Rep Power: 0

Ok guys my '98 civic ex has been idling really low for a long time.After it warms up it wanders within 200-700rpm for awhile then eventually settles around 200rpm. I have thoroughly cleaned out the IACV and throttle body and replaced the PCV valve. All this definitely helped as the idle does not seem to wander as much and it doesn't get so low it dies. However it is still idling lower than it should and I am wondering what I should do next.

I am not getting the check engine light but is it possible one of the O2 sensors isn't functioning properly?

Is it possible the IACV is just bad and I need a new one?

Should I adjust the throttle screw? I was under the impression that when idling the throttle plate is supposed to be fully closed so all air flow passes through the IACV. Opening it up would increase idle but I wonder if it would actually solve the real problem.

All suggestions appreciated!

 
Rep Power: 0

I would try the screw, but follow the proper adjustment requirements, there is a certain procedure.

 
Rep Power: 811

everything is electronic and you should not have to adjust any screws. do the idle learn procedure first by disconnecting the battery and letting the car idle for 10 mins after warming up. if the idle is still too low, or fluctuates, it may be a small vacuum leak or a broken iac valve. if you unplug the iac connector, does the idle go back to normal?

 
Rep Power: 0

Check for vacuum leaks first. You can check by spraying throttle body cleaner along your vacuum hoses... if the car revs or reacts.. you've got a vacuum leak... just replace that hose and you're golden...

worst case scenario.. your Throttle Positioning Sensor (TPS) is bad..
this is a worst case scenario since it's actually attached to the Throttle Body.. Which brand new list price from retail stores is about 349.00$ You can find a used one for cheaper... but be weary of used sensors... since... even if they are good at the moment... they're the same age as your bad one.. =/

also.. try new spark plugs, plug wires, distributor...
check your spark plug housing for oil... could be a bad valve cover gasket or grommets, causing oil to leak into the housings... this would cause your plugs to over-arch and foul out.. which would make your engine miss and idle like hell...

after each trial by fire here... reset your ecu (disconnet the battery, or the battery fuse [fuse #1 in the box under the hood.] for a few minutes fuse #1 in the box under the hood.) and do the idle relearn.

 
Rep Power: 0

You cleaned the IACV but did you check if is working? It is electronic as well as mechanical. If you cover the IACV opening in the throttle body you should feel a strong vacuum if you just started the engine. If you don't then the IACV is probably closed and not working. Another test is to unplug the IACV. If it is working the idle should drop. For High idle conditions unplugging the IACV will not drop if it is stuck open.