egr madness--please help

I have an annoying problem with a 1993 4.6L engine. While passing on the highway, one day the "check engine" light came on for about 30 seconds, then went out. This had never happened before. Then whenever I was on the highway, especially going uphill, the light would again come on, then go out. I checked the codes and got a 332 for 'egr valve opening not detected'. I had just replaced the valve two months earlier, so that was weird. then the light would come on when the engine was warm, but STAY ON until the key was shut off. I checked the codes again and found the 332 code again, plus a 337 which is 'egr pressure transducer/ switch voltage too high'. I replaced both the pressure transducer and the egr switch with no luck. Then someone told me to clean the throttle body, which I did, meticulously. It made the car run a little better but still the annoying light. I even took off the egr valve again, to make sure that the diaphragm had not ruptured somehow, but the valve works fine. It holds vaccuum and the valve passage itself is not dirty or obstructed in any way.

The car now displays this error message every time I drive it, but the car runs fine. I checked the voltage of: maf sensor, coolant temperature sensor, tps sensor, iat sensor, etc. but could not find any problem with them. The error message used to come when the engine was warmed up, but now it comes on sooner.

Any help at all from anyone would be most appreciated. I am at the end of my rope, and I hate bringing my car to the garage because of the money they charge unless it is something I can't handle, and this doesn't seem like it is, so as a last resort I will.

Thank you in advance for any help

mrtorsionbar@hotmail.com or reply here, thanks! 

hmm I can't remember but I think that particular model has a DPFE sensor on it.  If this is the case your problem is going to be either of two problems.  There are two hoses coming from the dpfe sensor. An upstream hose and a downstream hose.  They both run to the egr pipe at the back of the engine.  There are two small hoses coming from the pipe.  Check these hoses and make sure they are not stopped up.  Also check the sensor to make sure it is not bad.  Those sensors are bad about getting water in them and shorting out but generaly when that happens it shuts the computer down and sometimes fries the ECU.  Now your car may not have an dpfe sensor so make sure.