you come to right place here

there is an '89 manual link and it should be the same as 91 (or close) look for the name "MontyMcV" and in his signature is the link

the computer will show some codes..if it is working or not

but what other information can you give? (did you just wash the engine at the car wash, ect?)

1989 5 door montero 3.0 auto
stock original Japanese
about 200k miles