Why is my idle running high(about 1500 rpm) and sometimes it goes up and down ?

sounds like a bad throtle position senser or a vacume leek.

Thanks for the reply. How much do you think it would cost to repair either problem ?

Probably under $150 depending on labor rate and diagnosis time involved.

it may just be the automatic choke, does this happen on colder days?

wow, ok. well its your fast idle thermo valve. its full of carbon. just take off your intake tube and there is a hole on the bottom left. clean out that hole with carb cleaner and maybe some intake cleaner and keep your car running manually or it might die. then let it run for about 10 or 15 and you should be good. otherwise you need a new one

Idle air control motor are notorious for messing with the idle speed happened to a buddy. Easiest solution junkyard little time and 20 bucks. Cheapest way to try to resolve the problem if you need a new one. I call it an Idle air control motor the post above may be the same thing.

it's your O2 sensor

Make sure the coolant is full, Hondas can have surging idle speeds if the coolant is too low.

My 1999 civic lx is running at 1500 rpm while parked. Changed the idle control valve and it ran good for two days , I replaced a bad alternator and when I drove the car it ran steady at 1500 rpm . Any suggestions?

any idea where can I bring the Honda city lxi for the rpm dropping....at auto shop...

My car idles to high what can I do to slow down

I have a 99 civic lx. Had the same problem. I got a bottle of fuel system cleaner which I put in my gas tank and then filled it up. I drove the car around a few days and its all cleared up . My civic is now idling 600 rpm.. I have also stopped buying the cheap gas. And only use permium 91-93. Strangely the car runs smoother and faster. I have been using the same fuel system treatment every 2 months on a tank of gas My Civic runs like new no check lights. Also change your air filter at least as scheduled.