This happens to my car once and only once, once a day, Everyday (confused yet!).... I start my car in the morning after it has sat all night. I begin driving and the first time I have to come to a stop (be it 1/4 mile down the road or 5 miles down the road) once the car stops completely, the rpms drop to 600-700, stutter for a breif second, then go back to normal (about 900). From there on out, the idle is fine the rest of the day...even after sitting 8-9 hours at work.

Since it is basically impossible to recreate for a mechanic, I'm not sure what to do-

Any ideas?

 

If there aren't any fault codes (you didn't post any) take off the hose going to the throttle body and clean out the valve with some carb cleaner and wipe off all the carbon. Change your air fiter and clean your MAF sensor while your in there.
If that doesn't work get another can of carb cleaner and spray it down the intake of the car while someone is flooring the engine, that should clean out any carbon builup on the intake valves.

 

i have kindasamething, but when i start engine inmorningwhile pressing brake sometimes it even dies, serviced car2 month ago, or is itsomething else besides dirtyvalve?

 

I think its just a coincidence that when you hit the brake pedal the car dies in the morning.
Possible causes of hard start issues like that are a faulty CTS (coolant temp sensor), leaking injectors (which aren't common), or a restricted air flow like a really dirty air filter or carbon build up in the intake.

 

i've noticed if i release brakesrpm rises just enough to keep running(400-600) for about 3 second and then all the way up to 1200 fora minute, only if night was cold or rainy

 

Really? Do you hear a loud hissing noise coming from under the hood as well?
I want you to open the hood with the engine running and check by the brake booster for any vaccum leaks, im guessing your brake pedal feels a little hard as well right?

 

yes both symptoms, but not very noticable

 

Its probably gonna get worse, find that line thats leaking and replace it, that should also give you a pretty big power increase and the idle speed should be a lot smoother.

 

thanks, i'll look for it and try to replace it myself, maybe even post DIY write up

 

Vacuum leaks are pretty common because one of the stock hoses is cheap and makes a really tight bend, right? Mine looked like it was going to break so I replaced it with some high temp silicone or something like that. It was bright orange.