My car Revs up and down but doesnt die???
 

My car is a 94 honda civic 1.5L. Lately it has been reving up and down but if i leave it idling for 5 min it stops and idles fine. But then when I start driving again then at a light it starts to rev the same way. It has never tried to die from it. But there is no check engine light on neither. I took it to a mechanic he didnt know what it was either. anyone have any ideas? Please help me!!

vacuum leak, more than likely...

Very common question. Do a search on this site, and you'll find more answers. Until then, it sounds like your IACV ( Idle air control valve). Coolant runs through it to stablize your idle. Number one thing to do is to check your coolant level. Low coolant level will cause an insufficient amount to flow through it, causing the up and down idle. If that doesn't solve it, it could be clogged. Hopefully it's not. check your coolant level and get back to the forum. There are a few more things you can do, but try that first. :D

I checked all of the vacuums I could find a leak!!
 

the mechanic checked them also.

I just changed the water pump and the water coolent temp sensor. that didnt fix it. the coolant is fine

If your coolant levels are fine, I'd clean it. It's located on the back of your intake manifold connected by two 12mm bolts. You'll have to take the coolant lines off two. Here's a thread of what mine looked like before and after.

https://www.honda-acura.net/forums/s...highlight=iacv

i am going to do that tommarrow
 

Could that be why my car hesitates sometimes? sometimes when i take off it stalls pretty bad and sometimes it run perfect. could that be it or is that another problem?

It COULD be. There are lot of things it could be. Hangout here for a few days. The members here are pretty cool. They'll jump in and give you their two cents. Some guys like to give a dollar fifty, so you'll defiantely go to school about your Honda. :D

Does it always do this, only when your engine is cold?, only when your engine is war?

I had a vacuum leak once, and it only did it when the car was cold. I had already checked the IACV and replaced it with a known good one I had extra and it still was doing it.

But as mentioned, it could be the IACV also...

revs up and down warm cold hot anything before it would just do it everyonce in a while no it does it pretty much all the time unless it is idling for 5 or more minutes then it USUALLY idles good. and it hessitates everyonce in a while too.

I had my P28 ECU stolen, and had it replaced with a P28 from an automatic. The up and down reving came from having an automatic P28 in a 5-speed car. I tweaked the P28 and it stopped. Has your ECU been replaced?

yeahs sounds like ur IACV...

mine use to do that and it was a vaccum leak. lots or searching through hoses solved that one

i cleaned out the IACV it didnt really make a difference when the motor is cold and i start it it doesnt rev up and down for about a min now that is the only difference. any more ideas?

HAve you checked for vacuum leaks?

I have checked. Is there a special way to check? What I did was un plug one side of the hose then plug the hose and the nipple. Is that what your supposed to do?

That could work, but the hose itself might have a hole that you can't see... I sprayed engine cleaner the last time I had one and it was bubbling so I replaced it with a new one :oh: That might be over kill though but it worked for me

Check your fast idle thermo valve. Do a search on how to fix or replace it.

Yeah same problem with my gsr. The fit valve wasnt working properly.

Hey man!!
 

. This is a common problem on Honda motors there is a 90 % chance that the T.P.S is bad which is the throttle positioning sensor which means you need to replace the throttle body,or like the other guy said it could be a vacume leak but more than likely it is the tps.Hit me back and let me know when you figure out what it is.Talk to you later.cy@

--Chuck--

I was searching the same subject except mine roams a bit when warm. anyway someone posted this. I think it will help

http://www.ef-honda.com/ben/Badidle.php

Hey man had the same problem. I cleaned the IACV, did a coolant flush, checked for vacuum leaks, and nothing fixed the odd idle. Today I took off the Fast Idle Thermo Valve, took it apart and cleaned it out with brake cleaner. No more odd idle. At cold start, she idles at around 1200 rpm then as she warms, falls to about 800 rpm. No bouncing idle at all. Maybe that will help you.