Geo Prizm / Toyota Corolla slipping into neutral

My wife’s 1995 Geo Prizm / Toyota Corolla has a bit under 104k miles and recently began exhibiting a very intermittent problem (which oddly has so far occurred only when she’s driving it!)

While cruising at moderate speeds (40-50 mph) under light throttle, the transmission seems to “slip” into neutral. The first time it happened my wife thought she had accidentally bumped the gearshift into N (which is possible on this car) but looked down and verified she had not. After coasting to a stop at the side of the road, she shifted into neutral, then back into drive. The transmission responded and she drove the rest of the way home.

About 4 months ago at ~100k miles, we had some preventative(!?) maintenance performed on the car which included transmission fluid and filter change. Prior to this, the trans fluid appeared to be in good condition and was filled to the proper level. After this 100k mi. fluid and filter change (I verified they used the correct fluid) the fluid level was very SLIGHTLY high – maybe 1/16" over the high end of the “hot” range when the vehicle was warmed up. No foaming or frothing that would suggest that the very slight overfill is a problem – as far as I can tell.

Last weekend I performed an oil change on the car and replaced spark plugs, wires, dist cap, and rotor. I can’t see how any of that would have affected the transmission, but it was just after that the problem happened the first time. (No, I didn’t leave a wrench anywhere…)

A quick Google search yielded the following similar problem, but no one appears to have responded. http://www…72637.html

Any thoughts or suggestions?

CLARIFICATION: I should have said the car seems to slip into neutral. I don’t know for certain that it did slip into neutral, but my wife said when it happened the engine revved and there was no power to the wheels – exactly what would occur if the transmission suddenly went into neutral.

I drove the car around for 20-25 miles right after that, and then drove her car to work the remainder of the week, but was unable to reproduce the behavior.

Assuming your car has one, the shift cable may need adjusting. There is usually a procedure for this and it is not difficult. Someone on this forum probably has the information. You may need someone to help you.

Okay, I’ll look into it. (The maint manual I have for the car does have a section on shift cable adjustment, but I forget which model years it applies to.) Thank you!