90 Sidekick engine issues

[AndyBees]

Hey, I'm new here. This is my first post. And, there's probably already a Thread on the issue I am about to describe. However, I am doing this for a friend who doesn't have access to a computer nor how to use one. So, spending hours searching for an answer is not exactly what I'd like to be doing.

1990 Sidekick XJ (or is it JX?)

So, having introduced myself and providing some background info, here is the problem: He tells me that the engine goes pop (his words) and then basically only idles. I called it limp mode.

Anyway, he says he sent the computer off for a rebuild/repair and that did not correct the problem. He stated a new coil installed was no help.

Interestingly, he says that most of the time, he can just turn the key OFF and then restart the engine and it does fine.

So........ any ideas as to what's going on with this engine?

[fixkick]

welcome !
that is and odd set of symptoms.
goes pop and all engine power gone, cept idle. very odd.
id say it's losing fuel pressure.
or the dizzy advance if flaky (this car has stand alone dizzy and mech. advance) possible ok , then jams, then unjams ? check advance , when in limphome.

is check engine light on, key on, then goes out , running and stays out, even after the POP ?
make sure the crank bolt is not loose , torque it (17mm) to 94ft/lbs, if loose it may start one time be ok then , it slips and retards and runs bad.