After driving in traffic on a hot day it runs rough and PO302 code comes up. on 1996 Ford Ranger

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Runs fine, let it sit for 20min then start & it runs rough & PO302 pops up. Turn it off let cool down for awhile & then its fine. Replaced coil, plugs & wires and fuel filter. No overheating, temp gauge is good. Could it a intake manifold gasket leak or bad fuel injector? Only happens after driving in traffic on hot day, runs fine, shut it off for 20min then start up & rough idle & PO302 code.
(2) Answers
(2) Comments
Try some injector cleaner with Chevron Techron. If that dont help after driving awhile, a week or so, have the injectors professionally cleaned.
Possible vacuum leak but not as likely as an injector problem. Since you have installed premium ignition parts, i'm sure (?)
I belive that solved the trick. I added a bottle of Zmax to the oil (suppose to clean the internals of the motor) , then added a bottle of Lucas fuel injector to the tank and filled up with 91 octane at Shell, once i got down to half a tank i refilled with 91 octane and added another bottle of injector cleaner. Then drove up to the Sequouas (235 miles) at 70-75 mph. Ran great had no problems plus i got around 24-25 mpg, never got that good ever.
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