strange idle issue

[Bowyorang]

Hi everyone! I purchased a 2000 Civic LX a few weeks ago for my son's first car and trying to work some bugs out of it. The car has been fairly maintained and has 224,000 miles.
My issue is that after it has warmed up and in park it is idling around 6-8 hundred rpms then will dramatically go down to 3-4 hundred and back up a couple times. Then will rise up between 1500 to 2000 and back down. Then a minute or so later will do it again. Not always in that exact order but up and down and retuning to idle... anyone have a clue where this gremlin is at?
Also, the idle speed is not always constant. When it is holding a constant idle for a period of time, sometimes it is around 400 sometimes around 6-800. Mostly it seems like a low idle though.
Any help is appreciated!

 

[XpL0d3r]

What's the maintenance history on the car? If you aren't sure, I would start with the basics -- replaced spark plugs, wires, distributor cap, etc.

The car acts fine when the engine is cold? This leads me to believe it's a sensor related issue. Is the check engine light on?

 

[ctag]

Hi @Bowyorang

Off the top of my head that sounds like it could be the IAC valve. I think you can remove it and shake it to hear if it's gummed up or not. If it's stuck, spray some carb cleaner through it and it might free up. Otherwise a replacement from a local auto store is ~$2.

 

[Bowyorang]

Thanks everyone for the advice! Nope, no codes at all.
The only real maintenance that I really know of for sure is what I have done. I had an intermittent stall when I first got it. It had a cracked dizzy cap so I replaced the whole dizzy. May have been overkill to replace the whole thing but I went ahead did it. Wasn't the problem...ended up being the ignition switch. So I replaced it.
I was told by the previous owner he recently replaced timing belt and fuel filter. he thought the fuel filter was the reason for the stall. Other than that all I know is he said that he did regular maintenance and fluid changes on it. I'm going to go ahead and do plugs, wires, ect... it's running pretty good down the road now just that weird idle.
I will definitely replace the IACV and see if that does it.

 

[ctag]

@boofoo I said replace the IACV if cleaning it doesn't work right off.

@Bowyorang With the car off, put the key in and turn it to "on" without starting the car. The CEL should light up and stay lit. If it doesn't, it's burned out or disabled.

My buddy just made the mistake of not checking the CEL works before buying a used car.. Turns out is has bad ignition issues and the CEL was disabled.

 

[Bowyorang]

Ok. Cool deal guys! I'll start by just taking it out and cleaning it to see if that does the job.
As far as the CEL. It does light up and go off when the key is turned on. I did take it to my buddys shop when I first got it to see if it would pull up any codes. He hooked it up to his reader and it connected but with no codes so I dont think it's been disabled.

 

[XpL0d3r]

@Bowyorang

With no load (AC, lights, etc. all off), and the engine fully warmed up, unplug the IACV. Does anything happen?

You will get a CEL for unplugging it though, just a heads up.

Test TPS voltage as well. It should read ~0.45V - 0.50V at idle.

 

[Puffhead]

Hi there! My 2000 Ex had a very similar issue. Mine fluctuated from 700 to 1500 all day at idle. My CEL said it was the IACV. I replaced the IACV, didn't work. Replaced the TPS, didn't work. Then I exchanged the IACV for a new one as it could've been bad from the factory, as per the guy at midas. Boom, problem solved and it's been good for two months. *Knocks on wood*

 

[XpL0d3r]

You would have saved a pocket full of money by just cleaning the original IACV. Sorry to be the sender of sour news.

And avoid ever taking your car back to Midas.

Yeah they're a scam. They claim to have the midas touch. I brought my car there once and it didn't f***ing come back gold.