Expert: John Campbell - 8/14/2006

Question
1999 Mazda 626; After the car has been sitting for a while (mainly overnight) it stalls out within the first five minutes of driving.  

Answer
You might have a failing or stuck Idle Air Control valve. Another thing may be a stuck EGR valve or bad EGR solenoid. It will require you to take it to a shop and let them have it overnight so they can try to duplicate the problem as you did not mention if the Check Engine light has come on when it acts up. This will not be something you can diagnose without scanning it while it is being driven. I am assuming that the majority of your driving is cruse driving on a highway or long open roadways. This would allow a car that was hot when it got home to have an ailing Idle control or EGR to stick in the cruse/hot idle state and would not operate when going from driving back to idle or deceleration and their for the engine would stall. This is especially more likely if the car is an automatic as the engine would not be turning at the same speed as the wheels when you were approaching a stop sign or when gradually decelerating on the highway without the use of the brakes. With a manual transmission this problem is only slightly more complex to diagnose and may involve an additional coolant temp or intake air temp sensor.
Have it make a visit to the shop and see what they say on the matter once a scan tool is plugged into it.

Regards,

John