Toyota Corolla manual trans hesitating accelerating... while cruising at about 45 mph and 1800 rpm

At least that’s when I notice it,… right in that range, seems the car hesitates and then starts up again and hesitates,… and you can see the tachometer go up to around 2 k and then down to 1600 rpm,… but I am not accelerating with the gas peddle. Thoughts on what is causing this… the fix and potential costs would be much appreciated.

I assume you mean both the engine rpm AND the car speed go up and down simultaneously, for no apparent reason. Without you moving the gas pedal.

If it’s just the rpm that changes, but not the speedometer, that’d probably be a slipping clutch. But both are changing without changes to the gas pedal?

hmmm … I’d guess either you have an air leak that is allowing air into the intake manifold, bypassing the throttle plates, or the throttle plates are moving by theselves. That could occur if you have the drive by wire feature where there’s no mechanical linkage from the pedal to the throttle plates. Is it an electronic or mechanical throttle linkage? What year is your Corolla?

Two last question. Have you had the diagnostic codes read from the computer? Is the check engine light on?

Mind telling us what year?