Rough Starts and Bad Smells

I have a 92' Cherokee w/ 4.0 and a AX-15 5 speed with somewhere in the neiborhood of 170K on the odo that's started to give me problems as of late. First off it starts really rough after it's been sitting a while (more the about 12 hrs.) and when it does start it sounds like it's only hitting on 5 for 30 seconds or so but then it smooths out and runs great. The other thing is a very gassy smell coming out the tail pipe...like it's running REALLY rich. I haven't noticed a huge drop in fuel ecconomy though. The #4 plug is ashed and I'm thinking the smell from the back is most likely coming down from that one. So that's got me thinking a bad fuel injector, but I was also wondering what, if any, of the emmisions control sensors might be causing it. Any help or experences would be greatly apperciated.
Patrick

My guess would be an injector that is dribbling after it is off. The fuel rail remains pressurized after you shut down, so it can dump quite a lot of fuel over a long period.

There is equipment to test for that. You would need a pressure gauge that hooks to the fuel ral, and an injector tester that fires the injectors one at a time. It would probably be cheaper to go to some shop that has the stuff already, though it's more fun to own it

An untested test idea: You might be able to test the theory by parking it, and then immediately releasing the fuel pressure in the rail (watch for flammable spillage) through the valve. If it starts less roughly than usual the next day, it's likely a leaking injector.