Truck Repair: 94 Dodge Ram 1500 3.9L V6, dodge ram 1500, vacuum leaks

Question
Van,
I have the above truck with 85,000 miles and runs good at highway speeds but idles poorly, especially when engine is hot and engine bogs down occasionally when accelerating, especially with quick accel.  About a year ago, the Cat. Converter went bad and took it out of the system.  No problem until recently.  Engine code (#21) says problem with Oxygen sensor circuit.  I had the sensor replaced but still had the same problem and same code keeps coming up.  Replaced the idle air control valve...same thing.  Can find no obvious vacuum leak but I have no way of testing myself.  Wiring (plugs etc) seems OK.  I have tightened all bolts around throttle body and cleaned throttle body with spray.  Had one local mechanic check it out and he says his computer said "dirty connections" (where, I'm not sure), but he says he cleaned them.  Don't know that he checked for vacuum leaks but he felt like it was not the problem.  Problem still persists and still get same fault code (21).  Any ideas?

Thanks for any help.
Jerry

Answer
Hello Jerry,
There are two places that can cause vacuum leaks that most people overlook.
One is the power brake booster, and the other is the EGR valve.
Bad plug wires could cause a rich condition, which would cause the oxygen sensor to set a code, but the egr valve leaking would cause a lean condition, which also would cause the oxygen sensor to set a code.
If the cat converter went bad, I would suspect rich, since that will cause a meltdown in the converter from all the unburned fuel.
Van