Maybe try your Throttle Position Sensor, have same problem and am currently waiting for the delivery of the sensor .. will let you know if it works for me, then you can try it

 

oh and my engine light is always on now...so im thinking it is the IAC valve (edit: SO MUCH MONEY!!=MADDNESS!)

 

behindthe drivers side kick panel is your ecu. there should be a grean harness with a plug with two wires. use a paper clip and jumper the two wires. turn the key to run. if it flashes code 14 its the iac it should flash once for like 2 seconds then 4 times quickly. if its a dif. number, the codes are on here somewhere use the searh key and youll find em.

 

You will get a constant CEL and code 14 if the ECU detects the engine idling too high for any reason. The ECU has limited information to go on, it only sees the idle speed is too high even with zero drive to the IAC. Getting a code 14 does not necessarily mean the IAC is bad.

 

Im having the same problem on my car, the code on my car came up a code 14, so I did buy a new IAC and put it on and the code is still commin on, Ive been talking to other people and they say it might be the MAS or the Trottle body it self. Im in the same problem your having, so take time and be sure it is the IAC, I had mine tested and it came out good but i still bought a new one and its doing the same thing still. So before you add 300 to the car make sure, I added bout 180 with out labor and it still didnt fix the problem?

 

I took it to my mechanic today. I'm waiting for his call to let me know what the problem REALLY is. I will update the information as soon as possible. Thanks for the help so far guys, really appreciate it!

 

good point its not always the IAC my bad, i changed mine 3 times and it was a vacuum leak. i was pretty pissed. but owell its fixxed now good luck with fixxin it i know what its like to have ****ty idle. good luck

 

I think its the idle control valve on the back throtle body. I had the same issue on my 1997 civic DX coupe. I idles fine until the car reached operating temp then idles up and down every few seconds.

 

Here is a link to thread that I created when I was having the same issue. It took me about an hour to replace the valve, it is easier to remove the throtle body to replace the valve

 

Sorry:

https://www.hondacivicforum.com/m_441863/tm.htm