I recently moved from Calif to Michigan my blazer runs fine, but after a long idle it coughs and hesitates when accelerating. Runs fine unless I sit at idle after warmed up i.e. drive thru at McDonalds, bank ect. So where do I start?

 

Possibly exhaust system, or EGR system. Mine codes the o2 sensor running lean after a long idle. Do you get any codes?

 

Sounds as though it is loading up with fuel... Have you checked for a fuel leak around the injectors (this is a TBI motor correct?)? How about a vacuum leak at the base of the throttle body? Possibly a partially clogged IAC passage/valve (I think the TBI motors had an IAC valve anyway)?

 

I'll throw 20 bucks on the timing being off a tad, Had the same problem with my 86 s10 pickup. Get a mechanic to throw a timing light on it