When i start my car after it's been sitting overnight or like 4 hours or so, it surges at idle for the first 45 seconds. It goes from about 1k to 2.5k, and after about 45 seconds of sitting it stops surging and slowly goes down to a steady 650RPM (normal). If I start driving right away without letting the engine warm up, it doesn't surge while i'm driving, and after i start driving it, it doesn't surge even when idling. The IACV IS clean, with a new screen filter and seal/double o-ring.

To make clear, it only does this surging at idle, and only right after it's been started. After that, no more surging until the next cold start.

Sound normal? It doesn't really seem like a big deal as it goes away pretty quickly, and the engine runs just fine.
Just wanted to get a second opinion.

 

I have moved onto a 4g63 turbo after my civic was stolen and I always get idle surge on startup at idle when it's warming up. No big deal. Just your car trying to warm up.

 

No CEL?

First check whether the coolant level is low, and then try bleeding the cooling system of possible trapped air.

You also could have an intake air or vacuum leak. Carefully check the hoses and connections.

 

nope, no CEL

radiator is topped off, overflow reservoir is at MAX.

i'll check the vacuum hoses though. i suspect there isn't a vacuum leak though, because when i removed the brake booster line to suck up seafoam, it had a noticeable change in idle, which would seem to indicate that the vacuum lines were sealed prior to me removing the brake booster line from the IM. I put the booster line back on of course. Oh and, it was doing this surging thing before I did the seafoam.

 

Even with the radiator and reservoir topped off, air could be trapped in the cooling system. Bleed the system by starting at step 9 in the diagram.

I would not expect a possible vacuum/intake air leak that causes a transient idle increase to eliminate total vacuum in the system. Also consider leaks around the rubber seals of the FITV and EACV, the hoses and connections for the PCV valve, and the gasket for the throttle body. You might try spraying some carburetor cleaner around those components to check for a change in idle speed. Keep in mind that the test must be done when the engine is cold as I suspect that heating of the engine leads to expansion that closes the leak.

 

i'll try bleeding it, but i also doubt that it's the problem because i changed the radiator fluid, hoses, and thermostat; and bled the system in June when I got the car.

 

I thought this was normal for 4 cylinder engines. Dont they rev up higher at first to warm up the engine faster?

 

Not absolutely sure, but 2.5k rpm seems too high. I think 1.5k rpm sounds more normal, especially in the warm weather of Florida.

 

on my 95 lx and my 99 si, on really cols winter days it would go to about 2.5k. Then when the engine warms up a bit both cars would rev down by themselves

 

Oh, also be sure to slide the heater lever to max heat while you run the engine in step 10.