rough idle after warm up

[fourreel]

'93 Si starts up nicely and sits around 1500-2000 rpm until it warms up and then drops off to 500 rpm and pops and sputters. I gave the dealer $45 to tell me to check valve adjustment and fuel filter (not too impressed with them). Valves were fine and I'm not going to bother looking at the filter because it runs great under accelleration and at highway speed. If I'm coasting to a stop, it runs pretty well and idles at 800-900 rpm until I stop (rough idle after I stop). Is it possible that there is a coolant sensor giving me grief... cat converter heating up causing problems? O2 sensor was replaced when I had to replace the header due to cracks. thanks

[CivicSpoon]

Well are you throwing any codes? Have you played with the Idle screw on your intake manifold (or maybe it's on the throttle body can't remember at the moment)? Could be a damaged O2 sensor from when it was replaced. Any over heating issues? Maybe you should check the filter, my oldsmobile had trouble starting and idling when the filter was going to shit; couldn't hurt to check it out at least.

[JoeC#3]

my brothers 90 civic did the same thing with the o2 sensor went, but he told me on the 92-95's there is a second sensor on the cat. im not 100% sure its there just what he told me. I just replaced mine 1 week ago but b 4 i did the check engine light wouldnt come on untill it heated up or i stomped it. If there are 4 wires going to the sensor then there is a heating unit that sometimes goes bad.

[hundahunta]

I would check for a vacuum leak.