Just acquired a 1991 420 SEL. Today the idle starts going in spurts (hi-low,hi-low...), all dash warning lights came on (except check engine), car stalled out- I jumped the car off & it started right back up but went dead minutes later, tried jumping it again and got nothing. Replaced the battery & it started right up & I drove it home. I would guess the alternator may be the cause, but it was replaced new (according to records) last month. Should I replace the alternator or check something entirely different. Any help would be appreciated!