Well, here is one that I just can't figure....great car, but this problem is driving me crazy (wife too ...she is afraid to drive it now). I have been swapping sensors with no results. Here is the problem...the engine will start and run great cold. When it warms up and the ECR switches to closed-loop mode, the IAC valve takes the RPMs up and down between 500 and 2500 RPMs. If the car is switched off during this time it will not start until the engine cools back to warmup operating mode. I found that a previous service job had misrouted the vac line that goes to the EGR ... it had touched the exaust tube and melted shut. The vac line is now replaced, but the surge and hot-start problem is still there. Getting diag code 123 (coolant temp sensor) during the whole time...sensor was replaced and wiring to the series ground and to the ECU was checked ok. Anyone ever seen anything like this? Tom Haywood