspected as well.
That may very well be your problem.
Good luck!