ok so i was driving home today from college. crusing down a country road in the rain at bout 60mph. the defrost was on and the wipers going. i noticed that my rpms would rev up about 500rpms really quick out of the clear blue. just like u were sitting and ideling and taping the gas. no idea what would cause that. it hasnt done it before or at least i havnt noticed it before. i have a 98 3.9 v6 with a flowmaster 40 on it. anyone have ne ideas of what would make the engine rev up like that? it only seems to do it when im at 60 or a little above.

 

possibly a throttle position sensor (tps) problem?

 

500rpms seems a bit extreme, but when I had my cruise set for 95ish going across Montana back in 98 (when reasonable yet prudent was still the speed limit) if I turned my AC on the clutch engaging would make the car shudder. Perhaps it's your AC clutch disengaging or something of that nature.

 

it doesnt seem to do it when the defrost is off.

 

od on/off switch, this car my girl had did that all the time bad wires though

 

defroster overdriver? hehe

 

X2 on the TPS. you can try unplugging it and hitting it with electronic cleaner first if that doesnt work they are real cheap and easy to replace.

 

its the a/c compressor that does that....when you are in defrost....the compressor actually is on though you put it in heat.......anyway its somewhat normal for it to jump bout 5-600 rpms..........same thing happens on my dak......