1966 Coupe 302 with Holley 4bbl and Edelbrock Performer RPM intake points distributor C4 auto transmission As the title states, my car is idling rough when I put it in gear (Reverse, Drive, 1, 2), but idles fine in Park and Neutral. It starts up immediately every time, and it drove fine, but would struggle when stopping at a stop sign/light, or even slowing down for a sharp turn - basically any time it idled in gear. A little History: Car ran great until the Mallory electronics started crapping out. Car would die on the road and then wouldn't start until it cooled off. I replaced the distributor (Mallory electronic w/out vacuum advance) with a points distributor from O'Reilly's. Went ahead and replaced the coil at the same time. Ran fine for a while after that. Checked Timing and Idle: I put a timing light on it, and I noticed that after the engine warmed up, my timing light stopped working. Did a little testing, and I was getting a light when I put the inductive pickup on the coil wire or spark plug wires other than #1. I replaced all of the plug wires (and the big coil wire) and the distributor cap. Now the timing light works on #1 until I put the car in Drive - then I get no light unless I bump up the idle high enough so that it stops stumbling. Here's something weird... with the trans in Drive (brakes applied firmly), the idle is rough until I get the curb idle adjustment screw to just the right spot, then the RPMs jump up and the car idles smoothly. Timing light then starts working (on #1). Turn the screw counter-clockwise 1/8 of a turn or less, and the RPMs drop significantly and the car starts to stumble. Turn it back clockwise 1/8 of a turn or less, and it smooths out, but the RPMs in Park/Neutral are much higher. Checked for Vacuum Leaks: I bought a vacuum gauge and used that to set the timing. I was pulling a max of 21-22" of vacuum from the big port on the back of the carb, so I dialed it back to 20" and tightened down the distributor. I think I ended up with initial timing at around 7* BTDC. The carb's vacuum advance port has 0" of vacuum at idle, but jumps up when I rev it - that checks out. I did lots of checks for vacuum leaks - pulled all of the different lines (brake booster, transmission vacuum modulator, etc.), plugged them, and tested - problem persists. I squirted WD-40 all around the vacuum lines, base of the carb, around the intake manifold gasket, and in the carb throats. I didn't detect any vacuum leaks. Tested Power Valve: With the car idling in Park, I turned the idle mixture screws all the way in and the car would just about die - had to back them out quickly to keep it from dying. I'm pretty sure my power valve is working. I have performed most of my tests with the idle mixture screws at 1 1/2 turns out from closed. After all of this, I set the idle in Drive high enough so that it stopped stumbling and took it for a test drive. Now it stumbles under medium acceleration. Not sure where to go from here. Could it be a bad coil? Points/condensor? Carb? Fuel delivery problem? Thanks!