93 taurus 3.0

i got a 93 taurus, v-6 with trouble codes that were scanned at auto zone.. the codes are 25, knock sensor 34 EVP(EGR Valve position)voltage out of range
51 ECT (Engine Coolant Temperature) sensor signal voltage too high
the check engine light would come on an go off all the time....... start car and drive off and about a block away and it would come on.. then go off and back on and then stay on.... i learned that the Taruus GL that i have does not have a Knock sensor so i ruled out the code 25 as being the culprit... i then checked looked at the ECT and did not knwo how to check it so i went to the EVP and did not know how to check it.. i then went to the air filter and it looked brand new.. remembered that i changed it about one month ago... i then removed the MAF sensor and cleaned the two little wires/sensors in there with some windex on Q-tips and scratched up the electical connection on it to make sure it was making good contact to the harness... put it back in and drove around and the car seemed to run alot better. before it was killing when starting up and seems to have a shake in the engine like when you have a car thats flooding with the old carbs. so far two days now and the check engine light did not return.... could this be the fix for this car??? three other codes and noting mentioned about the MAF, but cleaning it corrected the problem... or did it????? thenks for a reply... well i found out that the ck eng. light came back on.. i checked the ECT by putting the ohm meter on it when the engine was cold and then when warm and it seemed to be OK... nothing when cold and movement on the needle when hot.... then took out the EVP and brought it to auto zone and they put pressure on the valve and cheed it with the meter after putting six volts on it and they told me it was OK... i later returned home and pulled off the EGR and blew into one side and it was closed(no air flow from 1/2 pipe hole)... i then put vacuum on the egr and the valve was now open.. it seemed to be OK... i checked the small hose on the EVP and it seemed to be alright, no blocked.. the passage that the EVP small tube that went to the exhaut manifold seemed to not be blocked.. the tubing from the EGR seemed to be clear also... any suggestions????? one more question: when is the vacuum line to the EGR valve suppose to have vacuum to it???? i think the vacuum is whats suppose to open the EGR valve.. if i remmber correctly the intake manifold should be high in vacuum when at idle, then go off when you give it gas, and then come back on when the car is coasting along??? at least that is the way it was back in the old days of the vacuum operated windshield wipers... any suggestions???? thanks for a reply.....

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