Just had mine changed today Plugs and wires and mechanic discovered top of plug was cracked inside Cap and my vehicle could do 75MPH on highway & appeared to idle ok. But every now & then I would get a warbled idle and when I press down on peddle at 2000 rpms I could tell there was misfire...
Had the same problem with mine today.. 91K miles, replaced Plugs and wires.. found that #4 Plug was broken inside the boot cap where porcelain meets electrode. Replaced that and fuel filter everything is purring now. javascript:insertAtCursor(document.forms['MESSAGEFORM'].MESSAGE,':supercool:')
Got rid of the Wrangler RTS (2nd set) at 30K miles... Dealer replaced first set at 10K miles because I had proof from Sams Club I had rotated them at 5K miles after I bought truck & they still had cupped by 10K miles. When 2nd set wore unevenly I went straight to Sears first & replaced all...