Mitsubishi Repair: engine idle, vacuum leaks, butterfly valve

Question
I have a 1992 Laser AWD Turbo 5 speed.  Once the car has been warmed up and
driven about 5 miles the engine idles up and down.  If you turn off the car and
then start it up again it idles okay until you drive it about 5 miles or so.  
According to the mechanic it is not the IAC, and I changed the ECU but it is not
that.  You have any idea?

Answer
Mike,
If it's not the IAC, the rest of the intake system should be checked.  Vacuum leaks in any of the hoses for the intake or turbo can cause idle surges.  Dirty EGR valve, sticky throttle butterfly valve, or blocked Fast Idle Air Valve can cause your problem as well.  You should be sure to have your mechanic check your ignition system.  Check that each spark plug is firing properly and that the engine is timed accurately.
Good luck!