Mitsubishi Repair: 92 3000GT VR4 Cold runnng problem, throttle position sensor, mitsubishi dealer

Question
I have a problem with my '92 VR4 that now not even the local Mitsubishi dealer can figure out (they have had the car 2 weeks). It is a one owner, 66k mile vehicle.  The car starts fine but runs rough, misfires, idle jumps a bit, runs rich and hesitates when cold.  Once the car is completely warm (20-25 min of driving) it seems to run normal.  I have had all plugs and wires changed with OEM parts, the throttle position sensor, fuel pump, intake gaskets all replaced.  The dealership has tested every sensor that may cause this problem and found nothing wrong. They did say they pulled out the ECU and found a capacitor to be leaking slightly so they sent the ECU to be tested and it tested fine. I told them I think the leaking capacitor still could be the problem but they don't think so and won't replace just the capacitors. Do you think a leaking capacitor(s) could cause this even though the ECU itself may not be damaged...yet?

Answer
Andrew,
Even if the leaking capacitor is not causing a problem now, it will eventually.  Typically, a bad ECU is indicated by engine stumbling and performance problems after the car warms up.  But with you car having problems when cold then evening out once warm, that is a strange problem.  You may have a FIAV problem.  That's the fast idle air valve, which is attached to your throttle body.  This article can provide some good information as to what it does:
http://www.stealth316.com/2-3s-tb.htm

If the is a problem with the FIAV or throttle body, this could be the source of the problem.  See if your mechanic has inspected this.
Good luck!