I have a '96 Civic with 158k miles and am having what I thought was a clutch problem. A month ago it wouldn't start and the problem was the clutch safety switch (done at the shop). A couple of weeks ago a new problem occured. While driving (any speed) the RPMs will dip down to idle level then immediately shoot back up. Also at stop lights during idle, the car has stalled out. I have a theory that it has something to do with improper installation of the safety switch by the mechanic, anyone have any feedback for possible cause?

 

The clutch pedal switch only disables the starter. It has no effect except when turning the key all the way to try to crank the engine.

If you have the engine quit "pulling" and the tach drop to zero while the car is rolling in gear (thus the engine is still turning) you may have lost power to the ignition circuit entirely. Does the speedometer also drop to zero?

 

No only the tachometer drops to zero. In fact on my drive to the shop today, the tachometer was on zero the whole time, but the car drove fine the whole way. i took it to the shop and they ran diagnostics all day and said they found nothing wrong.

 

So to summarize, if you were to never look at the tach, the car always goes OK when in motion, but it will stall out at stoplights.

This sounds like there are two problems: a bad tach, and a dirty IACV.

 

It stalls out at stoplights sometimes, but the bigger problem is while driving and the RPMs drop, the car will jerk for a second before going back to the same level of RPMs.