What causes the engine to lag between 20 - 40 mph?
Just bought it. It has 149,000 miles, 98, 5.4L engine. It will get up to speed over time. No maintenance records, or owner's manual.
Lots of different things could cause this. Is check engine light on? If so what are the codes? Since you just got it and don't know how its been taken care of I would start with a good tune up( plugs, plug wires/boots, air filter, fuel filter, ect.). Doing this should help it out. Also a stopped up cat converter could do this. Look at it and see if its glowing red.
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