Ford Repair: 1989 Mercury Grand Marquis, mercury grand marquis, throttle position sensor

Question
QUESTION: My mgm will run run fine for a little bit and then take off with out any reason. It
surges for a really long time. Sometimes the check engine light comes on and
the engine runs ok but as soon as the light goes out the car takes off. If you
have any advice I would appreciate it.

ANSWER: From what I can gather,it sounds like you're problem is in the throttle position sensor.When you say takes off,do you mean the engine rev's up without hitting the gas.Can you explain this further for me to be able to confirm my suspicion?

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QUESTION: When I say it takes off it could do about 30+ mph without me hitting the gas. I already replaced the throttle positioning sensor and this problem persisted.

Answer
It troubles me when you say that the car is fine when the check engine light is on,and when it goes off,the car takes off.This points to the engine computer.Normally,I would have thought that you have a problem in the throttle body.Maybe in the linkage,or the idle air control valve is defective.