Idle up and down
 

I have a 98 civic auto with 135K miles. I did a tune-up at 118K miles and
replaced: spark plugs, cables, dist cap, rotor, fuel filter plus other
items.
This morning my car didn't want to start. It cranks, but won't start
(battery is ok). I had to push on the gas (I don't know if it really helps)
but it finally started. After a few minutes of running ok, it warmed up, and
the idle speed went down to the normal after it's warm. But then, I noticed
the idler a little higher than normal, but then the idle goes up and down,
like this: -------_------_-------_
it is about every 4 seconds or so when it drops down for 1/2 a sec and
returns up (sorry, I can't explain it better, but I hope you get the pic).
After that, I drove the car to work, and it did fine, but if I put the car
on neutral or park, it does the same (up and down idle).
Anybody have any idea what could be the problem? when I turn the key to on,
I can heard the main relay clicking twice as normal. Also, I filled up the
tank at the normal place 60 miles before this problem happened.

Thank you for your help.