Hi everyone, I have been lurking for a while here and this is a great forum!
Okay, so I have a '95 EX Coupe, 1.6l, 5spd., and I have the dreaded fluctuating idle problem. I have, one at a time, disconnected the O2 sensor on the exhaust manifold, brake booster (plugged the port), fuel pressure regulator (plugged the port), and idle air control valve, but still get the fluctuation. It fluctuates from ~1,000 to ~1,250rpm, up and down over the course of a few seconds for each interval. I have no vacuum leaks as far as I can tell. I changed the PCV valve and this helped greatly (it used to rev from ~1,100 to ~1,500rpm before this), but did not cure the problem. Incidentally, when driving at a high steady speed (like driving on the freeway) with the engine cold ONLY, the CEL light comes on and gives a 'fuel pressure' code. I don't know if this is a related problem or not. Here is the weird part: if the idle is fluctuating, sometimes I can tap the gas pedal, bringing the rpm up to 1500-2000rpm and a few seconds after coming back down the idle will return to a steady ~700rpm or so and not fluctuate anymore. I can drive the car for a few blocks and then the fluctuation will return. Tapping the gas pedal doesn't always stop the fluctuating idle. I'd say it works about 65% of the time. Would this be the throttle position sensor? I haven't had time to test it yet. Any ideas? Thanks for any help!