My '04 MCS has @126k mi on it. I decided it was time to replace the plug wires, mostly as preventive maintenance. After installing the Magnacor 8.5 wires two days ago, many seemingly unrelated little issues disappeared. I can't promise that they all were fixed by new plug wires; this isn't a "scientific" test, but so far...

My MCS has poly control arm bushings and engine mounts. The drivetrain is pretty tight. What others describe as yo-yo, was for me a higher frequency jerking hesitation. With almost any throttle on or throttle off transition...boing, boing. After the wires, nearly gone.

I had been getting the wheel speed sensor warning light "trifecta" almost daily. I was planning to diagnose which sensor was failed and replace it, but after the wires, no trifecta in two days.

I've also had an idle problem where at a stop light, the idle would drop and almost stall, over-recover to @1,500 rpm and repeat every second or two. When I'd watch the ignition timing on the Scangauge, it was all over the place; +33 to -8 to +10 to 0, etc. This is what got me thinking about ignition wires. Since changing them, the idle has been rock steady.

I think it's possible that these seemingly unrelated things could have been fixed by new/better plug wires. I've added several LED indicator lights on the dash. One to replace a high beam indicator that went south, others for front and rear fogs. With the engine running, these LEDs would flash randomly for a fraction of a second with no particular pattern or regularity. I got used to it and didn't mind it, but I've now noticed it's stopped doing this.

My conclusion, which could be wrong, is that the old plug wires were in fact "bleeding" voltage; not shorting per se, but leaking. I'm guessing that the leaking voltage is what was causing the LEDs to randomly flash, could have been causing the idle instability, and could have caused or contributed to my wheel speed sensor trifecta. The wheel sensors are also called "pulse generators". If ignition pulses were leaking out the ignition wires, couldn't they be picked up by wiring or sensitive sensors looking for tiny pulses from a "pulse generator" (assumed to be a magnet passing a sensor)?

 

Be sure to check that the coil posts are clean and not corroded. I also have Magnacor's but never felt any difference. I changed to them at 50,000 just because....

Glad to hear the the "issues" are gone.

Rich