okay, bought the car like this. 1998 Honda Civic Ex automatic. Runs fine when first started, idle is a little high. Then, when the car warms up it starts to surge up and down, up and down... sometimes it will just idle really high at like 2200rpm... It had a code for Idle Air Control Valve circiut... So, what I have done this far: I have replaced the IACV with a brand new one from the parts store = no change. Tested TPS sensor = has .5v at closed and 4.7v at wide open. I have sprayed around the TB gasket and IM gasket with ether/starting fluid and got no change. My temp gauge and cooling fan works, so I'm assuming my temp sensor is good. I can put my hand over the TB and it feels like its going to suck me in and the car will die, so no vacuum leaks. I can put my hand over the passage/opening for the IACV and it will just about suck my finger in, but the car will idle just fine then! also, not sure if it is normal or not, but with the KOEO I can hear the IACV humming/buzzing... If I unplug it and plug the old one back in it makes no noise... so maybe the old one WAS bad, because it makes no noise and the new one is making noise so its good??? I dunno whether its supposed to or not. Its really driving me nuts, I dont know what to check or do next...

 

test the temp. sensor

 

how do I do that?

 

there are 3 that are all the same style sensor also... one directly under the dizzy, one to the back side of the dizzy, and one farther back in the rear water neck.... I know one does the fan, one sends to the ecu and one goes to the guage right?

 

when you replaced the IACV, do you bleed the system correctly?

 

i let the car run with the cap open untill I could see all the bubble dissapear... did it a few times. There was no change in behavior from the original IACV to after replacing with a new IACV.

 

After replace the IACV and reset the ECU the CEL light stay off?

 

Is an IACV CEL code still thrown?

The temp sensor that would affect the idle is the 2-wire sensor below the distributor. When the engine is fully warmed up, unplug it and measure resistance across the 2 sensor pins. You should read 200-400 Ohm.

If that's fine, then try adjusting the idle speed as per the service manual - see FAQs sticky.

 

yes CEL still thrown for IACV and Oxy sensor lean condition. I actually just gave up on it and dropped it off at an old guys house that is an auto electrical guru... guys is awesome at this kind of stuff. I will report back with his findings next week

 

P0171? If so, check for an exhaust leak and a clogged fuel filter (low fuel pressure).