just got done putting a new low mileage motor in my 96 civic sedan. installed new time belt, water pump, seals etc, and new radiator, new distibutor ,Clutch, alternator,drive shafts , brakes, fuel filter, fule lines ,brake lines, and much more. so i am anxious to get this thing on the road and driving it. I Am now having an irractic idle but runs fine driving it until pullin in clutch or stopping. I had a iac valve check engine code. i then found that the plug to the iac was not all the way snapped on. thought this was the problem. reset the code and engine is still idleing irratic again???? any ideas. The motor has 60k on it think i need to clean the iac? my guess is that it sat on a shelf at a salvage yard for awhile. luckily they had all the openings plugged off but there may be some dried up stuff in there i cannot see??? I also made sure the coolant was top off good and sprayed starting fluid on vac lines with no change so i know they are good. One more thing? There may be a possablity the thermostat is stuck open because i have never heard my fan come on and the temp always stays low. could a bad thermostat have anything to do with a rough ide also?? thanks for any help i would appreciate it.

 

u installed a lot of stuff, can uexplain in better detail how the idle is acting??

 

Termostat has nothing to do with it. Coolant level and fast idle valve are two things to check first. Yes, I read you topped of coolant. Did you fill it properly, by the book? If not, it could take some time and a few toppings until it settles in.

 

well when cold and first started its fine. idle slowly builds up as engine warms then it will kick down then idle up and then kick down repeatedly.

 

yep, that's what I told you to check, this will cause such a behavior.

 

i also had this problem, i cleaned my iacv valve and it helped a bit, but i also let the car totally warm up, then lowered my idle speed, what might have been happening is the idle was set too high and the computer kept trying to keep it down

 

i bet its your fast idle valve its under neith the throttle body, take it apart and clean it out. Also try cleaning your iacv

 

Problem solved. I took apart my IAC valve to find it stuck. freed it up cleaned and lubricated it and my civic runs like a dream Now. the valve is metal in an aluminum body so i figure that while the motor sat for awhile not being ran that the aluminum and steel corroded a little(as these two metals always do) causing it to stick in one position. I had hardly any cabon build up as this motor was fairly low mileage. thanks for the help guys.

 

it could have been your oxygen sensors, does the same thing (just for future reference)

 

i had already ruled that out before because of my check engine light and installed new but this did not fix the bad idle. according to my manual there are several things that may cause bad idle. i am glad i found it and dont have to worry about it anymore. My manual also said that a leaking or blown head gasket would cause idle problems that was the one thing i am glad it wasnt.