problems with idle

I just bought this 95 Eclipse that has a 4cyl non turbo and know nothing about these types of cars. Anyway, It's been having idle problems. Before this had it in the shop did something simular but it was the fuel sensor and wouldn't run at all.After it was fixed ran fine for a few days. Then it was running fine and I shut it off. Came back to start it and I had to keep my foot on the accelerator to keep it running. Had a mechanic look at it and he adjusted the idle. Well now it revs up and revs down on its own. Plus the check engine light came on too. Does anybody know what might be causing it? Thank you

have your egr checked out if there is carbon built up those are the syptoms

Welcome to AF.

You're best bet is to take the car to AutoZone or some place that checks the CEL and see why it's on. That should lead you right to the problem.

On the 95 non-turbos (420a motor) there is no idle adjustment. It's all controlled by the computer (ECU) and none of the sensor on the throttle body (or anywhere for that matter) are adjustable. That's why I hate mechanics.

Since the idle is bouncing up and down, it could a couple different things. The Idle Air Controller (IAC) could be going bad or have dirt built up on it, causing air not to flow properly past it. There's ways to test the resistance.

You may also have a vacuum leak somewhere. If you open the hood while the car is on, listen for any spots where it sounds like air is leaking in/out. The small rubber hoses get brittle and can crack over time.

There's also a couple other things too, such as the EGR valve, O2 sensor... but you're best bet it to find out what the check engine light is and go from there.