My 92 Explorer w/175,000 mi has developed a intermittent miss and knock that I can't seem to track down. Miss occurs at all operating Temps and rpm's. Tach fluctuates 200-300 rpm when held at 1500 rmp in Park. Knock occurs under load on highway, not as bad with 91 octane. Been to a reputable shop two times and scan showed no codes. Suggested replacing battery cables(?) which I did. This solved my jumping amp gauge, but not the miss and knock. Second time shop recommended Intake cleaning, plugs, wires at $300.00(ouch!) I let them because I was out of town. Miss and knock came back after a week. This is a daily driver so I can't let it sit in a shop and accumulate charges for things I can do myself. After reading hundreds of posts here(THANKS for the SITE!), I cleaned the IAC(KUDOS to Wolfmeister), replaced the MAF and TPS. (costs less than the 2 hrs diagnostic at the shop). No difference. My next suspect is the Coil pack, But I just shooting in the dark Now, especially with no codes to troubleshoot. I have noted the Temp gauge seems to swing back and forth in the operating range kinda frequently( every 5-10 minutes at highway speeds) but new thermostat and waterpump about 12 months ago. Yes I tested the thermostat before installing, been burned on that one before. Is this fluctuation normal? Could the ECT sensor be suspect? I am armed with a digital multimeter and a Haynes manual, but You Guys and Gals out there seem to be my best hope of avoiding large shop bill and rental car charges!
Thanks for your suggestions.

 

Have you tried a cylinder balance test? That would determine if the miss is isolated to one cylinder, or spread over all cylinders.
Another basic diagnostic test is fuel pressure.

 

Run a can of BG 44K in the gas. It'll take 300 miles to see the diff. Then report back.

 

Sorry for the slow response, Sat. is my only time to tinker. Thanks for your responses! I had a thought Thurs and checked the original shop ticket. Sure enough they only changed plugs not the wires! Bought plug wires Friday and changed the Saturday. Coil read within specs, but one plug wire(number 5, I think) was dead as a popsicle stick! With all the electronics and sensors, I forgot to check ALL the the basics! Good lesson.

Since I had already bought the BG44K, and checked out the info on the Internet, I went ahead and added it. If the information is correct, this stuff should clean out my injectors pretty good, Right?

 

Yes, it will clean them and the valves etc.