Engine Performance problem
2000 Mercury Sable 6 cyl Front Wheel Drive Automatic 75000 miles
I have gone through the Tune-up, and coil pack replacement, and 1 vacuum hose replacement, and my Check Engine Light comes on still. The engine will miss for a little, and the Light flickers, then goes on solid. I drive it a couple of days and it goes off for a few weeks, then does the same thing again.
When they did the tune-up, did they replace the Spark Plug wires? Often this is overlooked, and led to my replacing dang near everything before it finally fixed a similar problem to yours.
Also if they used cheap non-platinum spark plugs incorrectly gapped (0.53 is correct) then you will have engine trouble codes. Checking the easiest plug to access, the one on the front far left (as you face the engine) is the easiest to see what you have. Non-platinum plugs will cause the engine to foul in the worst way, as I have recently found out.