Rep Power: 0

A coolant leak will have other symptoms. Low compression, bubbles in coolant tank, coolant loss, coolant in oil.

 
Rep Power: 812

I don't have any leaks. The head install went perfectly, and we used new gaskets for everything. Better than new. Still that rough idle is there. I'm almost betting it's a valve adjustment or something simple.

Would higher compression cause any problems?

 
Rep Power: 283

Do you know EXACTLY what they did to this head of yours?

 
Rep Power: 0

I have an idea....disconnect the battery (overnight)....hook it back up and turn on the car but DO NOT TOUCH THE GAS!!! Let it idle for 15 min WITHOUT TOUCHING THE GAS!!! After your 15 mins are up go driving but drive it hard.....bring it up to 5-6 g's when you shift. Do this for about 15 mins and you will be all set to go baby! 1 peppy Honda Civic for long time!! Those darn ECU's need constant training....they are so forgetful!.

 
Rep Power: 0

You said rough idle. Have you tried torquing the spark plugs at 13ft. lbs? Try to adjust the torque by +/-4% accuracy. Over-torqued or under torque will cause rough idle and poor MPG. This is my 2cents to you.

 
Rep Power: 0

I disagree. The ECU is constantly learning fuel trim parameters and adjusts to the changes in the sensor's tolerance's and performance over time. "Resetting" the ecu should only be done as a last resort or if it is unavoidable due to the disconnection of power. The fuel trim settings and other parameters are kept in memory as long as power is maintained to the ECU. If you have a trouble code which is stored, the best way to reset it is to clear the trouble code with a code reader so you do not lose the learned parameters. Disconnection of power to the ecu restores everything to default values and the car will not be running at optimum until it relearns the original parameters. If you haven't made any repairs before you do this "hard" reset, the parameters will eventually return to where the were before you performed the reset... All the while you are wasting fuel and running inefficiently since the default values aren't the optimum values for your vehicle.

 
Rep Power: 0

^^^^ ok......I was sorta kidding...if you couldn't tell......sorry for making you spend alot of time typing up that response.....muahaaamuahahahahaaaa.

 
Rep Power: 812

I already tried to reset it, and it didn't work. The head has larger exhaust ports, polished, with racing valves. It is also milled 1mm under stock. Now when I turn on the AC and rpms go up a little, the shaking at idle disappears.

 
Rep Power: 0

I thought about this a little more. Your car will run lean if a vacuum line is leaking due to a crack, poor seal, or disconnection. It's very possible that this has happened if your engine has been pulled apart and reassembled. Recheck all your vacuum lines.

 
Rep Power: 0

The ambient tempature has a big effect on power. Along with humitdity and many other factors. Your probably going to find that on cooler days the car runs like a bear and hot humid days it runs poorly. Beyond those simple things thier is a possibility of a lazy o2 sensor that could do that or even an air intake temp sensor.

 
Rep Power: 812

Yeah the humidity is a big problem. It's always humid, but at least not that bad in winter.