So I couldn't find anything about it in the FAQs, I have a 93 civic del sol with the 1.5 motor, it keeps doing this revving up and down like a vacuum issue. I asked this guy who I used to work with that was a del sol guy, he said it was a sensor under the intake manifold. I don't know him anymore nor does any of my friends that knows him so I ask. Do you know what sensor he was talking about?

 

Fast Idle Thermal Valve. This is a mechanical thermal valve that admits extra air into the intake for a short time after a cold start.

It's easy to check. Take the big intake pipe that comes from the air filter. Note that there are three holes in the side of the throttle body before the throttle plate. The one on the bottom leads to the FITV. Start engine (warmed up) and block that hole with your finger. There should be no air flowing through it. If there is air flowing and blocking it makes the engine slow down to a normal idle, you need to adjust, replace, or block off the FITV.

The two other big reasons for idle surging is not having the cooling system completely full, and problems with the main idle air control valve. This valve is electric and mounted on the back side of the intake near the throttle body. Remove it and clean the passages with spray throttle body cleaner. Also clean the passages in the intake that it mates to.

 

Okay thanks alot I'll try it when it's warm here

 

This is where I would start

 

Replace o-rings while they have it off?

 

I normally do

 

Okay thanks for the advice