I recently rebuilt the head due to bent valves. The temp in Louisiana recently dropped and is in the 40-50s in the morning. When I start the car up, I let the engine warm up before I take off. As I am waiting, the engine spontaneously revs on its own. It would go from about 1200 rpm and rev quickly to 2200. It would repeat this for 1-2 minutes. Any ideas why? It never occurred before in the warmer weather, but once I noticed it got colder it starting doing it.

Update **
I cleaned the iacv a few weeks ago and it seems to have gotten worse. It revs almost instantly where as it used to be after a minute. I also revs for 2-3 min longer than it did before. Also did a map whack and no help. Turning on the ac seems to have an effect but only slightly.

Is it harmful to the car? It is my daily. What else can I do? Iacv was pretty dirty, do I need to clean again?

 

Sticky IAC valve, 100% guaranteed.

 

This^

Classic Honda problem

 

You know, once in a while when I start my S2 it'll rev high ONCE, then go back to normal. I wonder if it's the same issue, just hasn't gotten bad yet.

 

Update

 

My car does that as well I think thats normal. As long as its ONCE at startup.

 

It's more then once. It's keeps doing it for 5 min at least

 

If cleaning the IAC valve immediately made it even worse, that definitely would seem like the cause. Maybe it's time for a new one?

 

I think you may be right

 

You need to take the valve apart with a 5 point torx called a pentacle bit. Once the motor portion is separated from the valve, it will reveal the end of the rotary shaft that the motor pulls around by magnetic force.

Clean the iac with wd40, and spin this shaft with your fingers until the shaft turns smooth 360 degrees. DO NOT TRY TO REMOVE THE SHAFT AS YOU WILL DAMAGE IT!

Reassemble and enjoy your perfect idle.