rpm goes up when in park and accelerate while driving not even pushing gas pedal?

sprayed & cleaned iac. Also rpm stops when ac is on but when i drove it back home yesterday it all started all over again even the ac is on. please help!

Make, model, engine, year, mileage would be somewhat helpful…

If RPM changes but the throttle plate does not move, check for a massive vacuum leak somewhere…

Its a Lexus Rx300 yr 2000,117,000 miles.
I drove it yesterday, same thing happen, jerks and also accelerates.
will have it check tomorrow again. Thank you for the tip.

it was IAC- they change the parts and it works great now…but I have couple of question , the engine light turned on even though they re-set it? so i went to Auto parts store and they were able to re-set it again—but now is back after half hour? what could be the problem??? Any help is greatly appreciated…

Before you reset the light, read the trouble code…Post the code back here…

D code! D code! We need D code. Out of hundreds of possible codes, which one is it?

Got the code print out! P0171 says:
system too lean-bank 1
Probable cause
1.lean Air/fuel injector or vacuum leak
2.MAF sensor
3.ECT sensor fault
4. Faulty H02S(heated oxygen sensor)
Can i fix this myself? or do I have to bring to mechanic again …
safe to drive? Thank you for the help.

Start with trying to find any air leaks (vacuum leaks) to the air intake and intake manifold. Remove the large, black, intake tube and check it for splits. Ensure that the intake tube seals properly to the intake manifold. Temporarily, pinch closed the various vacuum hoses to the air intake, including the brake booster vacuum hose, and the hose going to the charcoal canister, and to the cruise control. Note if the engine rpm changes when you pinch a hose closed.

Got the problem solved-it was vacuum leaks and the bolt wasn’t tighten. THANK YOU ALL–Appreciate the help. More power to CAR TALK…you ROCK!!!