my 94 940 keeps running rough and has low power most of the time. Feels like it is running lean. I have replaced the MAF, fuel pump, fuel filter, cap, rotor, plugs, wires. TPS sounds okay. My next step was to try and see how well it would run without the oxygen sensor plugged in but I cannot find where to disconnect it. Another slight hint is i have noticed sometimes the brakes loose boost. this has only happened when first starting up tho and pumping the brakes does not seem to effect the idle. Any other tips or suggestions would be appreciated.

 

Running rough and low power sounds to me that your not running on all four cylinders - but it's hard to diagnose over the internet. Low boost on the brakes sounds like a vacuum leak.

Try to diagnose these items separately. Could be many things.

Check to see if one cylinder is not firing by removing a spark plug wire one-by-one (only one at a time) when the engine is idling. Use a rubber insulated pair of pliers when doing this. As you remove a wire, the engine idle speed should drop. If you remove one and the engine does not drop speed, then you know it isn't firing.

 

"Running rough" is indeed a MISFIRE. Before you go throwing any more money at the thing, take a compression test to make sure you don't have a bigger issue like a bad head gasket or a burned valve.

 

And the O2 sensor has nothing to do with the problem. You may have a vacuum leak causing all that rough running...