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Of course the fastest way to diagnose this would be to hook it to an analyzer on a hot day.
So many things to go wrong, so little time.
If you were ever in doubt of fuel delivery, a fuel pressure guage is your best bet. The ECT and IAT temperature sensors may have a problem. Vacuum leaks and intake leaks are always a possibility. In cold weather these air leaks tend to make the RPM's cycle up and down.
If there are any other symptoms, they might help to pinpiont the problem.
And, if the CEL has come on, get the codes checked.
