1998 Vortec 5.0 miss at idle (PO303)

[Jrbdjb]

My '98 Z71 5.0 developed a #3 cylinder misfire, set a PO303 code.  I found where the plug wire for that cylinder had dropped out of its holder and got on the manifold and burned.  I replaced all the wires, cleared the code and still had the miss.  As it was due anyway, i replaced the cap, rotor and plugs and felt sure the miss was cured. Nope. Checked the compression and had 150 pounds.  I noticed that at about 1500 rpm, the engine smooths out, so I connected my code reader, and after getting to road speed, I cleared the code.  Drove about 30 miles at highway speed and no codes and truck ran strong.  Pulled in to get a snack, and while idling in the parking lot the miss return and  CEL came on.  Read the code, PO303.  Headed back home, cleared the code while on the highway, no code and ran good until I pulled in the driveway.....PO303.  Any ideas?

 

Thanks! 

[wreckdiver230]

sounds like maybe a vacuum leak .

[rjm1998]

Have you figured out the problem? This is one one of the many things my 5.7 is doing.