Hey everyone, I know a lot of people are having trouble with this topic, but read till the end please, mine seems to be unique.
I have a 96 LX with a cold air intake, bypass valve, and cat-back exhaust. Whenever my car starts cold like in the mornings when I go to work, the RPMs will jump up and then shoot back down and do it again until I put it in gear. I followed the directions on Honda-Tech to clean the IACV and FITV because everyone said that that would fix it. It sounded like a good deal and I was really excited to have my car fixed, but I know the luck I have with my car and sure enough, I still have the problem.
Yesterday whenever I put the car (no matter what the temperature) in Neutral or Park, it would jump RPMs again, now it does not do that and when starting cold (it still jumps) but will eventually idle correctly once it has warmed up.
My friend said it may either be a bad throttle position sensor, or water temperature sensor. I suppose it could also be a vacuum leak? Anyone got any ideas? Sorry for the long post, but thanks in advance!

 

I don't know bud but I have the same prob. It could be ur fitv or tps or vac leek, some even say IAT sensor. Try adjusting ur idle screw. Screw it all the way out till its loose and back in till the butterfly doesn't stick closed and nice and easy. It could be the plug in ur fitv, screw it in till snug and do the tests to c if its the prob, Other than that If u figure it out let me know. I changed the TPS, adjusted the idle, and checked the fitv and everything's good excepted for the idle prob, the only one I haven't checked is the IAT. Good luck

 

It does sound like a vacuum leak. I dont think its the TPS, because it would have the same voltage readings regardless of temp.

 

how are your vacuum lines being held on? it may need a new hose/line or like you said it may be leaking.. small clamps or zip ties should work..

 

I checked the plug in the FITV and screwed it in tight, and also cleaned out the IACV with carb cleaner. It looks really shiny as opposed to all the carbon build up that was in there. I don't get it, which leads me to agree with JDM_DC4_Fanatic about the vacuum leak. Are there any particular points I should check? How does one just develop a vacuum leak, it seems awfully strange to me.
Here's kind of what led up to it.
I'd say about 3-4 months ago I started my car one day and it did that jumping idle thing. I immediatly shut it off and turned it back on, it did not do it again. Probably about 2 weeks later it did it again, and I repeated the process. Then it started to do it more frequently until about this week where it's been doing it every day even when it's not cold anytime I have it in park or neutral.
I guess something kind of important to add to the very first time it ever happened: I started the car with my foot on the gas because it was having trouble starting. When it started it probably hit 4000 RPMs and then I let my foot off the gas, once I had completely let off the gas it started shooting up to 2000 then dropping then shooting and dropping, etc. I don't know what is going on!

 

My vacuum lines are held on with the stock clips I'm assuming, I mean I've never messed with them I don't think. I'll see what my Dad says. I'd rather not have to take this somewhere to get fixed, especially after I did all the cleaning and adjusting on it yesterday after scraping and gouging nearly half my hand.
"You haven't fully fixed a car until you've spilled a little blood"

 

you do not need any type of fastner to hold on a vacuum line. the line should have a tight fit over the pipe, and thats all you need. Vacuum leaks can be cause from hoses not being on all the way, hoses that do not fir tight, small cracks, anything that will let air pass through. There are 2 easy ways to check for a vacuum leak. either spray the vacuum lines with brake cleaner, and the idle will raise up if one is leaking, or use water and spray the brake lines, and the idle will fall and the car will run rough.

 

Interesting, I think I will try that and see what happens. Thanks for the advice. One question, when you said spray the water, you meant to spray them on the vacuum lines and not the brake lines right? Or not? I'm going to assume you meant the vacuum lines.

 

yes, spray either water or brake cleaner. that was a typo on the brake lines....dunno what I was thinkin there

 

My dad checked it out with me. It looks like it may be a faulty MAP sensor? Could that be it, I have yet to try the water or brake cleaner, because it's nearly 105 degrees in MN and humid to be outside. Anyways, so while the car was running my dad unplugged the MAP sensor and the car started a rough idle (but not bouncing RPMs anymore), then plugged it back in and it went to a normal idle, like there never was a problem. That of course triggered the CEL, so I'm driving around with the CEL on for now and it seems to be fine. I'm afraid to clear the light just yet so I can troubleshoot a little more. I do have an OBD2 to USB deal so resetting the light isn't a problem.

 

New O2 sensor and runs great, how would of thunk that

 

New O2 Sensor? Interesting. Well, now I'm confused. It worked fine for a while, then it got progressively worse. I would start it, and it would idle fine, then start doing the RPM dance. Next time I started it, it would be all over the place when it was cold and then level out when it was warm. Now, it does the dance any time it's in Neutral or Park. It's starting to **** me off!

Where is the O2 sensor that you replaced? Is there more than one? I've got a 96 with the OBDII so I'm going to assume there's more than one. Thanks for the help everyone, I really appreciate it.