I have a 98 civic dx coupe bone stock. My car started to idle like as if it were going to turn off but it doesn't. This only happens when I turn on the A/C. I know it's a small engine and I know the a/c takes a lot of power from the engine I can notice it BUT now out of no where it idles low when the A/C is on. Just did the tune up about 3 weeks ago, and I had the car for over a year now. 180000 miles

 

Is the a/c working properly? Condensor fan engaging? Is the compressor cycling too quickly? The A/C compressor draws quite a bit of power from the engine. If the freon level is not right, it will draw even more power than normal leading to a low idle. Get the a/c presssures checked with gauges to find out of there is an a/c related issue that may also be affecting idle.

 

Yes if the fan is not working or the system is overfilled with refrigerant or oil, the compressor has to work at an abnormally high pressure, which draws a lot of hp from the engine.

If it is not that, clean the IACV. When the A/C is on the IACV has to open further to let more air into the engine and keep it at the same rpm.