Ok, did some more tests, found the problem. Compression was good, 175 psi on cylinder 4. Problem goes away when I cap the vacuum line going to the brake booster. However, the brake booster is brand new (from Vick Autosport). I replaced it because the old one was leaking and full of fluid. I pulled out the check valve to make sure it was indeed checking, and it is. For now I have capped the booster on both sides, but any ideas for a long term fix?
Edit, I unbolted the master cylinder from the booster, the large port of the booster seems to leak some vacuum (I can feel it pulsing with the misfiring engine), maybe my booster is DOA?
Last edited by Zuofu; 08-13-2017 at 02:16 PM.