Got rid of that little idle bump - finally

[ocrick]

I have been chasing a slight bump (rough) idle for about 6 months...did all the typical stuff. Cleaned throttle body, reset TPS, Replaced plug wires, cap rotor and coil. All no help...until today.

I pulled out the Bosch +4s and replaced them with my old AC Delco Rapidfire #5's and got a perfect idle!!!

The Bosch plugs looked ok....so I pulled out my digital meter and measured the resistance between the plug wire connector and the firing point in the center of the insulator. Found that 6 of the 8 had resistance between 4 and 5k ohms. The other 2 had resistance of 71K and 238K!!! ad

I suppose that if you make sure that they match and install them you will be ok....but from here on out it's AC Delco for me.

 

[Robertwav1]

I didn't realize that there was a resistance between the electrical path of the spark plug. Learn something new all the time. Wonder why they was such a difference?

 

[ocrick]

Resister plugs are needed to reduce or eliminate radio noise. As to the difference.....there is no excuse. Purely defective manufacture. I thought Bosch made good stuff. I guess not always.