i am having a problem with my idle. When i first start up the car it some times miss fires, but then is fine as far as running is concerned. but the idle is off some of the time, for instance, i think the idle should be at about 750 - 800 rpms, it idles about there some of the time, but some of the time it idles as low as 550 rpms, but averages about 650ish rpms. i notice that it dives down when i step on the brake, or anything that uses power, so i think the alternator might be going bad. but when i turn the a/c on the idle falls to 550 then shoots up to 900ish then falls again, it does that for a couple of seconds the catches itself. any ideas whats causing this?

 

sounds like a vacuum leak...
or the IACV itself is going bad...

 

Check if you have some carbon build up in your throttle body. Also check your plugs, wires, distrubutor cap/rotor and vacuum lines including the ones around the EGR valve. Good luck!

 

Well its norman for the a/c to drop the idle,and as far as when you hit the brakes it dies,mine did the same thing. Check the line the goes from the booster to the block,or the proportioning valve(the thing where the two lines connect) and if all else fails check the booster it may be leaking.

 

yea I dunno I always thought out cars idle around a grand to 1200 atleast thats what mine idles at. Yea sounds like a vaccume leak

 

its was just an example about the hitting the brakes, another one is if i put the car in reverse the idle drops, or if i turn the rear window defroster on, from what i can tell anything that uses electricity drops the idle, but some times it is completely normal with an idle around 800 rpms i think, but as far as the vacuum lines ill check them.

 

i checked the vacuum lines that i had immediate access to such as, the brake booster, i checked the vacuum lines coming off the air intake.

 

old battery maybe? how old is the battery?
Also, while you are under there checking for vacuum leaks, check the grounds too. If you've grounds suck, then that will tweak with things too...

also, pull the IACV off and clean it out really well. That will help the motor "keep up with itself"

 

ill try it

 

Its your car stick or automatic?