I recently replaced a blown motor (long block) with a newer reconditioned one, I’ve worked my thru many trouble codes till I’ve finally gotten the vehicle to idle…. But it makes some concerning noises and the idle rpm increases when I removed the oil filler cap and air gets pushed out of the fill port, I want to attach a video but this forum won’t let…

 

Fairly sure that removing oil filler cap will cause massive vacuum leak. Most crankcases are running under a vacuum to control emissions. If you are getting positive pressure in the crankcase I would suspect ring blow-by or some other cause (since it is a "new" block). Hope that helps.

 

thank you for the reply, I would also like to mention that it makes the bucket ticking noise, but that might be because the new engine haven’t been driven yet and high oil pressure haven’t found its way into the valve lifterr buckets…. Any other thoughts?

 

I would expect a "new" engine to sound right at start-up. Something else is wrong and I would fix it before hurting a costly purchase. I don't have a M156 so I am not sure of its oiling system and other oil pressure controls. I know the M157 has a complex oiling system.
I am guessing here but, I would say you have an oil delivery blockage to the cylinder heads (the valve ticking) that may be causing your high oil pressure. I would be looking to ensure everything is installed correctly and all sensors and control circuits are working properly.
Also, this is a tough forum (CL) as not many people visit here. Just a rare car. Would you have better luck posting in an E or C class forum where a more mass produced car used the M156 engine. You might get a better response. Again, best of luck.

 

thank you for your insight once again! I’ll definitely post on the C section see what I can get !