This 84 bluepra I picked up at auction Saturday has slight sputtering or spitting eminating from the exhaust. Engine idles very smooth until it warms up, then the spitting starts. Can definately feel the spitting holding hand over the tailpipe. Engine RPMs remain constant throughout despite spitting. Have not done compression test yet, but vacuum gauge shows a rock steady 21 in. Acceleration is smooth and strong in fact, seems to run great at any speed but idle. Starts on first crank every time, revs high, then settles back just like its supposed to. Spark plugs look OK and appear to be fairly recent bosch platinum tips. Have not yet checked resistance on plug wires but they don't seem brittle at all (says sumitomo on wires, not sure if they are original). Already swapped a new dist cap due to much corrosion on the tabs inside. Listened to each injector with stethoscope, they seem to be clicking in perfect rythm. EGR valve operates buts does not cause stumble so I suspect thats plugged so a leaky egr doesn't seem to be the problem either. Have checked all plastic and rubber intake plumbing and vacuum hoses thoroughly for vacuum leaks and don't appear to be any. Appears to have original cat - could that be partially plugged and cause this symptom? What else to check in what order?