What is causing the misfiring under load at higher RPMs?

TOYOTA PICKUP
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CROWNZ88
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My truck is miss-firing at about 4500 to 5000 RPMs. It usually does it when I go into passing gear. Most of the miss-fires are in 2 but also in 5,6,8. I have changed the mass air flow sensor, O2 sensors in bank one, spark plugs and wires, and cleaned the throttle body but I am still having the same problem. The truck runs great at normal driving with no miss fires. I am also having trouble trying to perk the coolant system. I recently replaced the coolant flange on the right side of the motor because it was cracked and leaking. After I replaced the part and put everything back together, I attempted to perk the coolant system. I put the heat on high and filled the reservoir and waited for the thermostat to kick on. I sat in the car and after about 5 minutes I could feel the hot air coming out of the vents, but moments after that cold air began flowing and the car would just continue to overheat.
Apr 15, 2007 at 2:05 AM
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RASMATAZ
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[quote:b2d0ea90a9="crownz88"]i have a 1990 toyota pickup truck, it just recently started making a loud scraping sound when i press on the gas. the sound isn't continuous, it's just briefly when first start to accelerate. if it gets any worse i'll take it to a shop. i dont know much about cars, so any ideas on what might wrong with it would be great.[/quote:b2d0ea90a9]

Moving or while park?
Apr 15, 2007 at 7:12 AM
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CROWNZ88
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I sat in the car and after about 5 minutes I could feel the hot air coming out of the vents
Apr 15, 2007 at 1:45 PM
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RASMATAZ
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[quote:659dbe621f="crownz88"]seems to be fine in park, only while moving[/quote:659dbe621f]

Could be the front brake pads need replacing-is it more like a grinding noise when you start moving or the fan touching the fan shroud
Apr 15, 2007 at 5:28 PM