I had a used engine installed to my car.i have problem with high idle and it knock and feel like misfire around 3-4K Rpm or under load. I have the Pfc reading very high knocking it doesn’t do that before i’m out of idea what is going on. I checked vacuum I dun see any leak. Plug are new i’m Out of idea.

I had some what your problem with high idle. I had this problem after changing my twins from stock to bnr’s. I changed every gasket including lim. Also removed the upper intake to remove the lim as well as to check for vacuum leaks. Started the car and ran good but idled high. So checked for vaccume leaks for weeks Including under lim. Keep in mind the car was not doing this before I changed twins and all gaskets. But after I just about gave up, I decided to loosen all idle adjustment screws on the upper intake manifold and that fixed it. I was now able to set my idle to the correct idle. How did this happen? I just don’t know, the car was running fine before how were these adjustment screws set incorrectly. Curious to see if this helps you because if you set the screws in to high of an idle it will run and bug like crazy.