Friend of mine is a member on the buick forums and sent me this topic. Take a look

A Look into the GM 3.1 engine - Buick Forums

 

Good link. my daughters grand Prix has a 3.1 I'll keep this page in mind....bookmarked.

 

I've done a lot of work on the earlier 3100s ('94 and '95 specifically). I completely agree with:
1 - Leaky manifold gaskets (a headache still today, thank you nylon gaskets).
4 - EGR, the years I work mostly on have a 3 solenoid EGR and it carbons up and throws codes. For almost ALL the years since I got my '94 Grand Am (still in service), it throws code #77 about the EGR (but passes ALL emissions checks, runs fine and I've done all I know to solve it, rebuild the EGR, replace it, clean it's passage to the UIM).

The others I think are variable how common they are. Such as '94 and '95 I know do NOT have a MAF sensor, so that one is off the list for me.
Dirty injector, I've ONLY replaced two (oddly, my car, same position both times).
The ignition system, only knew one guy to have a failed ICM. I've seen about 4 coils between 3100/3400s total ever fail (one was an aftermarket replacement for a previously failed coil). As for plugs and wires, they should get changed from time to time anyways, just part of maintaining the car.
And as for intermittent electronic control failures, not sure I've ever seen that.

Like I said, some of these could be limited to specific years as to when they were "common" (GM could have had a batch of bad coil or injectors or who knows what).