Yesterday, I was doing about 70-75 MPH for 50 miles when my Turbo engine starting "coughing" and began losing power. I happened to be near an exit at a slight incline and I took it. This put additional load on the engine so I pulled it over while noticing in my side mirror black smoke coming out of the exhaust. While checking wires and vacuum lines under the hood, I listened to the idle go up and down (800 RPM to about 1500, I think). After a minute of this it settled down to a nice steady idle, right where it belonged, and with no black smoke out of the exhaust. I let it continue to idle for another 5 minutes with no more problems. (I found no wires or vacuum lines disconnected--the car just 'corrected' itself).

I eased it back home on the side roads with no additional problems- smooth acceleration and decent power, almost as if nothing had really happened. And I've been driving it around town all day, with no additional hiccups.

Yet I know the car is telling me something. I just don't know what exactly.

My guess at the moment is a failing Fuel Pressure Relay (though there is no gas in the vacuum line); or perhaps the Coolant Tempature sensor. Any other possiblities about what made this run momentarily rich at speed?

Thanks for reading thru this long post!