Hi I have a 1991 3.1 V6 and am needing some help finding out what's wrong with it . Here is a list of all parts replaced so far, I may have missed a couple so if you have any questions please feel free to ask. The only thing I haven't replaced is the harmonic balancer . Oh the timing chain & gears and water pump were replaced just before I bought it . When first started it runs smooth but as it begins to warm up it starts running a little rough and once you take it down the road the oil pressure makes it's way from 80 down to the last white line before the red but it starts missing and surging before that point . It stalls when your stopped at a light or stop sign but will start right back up. It threw a code for rich fuel or o2 sensor the last time I took it out but as you can see in my list of parts the o2 sensor is new , the longest distance I'm ably to take it before it acts up is about 6 - 12 miles from the house .

IDLE AIR CONTROL VALVE
THROTTLE POSITION SENSOR
FUEL PUMP
FUEL PUMP STRAINER
FUEL PUMP RELAY
FUEL FILTER
IGNITION COIL
OIL PRESSURE SWITCH
DISTRIBUTOR
DISTRIBUTOR CAP & BUTTON
IGNITION CONTROL MODULE
EGR VALVE
MUFFLER
AIR FILTER
AIR CHARGE TEMP SENSOR
ECM COMPUTER
FUEL INJECTORS
CATALITIC CONVERTER
O2 SENSOR
MAP SENSOR
PLUGS AND WIRES
SURPITINE BELT

 

datalogging probably would have sped up this process and saved you a bunch of money... my money is on the coolant temperature sensor. oil pressure is dropping because it is running a much lower rpm? make sure no fuel in the oil once problem is corrected.

 

I was looking over my receipts and the coolent temp sensor was replaced also , I checked and there's no fuel in the oil . I took it out a few days ago and of course it acted up like always be it threw a code for a rich fuel or o2 sensor and the o2 sensor was replaced already . I'm so fed up with this car I'm about ready to find a cliff and shove it off it I've got $8000 in it so I guess I can't do that :/

 

Disable the egr valve, the egr valve regulator might be letting vacuum to it at idle, which it shouldn't.