Greylock

I just purchased a '93 300e. It starts fine but won't keep running unless I rev the engine for a short time. Once on the road she drives like a dream. The gentleman I purchased her from indicated he had replaced both the wiring harness and the MAS. The OVP appears to be fine (the fuse at the top is ok).
I need suggestions as to what else it could be. Please help as I am new at this.