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.

 

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

 

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.

 

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...