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2000 Ford Focus ZX3 DOHC. Got the A/C system fixed by a local mechanic months ago. Told me that he changed out the compressor & condenser. After the car was brought back, it began to have idling issues causing it to sputter & occasionally shut off whenever the A/C was on. I was told that the IACV was probably the culprit, so I changed it out w/ an aftermarket one from Autozone. After doing so, a new problem arose: I now get high RPMs upon start-up. I assumed it was the car warming up to the cold weather, but whenever I'm driving, it still occasionally revs up to 2.5k RPMs as if it needs to shift up. In addition to this, the RPMs sometimes remain the same even when I take my foot off of the gas, & car continues to speed up. If I start braking, the car fights back & jerks. Upon a complete stop, jerking continues until the RPM finally plummets to <1k. If it helps to mention, the car sat undriven for over a year before I got it from its previous owner. Thanks for your time.

My car has 77000 miles.
My car has an automatic transmission.

The first thing to check for in any drivability problem is air leaks. Any air that gets into the engine without being measured will lean out the system and cause problems. Look at all the rubber hoses and boots under the hood to be sure they are well connected and in good condition. If the check engine light is not on, it probably should be. Turn the key on without starting the engine, the CEL should be on. This is a bulb check feature. If the stays on after starting it means there are trouble codes stored that can help in the diagnosis. These can be read by a technician with the appropriate scan tool. The other likely source of trouble is the throttle body. It’s common for there to be a buildup of carbon and varnish on the sides of the throttle body that can in interfere with movement when the throttle is closed or nearly closed. This can usually be cleaned out with a good solvent. To have this done for you at your convenience, you can contact YourMechanic, they can send a technician to your home or office to check out your rough idling Focus and let you know what can be done for it.

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