Very Sluggish & Speedometer is out

Every now and then, the Check Engine light comes on and the car is extreamly sluggish, but will move forward and eventually get to it's top required speed, at the same time, the speedometer is not functioning either.

After a time, it sits parked, and next time I try to start it all is well, no warning light, and all functions are good to go again until next time.

Welcome to AF. As a newbie we must remind you to post the year , please. You need to have this scanned for codes to start out with.

From the sounds of it, its a 94. I had a Park Avenue that did the same thing. Just before I was going to figure out what was up with it I hit a deer so didn't bother. Got a 94 Eighty-Eight and now and then, usually low on gas it'll do the exact same thing.