Cadillac Repair: lack of power, throttle position sensor, cadillac sedan deville

Question
Dear Bill,

I have an 84 Cadillac sedan deville, I live in florida, brought the car from upstate ny. In the morning when it is cooler, the car seems to run fine, after work when it is hotter seems to have less power when excelerating, and sometimes, backfires, or misses. Do I just need a tune up, or is it a fuel pump problem, or throttle position sensor. Also I was wondering if cars shipped to the northeast, or set up differently then cars sent to the hotter south, and is there something that needs to be adjusted. When you get the car up to 60+ on the highway, is when it really seems to run rough, skipping and seems to have little power to go over 65+ the speed limit here in fla. No matter how much you press on the gas pedal, just seems to fight to get going.. Thanks in advance for all your help..  

Answer
Hi Bruce, You might benefit from a tune-up but first test the fuel pressure at idle and if you have a long enough hose on your tester while going down the road. You might find that the pressure or volume of fuel is starting to starve the engine and replaceing the fuel filter first and then the pump will return the performance. If pressure is about 12-13psi, the 9psi low spec means the pump is starting to go bad, then other things need to be looked at such as coolant and manifold temp. sensors, tps, oxygen sensor, map sensor etc. to see if they are in a normal range. That might be best done at a shop and then you can determine if you want them to complete the repair or replace the part yourself. Driveing from a cool to hot climate shouldn't affect your car if everything is working correctly. I would put my money on the fuel pump and filter.  Hope that helps. Bill