RPM dropping at idle and then Recovering. Inconsistent

[belmont]

Hey guys, new here. I’m having an issue with RPM dropping to 300 and then coming back up to normal Intermittently. I had a cylinder 6 misfire code but had just changed plugs and boots with motorcraft about 1500k miles ago. Went ahead and swapped out the #6 plug with a new one and the code cleared but I still have the random idle issue. Might be good one day and worst the next. New mass airflow and filters all done 1500k ago. The plug I pulled had some corrosion at the tip and the ceramic was yellowed near the base. Any thoughts would be appreciated. Engine is not pushed hard and has 178k on it. Also cleaned out throttle body at the time all the other work was done.

 

[99WhiteC5Coupe]

Hey guys, new here. I’m having an issue with RPM dropping to 300 and then coming back up to normal Intermittently. I had a cylinder 6 misfire code but had just changed plugs and boots with motorcraft about 1500k miles ago. Went ahead and swapped out the #6 plug with a new one and the code cleared but I still have the random idle issue. Might be good one day and worst the next. New mass airflow and filters all done 1500k ago. The plug I pulled had some corrosion at the tip and the ceramic was yellowed near the base. Any thoughts would be appreciated. Engine is not pushed hard and has 178k on it. Also cleaned out throttle body at the time all the other work was done.

Year, make, model & engine?

Since you replaced all spark plug with OEM Motorcraft ones, I would use one or two tankful of Techron fuel injector cleaner according to the label directions.

 

[belmont]

2012 expedition limited 4x4 5.4 engine.

 

[belmont]

I have done a few bottles and hasn’t seemed to do anything. I guess the next step would be replacing the injector?

 

[99WhiteC5Coupe]

I have done a few bottles and hasn’t seemed to do anything. I guess the next step would be replacing the injector?

Is there a code being set since you changed the plugs and coil (and used the injector cleaner)?

You may want to next carefully inspect all vacuum hoses for a leak, paying attention to the ends where they plug into connectors - where they are more susceptible to splitting and leaking.

If that doesn’t work - replacing the injector may be next. Good luck.

 

[Homer]

Surging could be caused by a vacuum leak. Check the vacuum lines. Probably could try the smoke test to find it.

 

[Bruce Mitchell]

I agree with the previous suggestions; sounds like a vacuum leak somewhere.