'97 2.0L 4cyl odd miss

Several months ago I purchased a 1997 Dodge avenger with <70000 miles on it. Currently it only has 76500 on it. It ran nice at the time but does
use a bit of oil. About 2 months ago the car started carrying on at less than 2000 rpm it would miss when given gas but idled smoothly and above 2k rpm would run smoothly or at least I didn't notice a miss initially but the rpms that it would be noticable on started to creep up.
I figured that this was probably spark plugs and bought a set of the basic Bosch platinum plugs gapped them at probably a bit under the about .05 the car calls for as I only had a .045 at the largest feeler gauge. Anyway this corrected the problem or at least appeared to. The old plugs looked ok, what appeared to be normal wear anyway at least on the electrode, the insulator on the plug looked a bit burnt though where it wasn't covered by the boot.
However recently this problem has reoccured. I haven't had a chance to pull the plugs and look at them but as it has been only about 3000 miles I'm wondering if there is anything else I should be looking at. I don't believe that I drive the car in a manner that would cause the plugs to die this quickly. I also did consider that it might be the fuel in the car and put about 5.5 gallons of 92 in though I had been using 87 constantly.
The check engine light is not comming on but I have no way to attach the car to a diagagnostic device without spending a lot of money so I'd like to avoid that a bit. Unless someone knows a way to read the codes without it like you could do in most older cars?
Thanks Tim
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those Bosch Platinum plugs and install the correct plugs and gap them at the proper spec. Then install new wires
Glenn Beasley Chrysler Tech
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i had a 2.0 that started that way and it was not the plugs or wires it was the egr valve sticking check that to Tim wrote:

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