[MT-2500]

Originally Posted by Ltl_red

My 96 Blazer has been idling a little rough on and off for the past couple of weeks. I thought it was just bad gas or the fuel filter. I put some 104+ in my tank for the gas and replaced the fuel filter (seemed to run better after that).

BUT.... My problem now is that my truck is stalling and the tach is freaking out. This morning I pulled out of the garage and it stalled in the drive way. Started and it stalled again in the road. Started again the tach shot to 2K then droped, I got to the stop sign and it stalled one more time. I was thinking I was going to have to turn around and get my other truck, but it stayed steady after that... I get almost to where I am going and I am approaching a red light, I notice that my tach is jumping all over the place from 0 (almost stalling) to just about 3K (damn), I pull up to the red light and the tach continues to go nuts, I keep it running by giving it a little gas at 0 so it does not stall out.

Anyone have any ideas as to what this could be caused by, or what may fix it?

I would get a engine capable scanner on it and check out rpm readings in scanner.
post back any codes.
Any check engine lights ?