Hey Scotty,big fan you took me through my first steps of fixing cars! Super happy to found your channel! One big issue for my side: Peugeot 406 Coupe 2002,2.0 16v 136 bhp. Changed plugs,iginition coil,MAP sensor,Idle control valve,TPS almost everything,checked for vacumme leaks and cleaned the intake,new egr and so on. The car has LPG but it doesn't make a difference if drive on petrol or LPG problem is still there:

Random Hard starts,when the car idles, it stalls and misfires badly. When you hit the gas it accelerates superbly. I get codes P0403 Exhaust Gas Recirculation Circuit Malfunction, P0300 (Random Misfire) and P0170 Fuel Trim Malfunction (Bank 1). I went through all your videos maybe 10 times,nothing helps. Peugeot people say hyd.lifters need to be changed. Besides this car has superb compression 12/12.4/12/12.4. Any thought?

Don't touch internals like hyd lifters - your problem is likely related to the LPG retro modification - if you want to check it then disconnect the LPG system completely and see how she runs without it - if it does run well then you"ll know its there is something wrong with the LPG system.

I already tried that . No difference. Really running out of ideas. Thanks for your quick response!

well, if egr is stuck open it will do that, remove the egr and put a metal plate there and see what happens first. Pray it's that eay

Already did that , no difference. EGR is electronic I also replaced /cleaned the openings. BTw Catalytic converter has been replaced with a resonant tube. Also on the o2 sensors before and after the pipe have specially designed valves to allow very little amount of exaust gas to enter giving a near perfect reading(0-6) when you press the gas. When the car is idling LTFT is moving a lot 0-30. I believe all problems are comming from the P300(random misfire) code. The reality is I have idea where this is coming from since I observe good performance, good fuel econ.
Is it possible the cat is creating the misfire?!