You might also want to check out how clean/dirty your MAF is. I had the same issue (among other driveability concerns) with my Bravada and it was entirely caused by a dirty MAF (mass air flow) sensor. On the bravada, it is an open element MAF, but in the Bonneville, you can't really easily get to the elements to clean them. The easiest thing to do is get some Throttlebody/Carb cleaner (O2 & CAT safe) and spray the living crap out of them until they look nice and clean. If you think that you can get a q-tip up around the elements, then that would clean off any stubborn debris, but be very careful. Those elements are very fragiile and easy to break. And the MAF is $$$!