Rep Power: 0

I bought a 98 civic ex sedan back in october from craigslist, guy sold it as it was leaking coolant. when i got it cel was on. anyway, up to this point i replaced the headgasket, timing belt, water pump and reinstalled everything and car runs fine. the issue is at cold startup, the idle speed is anywhere between 1200-1500 rpm and eventually after idling for several minutes, the rpms start to fluctuate, up and down. if i disconnect the map sensor, the issue stops and if i plug it back in, it wont happen again untill i restart the car. the idle adjustment screw is at the stop limit so udjusting the speed down doesnt seem to work. when i run the code I get p0108 for map sensor circuit. is this something i can fix or what is the fix for this. I assume the high idle and it fluctuating after several minutes are related. thanks for the help

 
Rep Power: 518

I think you set the code yourself by disconnecting the MAP sensor while it was running.

Reach in the throttle body while it is surging and cork the large holes with your fingers, see which hole (if any) makes the idle slow down to normal (or nearly stall the engine) and quit surging.

Vacuum leaks or stuck IAC are common.
Cruise control vacuum hose came off?

 
Rep Power: 0

I figured that I probably set the code and most likely that was the code that was in there when I bought it. When you say reach into the throttle body and cork the holes, do you mean plug them? I have seen that this was a common problem in Hondas but couldn't find an exact cause for it. thanks for your help. I will also check on the cruise control hose

 
Rep Power: 518

Yes, with your fingers.


The cause of the surging is always the same: RPM is too high for the condition. But THAT can have many different possible causes.

 
Rep Power: 0

so i went out to the car just a few minutes ago, with it started cold is idling at 1500 rpm, even when engine at operating temp still at 1500 rpm. in the throttle body, the bottom hole which goes to the IAC, if i plug that hole, the car dies. the other hole which goes to the TPS sensor, does nothing. only issue i notice is when the surging happens, if i unplug the MAP sensor, it stops. I check all hoses and found no evidence of any vacuum leaks. the one vent line into the IAC is clear, the other coolant line into IAC clear. starting to suspect the IAC. just curious, what purpose does one coolant line into the IAC serve?

 
Rep Power: 0

ok some other info, when vehicle is in drive, idles at 1000 rpm, only in park does it idle at 1500 rpm. now when the surging started happening, tapping on the IAC did nothing. unplugged the IAC and the long surging went away but started surging veryu rappidly, between 1500-1700 rpm where before it was 1000-2000 rpm when surging. when it surges the cel does not appear. i sprayed the entire engine down with brake cleaner and found no leaks. also the surging only happens in park, does not happen once in drive

 
Rep Power: 518

Concentrate on that. You plugged the hole and it killed the engine, so that means the engine is running on all the air going through that hole.

If the passage leads to the IAC, then your IAC appears to be stuck open.


Only ONE coolant hose to the IAC valve? How does that work? That should have two. Got pics? Your IAC is on the bottom of the throttle body, right?




The valves are supposed to be heated to avoid "icing", that can happen in cool damp weather when moisture freezes as it passes through the valve and pressure drops to manifold vacuum, the temperature drops too.

Icing used to be a big problem with carburetors if someone removed the tube that ran from the exhaust manifold shield to the air breather.

If it had a FICV that would rely on coolant flow to operate the thermal unit that would control cold fast idle.

 
Rep Power: 0

ezone, thanks for the clarification from the picture, I thought the IAC passage on the right that connects to line #1 was a breather line but I see it is a coolant line. so yes then it does use 2 coolant lines. I guess I will order a new IAC and see what happens. thanks for your help. Ill report back once I get the new one

 
Rep Power: 518

I'd probably just take the valve off and clean it, maybe remove the coil and make sure the rotary vane is completely free to move with no obstructions. Then get a new gasket and slap it back on.

 
Rep Power: 0

ended up being the idle control valve. removed and replaced it and idle is now at 1200 for a few seconds at startup then drops to about 800-1000 and runs great. thanks for the help.