Hello, first post. I know that idle issues appear to be a common thing, but what happened to me does not fit anything I have found.

I bought a 1999 civic ex with over 200,000 miles for fuel economy. The idle was a little high at 1100, so I followed the procedure for how to set it. However, I disconnected the MAP sensor by accident instead of the IAC. Well, when I plugged the MAP sensors back in the idle jumped to 2000 and was surging 1800 to 2200. I was like WTF. This is when I found out the car does not have an operational CEL. I pulled codes and it had a 1509 and 122. I do not know if these were present earlier. Did a bunch of trouble shooting, cleaning the IAC burping the cooling system all to no avail. So I went online and got a whole new TB with all sensors off a junked civic that had been hit (so I assume it was running when it was junked). I cleaned this up and put it on, the idle now sits at 1600 and rapidly cycles between 1550 and 1650 and it only has a 1509 code. I disconnected the IAC, nothing changed. I pulled the IAC module off and played with the valve shaft and got it to idle solidly at 1000, then as soon as I put the IAC module back on (not plugged in) it starts hunting again. Any help that you guys can provide would be appreciated. I just really do not inderstand how unplugging the MAP caused this. Also, have used ether to check for vacuum leaks, but there are none. Also, if I block the front passage in TB just above the butterfly, the idle will drop to a steady 900 or so.

 

Hope you didn't waste much buying the throttle body.. If your covering of the port is lowering your idle and holding steady, then possibly its just the IACV as your culprit. Cleaning them never really does much because of the age and wear. If theres seals inside of the body, maybe they have hardened or deteriorated. Never needed to take one apart to see the guts though so I'm unsure what's inside them.
One other thing I was thinking that might help a little was, check your pcv valve to make sure it's not getting stuck open a bit too. Could try cleaning it out or they are cheap to replace.

 

Thanks for the feed back. I only spent $54 shipped for the TB, so not bad.



Something else I would like to note, if I leave he car in gear (its a manual) and coast down, it starts bucking really badly at this RPM. However, if I use the brake and force the car through this small RPM range it smooths right out until I finally depress the clutch, then it jumps right back to 1600 and starts hunting.

 

hello sir. was kinda bit curious, what OBD scanner / reader are you using? we have the same problem though. i have replaced the IACV but to no avail. now im going to look at the PCV valve.

 

It was a reader I borrowed from a friend, don’t remember the make.

I chased and chased this all to no avail. I replaced the TPS, IAC valve , PCV valve and even a new to me (used) throttle body. The only way I was able to get it to stop was I took the IAC valve off and filled with RTV, thus rendering it inoperable. Then I tweaked the idle screw (the one on top that is essentially a controlled vacuum leak, not the throttle body butterfly screw) until it would run well cold and warm. I had stumbled across something that said the computer may need replaced, but I was not about to drop that kind of $$$. Sorry, but that was all I was able to do.