So I got my 302 all done broken in and running ok... here is the back ground. 302 over .030 I opened up the exhaust ports on the heads. I put on the intake from an 83 mustng gt facotry aluminum 4 barrel. used comp xe-262 cam with matching springs etc.... and to top it off a rebuilt edelbrock 1406. the confusion is when it is idleing it consitently bounces between 500 - 800 rpm. other than that runs and drives excelent. I have checked all the lines for vacuum leaks and the carb base for leaks and nada makes no difference. could it be the metering needles pulling open to early or something I have either the orange or yellow springs in it from the edelbrock calibration kit.. I have never had a carb do this.
The early 80's GT 4 bbl intakes have an EGR port under the carb, are you sure that's not the source of a vacuum leak ? It could be completely covered by the carb, thus killing anychance of detecting a leak from the outside, but at the same time allowing exhaust gasses to screw with the idle.
I have a spacer / heat shield plate that completely blocks off the egr hole and I checked it by spraying gase right at the area ... I keep a bottle of gas mix in a windex spray bottle for farting around with my old skidoos in the winter.... I tried that every where an there was no leak. the vacuum christmas tree has no leaks I tried all sources of possible vacuum leaks. I am stumped.
