My 1995 Civc vx has had a fluctuating idle which I believe is caused by the base idle speed being to high. With the IACV unplugged, the idle reaches about 500-600 rpm before the idle speed screw reaches the stop. I've tried replacing the IACV, TPS, replacing the throttle body, and swapping ECU's. I've also tried cleaning the injectors and the IACV ports. I cleaned most of the carbon from the intake manifold runners when I changed the head gasket about a year ago, and I don't think there are any vacuum leaks because the car dies when I put my hand over the throttle body. Right now I'm thinking that both of the ECU's I have are broken and are what is causing the high idle. I'm hoping someone has another solution so I don't have to go and buy another ECU. Thanks

 

My 92 VX idles high most of the time. Once in a blue moon it actually drops to the 450-500 range it should be at. When it does it feels and sounds like it struggles to run. I have roughly 350,000 Km on the engine all original. The taper is so bad the car sounds like a diesel usually. I personally believe it's not the ECU, if anything the ECU is purposely doing a higher idle to keep it running smoothly. My idle is closer to 800-1000 most of the time. I also had a hard time finding a working IACV. It took me 4 IACV's until I found one that stopped the idle surge. I also have not replaced the O2 sensor. I know the 5 wire expensive O2 sensor of our VX's does a lot more than the typical O2 and I don't know if that plays a role in the idle. I was waiting until I put a rebuilt motor in to see if I still get the high idle issue.

 

My Civic is a California model, so it has the normal O2 sensor without lean burn. I'm thinking that it's the ECU because I'm only getting .5V between the MAP sensor signal wire and ground I think, whatever the white wire from the MAP sensor is, and there should be 5V. The terminals on both of my ECU's I've tried also have .5V between the terminals those wires connect to, so I'm thinking that the ECU is using a different manifold pressure than is actually occurring which is messing up the idle. I might switch to a federal emissions ecu at some point to get lean burn anyways and see if that fixes the idle issue.