I had diagnostics run on my 94 5.0 bronco a couple weeks ago because it was running rough and the check engine light was on, when the results came back it was the EGR valve and because of a lack of funds i could not afford a new one. Here comes the problem, a mechanic told me i could plug the vacum line and it would run fine so i did and it ran better but still rough what do you think is the problwem and what should i do?

 

The problem is that the EGR is supposed to be there and the fact that its not is sending erratic readings to the PCM through the O2 and EVP (EGR Valve Position) sensor. (You can fool the computer by plugging the vacuum line but you can't trick this sensor if the valve isn't moving). When the PCM doesn't get the "expected" readings from any given sensor it begins to attempt to compensate for the discrepancy, hence the lousy idle. These are the two sensors I am certain are affected by this method. There may be more. Any bypass or interruption of correct signal from any given sensor will result in a change in performance... usually for the worse.

On an older vehicle plugging the vacuum line to "get around" the problem temporarily may work. It essentially takes the EGR valve out of the performance equation. However, with the intense monitoring of engine/emissions performance done by EEC equipped vehicles, the "bypass" operation isn't necessarily going to help the situation.