My 1991 ford 150 with a 351 engine fuel injection is reving up to 25000 turns just sitting parked it goes up and down on the revs. can the problem be my egr???

If you are reving in park, it has a rpm limiter to protect the engine. If you are on the road and it will not rev, then you may have a fuel problem. Check the fuel pressure with a gauge . Could have a bad filter of pump. Depending on which type of injection system audi used.

Sounds like a lean misfire condition. Have you run a fuel pressure test? Should be 55-60 lbs. If pressure is ok during idle and reving, Ttry disconnecting MAF and see if any difference on accel.

Intercooler tube leaking

DO YOU MEAN WHEN YOU ARE ACCELERATING? Or do you mean sitting and reving the engine? If you are just reving the engine in park then the rev limiter is kicking in.

It seems that correct amount of fuel is not being supplied to the engine. Most probably the fuel nozzles have accumulated some dirt. Try spraying some carb cleaner into the air intake assembly when the engine is idling. This ought to mix with the air-fuel mixture being injected into the cylinders and if the nozzles are narrowed, should clean them up.

turn every thing on in park if voltage drops change alt

Perform fuel injector check, check the Air filter, clean MAF sensor with the MAF sensor cleaner.Dirt sometimes accumulate on the sensor and that could cause for poor mileage.Before changing your engine oil
clean fuel injectors and sludge from the engine using 3 oz pure acetone and 2 oz xylene on 10 gallons of the fuel. Drive vehicle and then change your oil. You will notice a lot of sludge coming out of the pan. After draining oil, remove pan and gasket and clean with solvents and dry with the compressed air. DO NOT clean with the rag because that can contaminate your engine and oil.

is the check engine light on.what year car and engine size,fuel injected or carb.

That sounds like the mas air flow censer or the throttle position censor to me, I had a 1991 nissan fair lady z which did the same thing when they went out. Try removing it checking the wiring plugs, and cleaning the plugs and censors with electronic cleaner (you can purchase that at a local autozone)

The check engine light could be a bad O2 sensor which would cause for the bad fuel economy. As for the reving up and down when sitting still, do you have your AC on, that would cause your engine to rev up and down as the compressor go's on and off which also indicates that you may be running low on R134. 
Auto Zone or Parts Source can scan your blazer free of charge so you know which O2 sensor you need. Hope this helps and good luck