90 percent of time no problem, but sometimes when i turn the key u hear the starter start to engage but will not spin motor. shiftng around the gear shift from park to d back to park or nutral. then i can get a start. we bypassed the nutral safety switch today and i changed the starter, and still have the same problem. i sure would like info on these models 1990 300e. is there a relay in the starting system or anything else. any ideas??? i m wondering if i have a bad spot on the flywheel ring teeth.

If you can get it to fail, see if you have the start signal to the solenoid on the starter itself, that would be the Y in the road on the problem.
You could make up a test light so you can see the light come on from inside the car, would be the easiest way to do it but a little tougher to rig it up.

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What were the teeth on the starter gear like when you took it off? Worn?

I'd suspect a bad flywheel gear in that case.

If you bought a rebuilt, it could be bad, too.

I rebuilt starters and alternators at one point in my career. I know they dont do more than basic testing. Gotta keep the productivity up, up, UP!!!

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1984 190E (201 024) 2.3L four.