Baffling... sporadic but frequent problem: 2002 Civic EX, manual trans, 110,000 miles. Often when A/C is switched on, the engine surges between 300-2000 rpm at idle, sometimes stalling. When this happens, the A/C is not cooling - fan is on, but not cooling. No surging occurs unless the A/C is switched on. Sometimes all systems work fine. Can't cause the problem show up. Neither Honda dealer service nor an independent shop has been able to diagnose. Maintained in great condition other than this problem. Any clues, anyone?

 

While it is acting up, check that both fans under the hood are running. If the fans don't work, the A/C condenser in front of the radiator will overheat, leading to over pressure which bogs down the engine.

If you can press the gas pedal slightly and have good A/C performance, with both fans running, clean the IACV valve on the intake.