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.
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(This isn't an answer to your question, unfortunately, but...)
My 1990 Civic LX is doing the same thing, except mine starts OK. I will be sitting at idle, the tach will be around 1K, and all of a sudden it starts going up and down between 1,000 and 1,500RPMs. Usually O2 sensor failure does this, but I replaced my O2 sensor with a brand-new Bosch O2 sensor and the problem still exists. It's also really "jumpy" in the lower RPM range. If I am in any gear and the tach is between 1,500 and 2,000 RPMs, it "lunges and lags" rapidly, as if I were tapping the gas pedal quickly, but of course, I am holding the pedal steady only about of the way down. After it clears 2,000RPMs it levels out and acceleration and engine operation returns to normal.
(1.5L Dual-Point Fuel Injection; D15B2 engine)
Jonathan

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K-town wrote:

You may want to check that the cooling system is full and bled of air. With the engine cool open the bleeder valve and top up the cooling system if it's low. Coolant should flow freely from the bleeder valve once all of the air is out of the system.
Eric
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Ron wrote:

------------------------
Your no-start is caused by a flooded engine . . that's why the 'how to start a flooded engine' trick worked. See your manual about 'starting the engine' You probably have one injector sticking open, flooding the engine over night. Injector cleaner or Gasohol might fix it (see manual if you don't know what gasohol is). You didn't mention whether you checked your rad or your reservoir, but probably one of them is LOW. The sensors in your cooling system have to be immersed, or they will give flaky input to the computer, and idle will go goofy.
'Curly'
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Ahh... I wondered why low coolant makes the idle irregular. That makes sense now.
Mike
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Based on what "Curly" said, I'm 95% sure that's the problem with my car. I've changed the throttle body on my car, so there probably is some air in the cooling system. I've noticed the temp needle jumps up and down too. I'll bleed the system and see if that fixes it.
Thanx! :-)
Jonathan
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In addition to the other answers do a google search on main relay problems in Hondas.

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