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If you have not changed over the distributer cap and rotor recently you will want to remove the cap and check its condition. Some of the distributers in these engines are suseptable to moisture and will turn the contacts inside the cap a blue/green color. If you find corrosion in the cap replace the cap and rotor, check the plugs and replace if worn.
If you have recently done a tune up or the cap and rotor look ok, look into the coolant temp sensor and the intake air temp sensor. Check the coolant level and be sure it is full, low coolant will give a false reading to the coolant sensor.