Hello i live in phoenix, arizona. It gets well over 109 degrees out here and it gets very very hot. I got a 98 civic Dx. And my problem is when I have the ac running for a while and then turn it off my rpms shoot up. It feels like the car wants to shoot forward so I'm slamming on my brake. But when I turn on my ac the rpms go down and the car better but it shoots up some times. I go around 25 mph when this happens with the air off not pressing the gas. I can put the car into Nutural and the rpm just stay up. I have no idea whats going on even when i get out of my car and mess with the throttle cable the rpms still are high. I have no idea whats going on. Please Help

 

Make sure the throttle cable is slack when you're not pressing the gas pedal. Then clean the IACV and if the problem continues go thru the idle adjustment procedure which will lead to closing down the air screw.

Could be a vacuum leak such as the throttle body not securely attached to the manifold, manifold not secure on the engine, or a bad brake booster, PCV hose, etc. Pinch off the hoses and see if the rpm drops considerably.

 

Is the CEL ON?

 

the cel isnt on and it only happens when my air is on and its hot outside. I cant figure it out. can anyone help figure it out kljagohsaguohg.

 

When that A/C is on, a signal is sent to the ECU, which then signals the IACV to increase idle speed in order to compensate for increased engine load. The ECU is either receiving erroneous signals or sending erroneous signals to the IACV or the IACV is not responding correctly to the signals.

Start by cleaning the IACV as mentioned by mk (see forum DIY). If cleaning the IACV doesn't solve the problem, use a multimeter to troubleshoot the ECU as described in the diagram: