I've been having a problem with my cars idling. I have a 1996 Honda Civic DX and it is slightly modded with CAi, headers, and exhaust. When im driving down the road its fine, but when i come up to a stop light or w/e and i push in my clutch and start slowing down the idle goes from 1500 rpms to 800 then back to 1500 and down to 800 over and over. But when i come to a complete stop the idling stops doing that. Someone suggested that it might be the IAC. What do yall think?

 

More probable reason would be low coolant level or improperly done coolant change.

 

what does the coolant have to do with the idle?

 

FICV (Fast Idle Control Valve) operates off coolant temperature. It is located high enough to develop air pocket with the minimal drop of the coolant level or because of improper filling. This usually gives oscillating idle during cold start, but I've seen your symptoms, too.

 

chk for a possible vacc leak..........and make sure the base idle is ok..700 rpm ........if base idle is too high engine will surge

 

i have this same problem, however i have an automatic. It just started acting funny today, and after adjusting the nut for the tension of the throttle wire, it will start up at 1500 then go down to about 800, and when i rev it up a little it will stop back at 1500 for a few seconds and then go back down to about 800. Still think its air in the coolant? or could it be a sensor?

 

Could be a number of things including low coolant, and low coolant is the easiestto check and fix, so it makes sense to start here.

 

haha, yeah i checked the coolant, its full. i played around with the throttle line a little more and got everything to work.

 

i have had this happen before as well and it wound up being my idle adjuistment screw which had backed its way out of the hole which all i did was ruff it back in untill the idle sat at 700 rpms

 

a bad PCV valve can cause improper idling. might want to look into that also. they are only 4-5 dollars from a automotive store. just my 2 cents.