1999 Passat bogs under load and seems to be misfiring. Could it be the fuel filter or the ignition sensor and how do you test/replace?

Defective ignition coil, defective spark plug, defective fuel injector, defective fuel injector driver circuit, low engine compression on cylinder #5, defective PCM (very rare)

Check coolant level,thermostat,

Raw fuel from the tail pipe I would think maybe a bad TPS, fuel pressure regulator or injector. More than likely a bad regulator or throttle position sensor. Check your fuel pressure after the regulator at idle and wide open throttle. At an idle the pressure should be 20-30 psi lower than at wide open throttle. If your getting to much fuel pressure it can cause it to bog down and lose power due to extremely rich conditions.Will also have strong exhaust fumes.

replace fuel filter or fuel pump

How about a defective fuel pressure regulator, buy a fuel pressure test gauage from Autozone and test the fuel pressure under a load and at idle..

35 is low fuel pressure, should be around 40-44 PSI and 46-50 PSI under a load, replace the fuel filter it may be clogged.

You have low fuel pressure, check fuel filter and fuel pump.

check the fuel filter and the EGR valve

I Would Suggest That You Complete A Engine Cylinder Leak Down Test.....(not A Compression Test But A Leak Down Test) this will tell you if you have internal problems....possible worn rings or a burnt valve(s) I would use a smoke machine to check for vacuum leaks also. Good Luck

YOU MAY HAVE CATALYTIC CONVERTERS GONING BAD HAVE THEM TESTED