i have a 91 rs / 305 cid .
motor runs great when cool but misses and pops back through throttle body at lower rpms. when its up to operating temperature . most all electrical components are new . timing is right on . also has new computer . car ran good for about a month and just started this stuff
anybody got any ideas ?

 

cam no good

 

1.too lean (first paragraph)
2.too advanced (first paragraph)
3. jamming advance (first paragraph)
4.wiped cam (second paragraph)
5.fouled plugs (third paragraph)
6. you popped a plug wire off, put em back on
7. you didnt tell me enough to tell you which you did

too lean or too advanced, or possibly advancing but the rusty mech advance is jamming up before it falls back to low rpm, if it's comp controlled distributor get a real one, then replace the module the coils, and the computer, and the pickup.... basically get a mech distributor if you have comp controlled...

if you wiped the cam, which happens, but it's easy to tell, pull the valve covers and start it up, make sure that the valvetrain is working correctly, if valves arent opening as far as the others, you wiped some, pul the cam and lifters, replace em, if you bent a pushrods replace em, and put new plugs in.

check the plugs and cross em to a plug chart, if they black, you fouled em, too rich computer and new plugs, if white you're lean

honestly backfire through the carb or tbi... is lean or too advanced. cam is a major mechanical defect, and since it ran fine it would have to be you wiped it, which happens, but, check your timing, make sure you check it at the right point for your advance curve... and if you dont know your advance curve, buy an advance kit and figure it out, and if you're lean, you need an air fuel ratio meter or someone who has one, and then you have to reprogram your computer?!? this is where the injection dude boards would be better

 

I would get rid of the computer controlled carb and dist and put a good holley carb,dual plane intake, and mild cam. The wiring is not that bad to get rid of, as long as you keep the essential wires (coolant, oil, tach) together for the gauges. Many people have done it over the weekend and can tell you exactly what to do. Check out www.thirdgen.org and do a search for the topic.