New Plugs - Rough Idle with Misfires

[Run_Amok]

Coyote cognoscenti, regarding my 2014 GT with 25K on the clock:

Background: With the AC on, when the compressor cycles on, there is a drop of 250 RPM, but the car felt like it was strugglling a little to regain RPMs. A friend suggested new plugs (the car previously ran on California gas).

Issue: We replaced the factory plugs with Motorcraft units, and immediately she idled roughly. We connected a scan tool (Snap On), and witnessed misfires on cylinders one and three (only at low RPMs). No codes present and no CEL.

I will appreciate your thoughts on why this happened.

 

[TMSBOSS]

Did you check the gap on the new plugs?

check all the connections at the coils.

Have you driven it yet!

 

[Run_Amok]

Did you check the gap on the new plugs?

check all the connections at the coils.

Have you driven it yet!

I am 90% confident that the gap is correct on all of the plugs. I will verify.

Checking the coil connections right away.

She runs great off idle. Yay!

I disconnected the battery for 30 minutes hoping to force a relearn. No improvement.

 

[TMSBOSS]

Good luck. Check everything and then run it. Codes may come up with a short drive. They may help in troubleshooting.

 

[mwjscn]

Did you do an idle relearn procedure? It has more steps than just disconnecting the battery.
1. Discharge computer system
2. Reconnect battery
3. Set parking brake
4. Park (AT), Neutral (MT)
5. Start engine and run with no accessories on until it's at temperature for at least one minute
6. Turn on the A/C and let the idle run for another minute (calculates the drag on the system to keep idle stable)
7. Drive vehicle normally for 10+ miles
If it's just your idle that choppy and it otherwise runs fine, give that a shot.

 

[Run_Amok]

It turns out that four of the plugs were improperly boxed. Sigh.

The idle relearn and new, correct plugs have helped with the compressor-on stumble, which now occurs every third cycle on.

Thank you all again for your help!

 

[TMSBOSS]

Yea…. With new parts a trust but verify approach is a good idea. Did they send the right part?? You have to check behind everyone unfortunately

 

[Run_Amok]

Yea…. With new parts a trust but verify approach is a good idea. Did they send the right part?? You have to check behind everyone unfortunately

Yep. Will do that moving forward. Interestingly, the individual boxes showed no signs of being previously opened...