I am having problems diagnosing a problem with a 99 grand am se with 2.4l on 1999 Pontiac Grand Am

When I press on the gas the rpms flutters as it idles up and back down. Also when the engine is cold is idles at around 850 rpms and idles fine in gear. When the engine gets up to temp the idle starts to lower to 650 rpms and the engine will shutter in gear quite a bit but will not stall. I have replaced fuel pump, fuel filter, fuel pressure regulator and 4 injectors with used items. I did not check the fuel pressure however. I also replaced the sparks plugs and aluminum coil housing over the coils. I cleaned the throttle body and replaced the aic valve, tps sensor, map sensor and cat but still have the same problem
I was thinking it could be the egr valve, intake mantifold gasket or oil/air separator since there is not pcv valve and notice oil residue in the air intake before the throttle body Thanks for your help Craig

Asked by for the 1999 Pontiac Grand Am
scan test for codes with a tech11 scanner so you can get data stream
I only have an Actron CP9580A with live data but what I have not had it very long need to know what to look for
the scanner should give you your fuel pressure and the sensor inputs. Does it have any codes stored?
It does not have any codes on it. I have been on live data, but I have not seen a fuel pressure reading
check for a vacuum leak and you will have to check fuel pressure with a gauge because on some vehicles 2or3 lbs can make a big difference.!!!