I have an rough idle issue after changing COPS and plugs, I think I may have a weak COP, not throwing any codes, is there any way to test them?

 

I hope this helps. I took my 99 Expedition with the 5.4L in to have the spark plugs changed on Saturday. It seemed to run fine when I took it in. The mechanic at the delaership told me the plugs were good but I had just purchased the vehicle and did not know how long ago they were changed. He also let me know that one of the connections to the COPs was not plugged in tight when I brought it in. I noticed that the vehicle ran a lot smoother after the plug change. I would check to see if all of your wires to your COPs are plugged in tight. If one was bad or completely disconnected I was told it would throw a code and the check engine light would come on. Good luck.

 

Are you sure you didn't knock a vacuum line off, or damage one while you were changing the plugs/COPs?

You can unplug the connector on the COPs one at a time and see if there is one that does not effect the engine when it's disconnected. If you find one, that's the culprit.

FYI - You will get a CEL from disconnecting them, but it will go out on it's own when they're all reconnected.

 

I changed out my COP's and in the process I broke the bracket for line from the brake booster to the IM {hard line from IM/changes to rubber hose halfway to BB} and it left two pin holes {vacuum leak} that threw my idle off. It surged and stuttered at idle but ran smooth as silk under load. Check and make sure there are no vacuum leaks and all your connectors are plugged back in.

 

You can test the primary and secondary resistance of a COP. The procedure is detailed in Haynes for Expeditions. I don't remember the specs off the top of my head. But, using an Ohmmeter, you can test them. Of course, as mentioned, a way to troubleshoot is by moving the COP. Is it bad enough that it throws a code?