22nd Oct 2002, 15:08

I have a 1990 mighty max 4wd pickup. I bought it with 242,000 miles and I have added it up to 263,000 miles so far.

I recently have had a problem with the motor jumping up to 3000 when I start it up and while it is idling. I've tried fooling the computer by disconnecting the idle air control and the throttle positioning sensor. All of this is done by disconnecting the battery cables for about 15 seconds.

My mighty max is a very reliable pickup now (except for the idling problems). So far I have changed the alternator, battery, cap, rotor, plugs, wires, intake gaskets, valve cover gaskets, lifters, valve stem seals, transmission, transfer case.

I have also wondered if anybody knows if the water temp sensor might have anything to do with my idle problems? If anyone has any ideas please help.

17th Dec 2002, 08:18

I have a 1988 Mitsubishi Mighty Max, my granddad has a 1990, and my uncle has a 1989 4x4. My uncle is the one that got us started because he got his and bought about 10-14 for parts over a years time. We discovered that on the speed odometer cover there is a cap type plug opposite side of the hazard switch. If you remove that cap there is a small switch that connects to the speed odometer if you switch it the check engine light will go away.

3rd Nov 2008, 10:46

I have a 1991 Mitsu Mighty Max.. Bought it used smogged and tagged. The thing runs good. I replaced idler arm, new alternator, battery, mostly all hoses. So now my clutch cable snaps. I bought a new one and is about a1/4 to 1/2 inch bigger? I asked several diff parts stores and it is the right one. Long story short I have to jimmy rig it to keep the right tension.. But it snapped again does any one know why I don't have tension?

17th Aug 2010, 00:34

To the guy with the clutch tension issues, I just got a 1991 Max 2.4L, it runs good, but I too just replaced the clutch cable and had to put a 1 inch spacer in mine to take up that space you talk about. It shifts better now. My alternator took a dump today so payday has got to get that plus a starter, and plugs.

9th Sep 2010, 21:19

I have a 1991 Mighty Max 4X4 3.0L. Awesome little truck! 189,000 miles. Sat for 5 years in the woods; rats got in the air cleaner, cleaned that out, ECU went bad, got a new one. Valves went out about 100,000 miles. In the process of fixing them. Only thing done except the valves and ECU are routine maintenance.

12th Jan 2011, 12:25

I bought my Mitsubishi Mighty Max p/u 4x4 V6 with 42 miles on it in Jan 1990.

I now have 248 thousand miles and need to get the bluish smoke to stop. It needs a valve stem seal job I think.

It drives like the day I bought it new. I just did the top end again and the engine is beautiful. I cannot part with this truck. Cannot decide to have a rebuilt put in or do the valves.

Any suggestions?

31st Jan 2012, 16:03

I have a 1992 Mitsubishi Mighty Max, and it runs absolutely great with 150k miles. BUT, it won't idle when it's warm. I basically have to keep the RPM's up to 1000 with the gas to keep it going. Once it goes, it goes great though. Does anyone know if I just need to adjust the throttle cable, or is this bigger problem I need to figure out.?

17th Nov 2012, 21:28

Replace with a factory cable. I had the same problem with one from Autozone. So spend the extra 20/30 bucks; it's worth it.

14th May 2016, 00:21

I have a 1989 Mighty Max with 130xxx original miles. My dad just gave the keys. It has been sitting a while, but was last started 3 to 4 months ago. My problem is the accelerator will not move at all. Wondering if y'all have any ideas. FYI it's my first vehicle with a carburetor.