Sometime back I posted a problem with warm starts with my 240. It would start fine when cold but when restarting when warm, it would barely run. Slowly over time it also began to give some difficulty when cold. I replaced the RPM sensor to no avail. I tried a working fuel pump relay and a working AMM. Again no better. I finally needed the car to run, so I brought it to the dealer. Turns out it was my O2 sensor - the heater on the sensor was shorting out causing the voltage readings to be all over the place. If I disconnected the heater wires, it seemed to work OK. Of course I should have checked this but it was only 4 months old (the one for the Ford Mustang). This time I bought a direct fit from Autozone. It took 20 minutes to install. It now runs better than ever.

2 morals for this story. Check the normal stuff first, but find a good trustworthy shop for things you can't do for either lack of time or expertise.