Engine Performance problem
2000 Chevy Malibu 6 cyl Front Wheel Drive Automatic 120000 miles
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Occasionally (1 in 5 times) when trying to start my wife's Malibu, it turns over, starts running momentarily then revs up to about 2000 rpm, then drops down and dies - all in one smooth motion.

Also, when accelerating, the engine seems to not be able to keep a consistent rpm. It will go up and down approximately 500. If you step on it, it accelerates fine; but lightly accelerating will always cause it to "pulsate" like this.

You guys seem like you know a lot, I'll appreciate any input I can get. I'm at a loss here and don't want to start in a downward spiral of replacing parts to find out its something simple like a fuse or something. Thanks 2carpro guys.