1998 f 150 4x4 4.6 motor won't run over 40 mph. No check engine light.Check TPS checks ok.When you back off gas then push gas runs good up to 40 mph and will not run over 40 mph.
check the operation of the EGR valve...is supposed to introduce exhaust gas into the combustion chamber if the ignition is too hot...perhaps this system should be checked for proper operation...your smog guy should be able to fix it~
I wouldn't be at all surprised if your Catalytic Converter is plugged. A simple check - unbolt the exhaust somewhere before the cat and take it for a (noisy) ride.
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