problem running after alt/fan belt broke

[boston bimmer]

so I was driving yesterday and my alt/fan belt broke in my m42 so I got a new belt and put it on but now it will not run right. It will idle a little rough but not too bad but when driven it lags badly up to 2500rpm then accelerates like normal. When it goes back to idle it stalls. The check engine light goes on and off intermittently and if held steady at any rpm it will run rough. My initial thought is that the alternator is bad  on a side note I just put in an electric fan and was also wondering how to disengage the clutch fan (snip a wire somewhere or something) or if that could be a problem too (the new fan was installed after the belt broke I was wondering if it might be the fan clutch having issues) please let me know what you think thanks!

[RidingSimple]

check your vacuum hoses and AFM.  Might have been shimmied when replacing the belt? (I know it sounds random but it's worth a check).

[HATER-PROOF]

I may not be the brightest star in orion's belt, but to me, from your description-something is pulling the team down.  (1) start the engine and take a look at your belt, If it look's like it's getting ready to pop-off, tighten up your alternator bracket.  (2) If you're running a new "SPAL" then your going to need to look at the possibilty of running an upgraded alternator, but my question to you what type of fuel do you put in your tank? Think about--rough at low Idle, then smooth after acceleration?--fuel filter clogged.  It's just my quess dude-I hope you get it fixed.

[boston bimmer]

thanks for the answers it ended up being the mass air sensor went bad and a byproduct of the whole ordeal was that I found out my alternator was bad as well. I was able to pick up a whole new intake, alternator and side trim from my local guy at sports and imports and everything is running great now