"1998 chevy s10 2.2 4cyl. cranks and will idle but very rough want do anything when i accellirate thats the new problem old existing problem is #3 and 4 injectors not working scan tool said injection curcit board is grounded
not letting them work..."

SOURCE: 1987 chevy S10 engine idle problem

relace the throtle air idle valve.The temp switch will allso cause this problem.

SOURCE: Chevy 3500 Express truck. fuel problem?

IF YOU GOT CYLINDER MISFIRE.OR OPEN FUEL INJECTOR.THAT WILL CAUSE THE PCM TO ENRICHEN FUEL MIXTURE.TO ADJUST TO DEAD CYLINDER.WHICH ACT AS A LARGE VACUUM LEAK.THATS WHY YOUR EXHAUST TAIL PIPES HAS A RAW FUEL SMELL AND WHITE SMOKES.

SOURCE: 1998 chevy blazer 4.3 v6 4x4 fuel injector problem?

It could also be your alternator.

SOURCE: 97 chevy pu 305 vortec, had cyl 6 misfire and

thats usually a sign of a vacuum leak, recheck and make sure you don't have any loose hoses, or cut intake seals

SOURCE: 2002 chevy trailblazer has rough idle

There are numerous things that can caise a vehicle to idle rough. Could be a throttle posistioning sensor. pcv valve, dirty fuel filter, worn spark plugs and wires, possible O2 sensor. If the vehicle has not had a tune up yet, I would recomend one. Even if it doesn't fix your issue, the vehicle is ten years old and probably needs on anyways. Start there, then rule out the cheaper stuff next. pcv valve and fuel filter, inexpensive and it's probably time anyways. If you are getting an engine code, stop in to advance auto. They'll plug it in for free. If your still having problems, you may have to break down and tajke it to a mechanic to get plugged into a real diagnostics machine.(probably run you around $100)