Hi all,

I own a 1999 Mecury Mystique, 2.5L V6, 24 Valve DOHC. So far it's been a great car and I've enjoyed the experience!

Recently it broke down with several issues that we're in the process of fixing / figuring out. One particular issue that I'd appreciate some guidance on is this: We've found a significant amount of raw, liquid fuel inside the intake manifold




We noticed this while taking it off, because liquid fuel drained out the pipe in the top right of the picture there. We also noticed fuel in some vacuum lines





Potentially relating to this problem, the exhaust O2 sensor needs to be replaced - And upon doing so, we found what we'd call a heavy/excessive amount of carbon build up on the sensor. It's probably hard to see in the picture - But when we first pulled it out, it had a relatively thick coating. Some has already been wiped off in this picture






We have a home OBDII reader, and here are the codes we got off the engine if it may help diagnose anything
Error Codes
P0155 - O2 Sensor Heater Circuit
P0156 - O2 Sensor Circuit
P0401 - Exhaust Gas Recirculation Flow Insufficient Detected
P1520
P0171 - System Too Lean
P0302 - Cylinder 2 Misfire Detected
P0301 - Cylinder 1 Misfire Detected
P0161 - O2 Sensor Heater Circuit
P0174 - System Too Lean
P0303 - Cylinder 3 Misfire Detected

Any advice on what may be causing this fuel problem or anything you see would be of much appreciation - Thanks in advance!