94 blazer 4.3 vortec 95percent of starts I have to give it gas to start the rogh idle til warm and even when warm its slightly rough. There's gas smell and black suit coming out of exhaust. When I'm driving it like pulsates . I replaced plugs wires cap rotor the coil. . I replaced the pcv valves. Oil change. Air filter is good and I can't find vacuum leaks. I'm gettin horrible gas mileage. It has 210000 miles. Any help I'd appreciate it. It looks like o2 senser was changed before but not sure

 

Im going to assume you have the cpi engine (vin code W) get a fuel pressure test done if it drops off quickly when the fuel pump shuts off id be willing to bet the fuel pressure regulator or spider injector unit is leaking easy repair but very common issue also pull your oil dipstick and see if the oil smells like gas.
You may also want to look into pulling the EGR and cleaning it really well and putting a screened gasket in upon reassembly. Let us know what you find and we can help further.

 

Just seconding Outsydr's suggestions.

If you want, you also can pull the Vortec cover from the top of the engine (2 T-30 bolts), pull the IMTV below it (2 T-25 bolts - could be T-20) and look into the intake plenum. Washed spots can be seen from there - mine were easy. If you pull the IMTV, spray a little WD40 around it, then gently twist it side to side until it loosens and you can pull it. Before you reinstall, lightly lube the O-ring with engine oil.

If you see washed/clean areas on the passenger side, it's your fuel pressure regulator. If on the driver's side, it's more than likely the nut kit (fuel pressure and return lines). But I'd be willing to bet it's the FPR. You can get a replacement from AutoZone/O'Reilly's for about $45 and it comes with the Torx Security bit needed to do the swap. You'll also need the upper plenum gasket, about $15. Get the screened EGR gasket while you're at it, too (it keeps carbon chunks from sticking the EGR open in the future).

After you replace the FPR, if that is the issue, pull the EGR and clean it, paying special attention to where the pintle seats against the base. Then clean the passages in the lower plenum. Reinstall it with the screened gasket.

 

Just a stupid question-any service engine soon lite on? Just a stupid question. Jerry

 

I'd bet on the EGR valve, My 94 blazer ran real rough, pulled off the EGR valve and cleaned off all the carbon and it helped out. I pull my EGR valve and clean it every 6 months. I replaced the EGR valve once and it work for a year then went bad again. So I just keep cleaning the one I have. it seems to help