I had 1987 240 for a few years now and it's been a great car. In the past few weeks it started having starting problems.. After I drive it for a while, stop and turn ignition off, it won't start again...it turns but won't start. Then, I have to just sit for 10-15 minutes and it will start again just fine. In the morning, when engine is cold, it always starts just fine. Weird thing was that it would happen once every 3-4 days, although I drive this car every day...Most recent developments was that engine turned off in the middle of the road, while driving...this happened twice in the past two-three weeks. Again, I just had to sit for 10-15 minutes and start it again and it would drive fine...I changed spark plugs 2 months ago but that did not help. Any suggestions as to what may be wrong.

thanks a lot