What your looking for is Compression in ALL 4 Cylinders that are ALL close to each other.
Every Engine could very, but 120 would be good, 170 better. If ANY Cyl. is different by 20%
of the others, there are issues.
Other things to look at would be Fuel Pressure, Throttle Body, and I know you
said it isn't an Ign. Problem, but a GOOD TUNE-UP may STILL be in order, and
provided you have a Reputable Shop do it, they will all so check the other possibilities.