Changed spark plugs. Now rough idle.

[2009Limited]

Hi all

I have a 2009 Ford Expedition 4x4 Limited with about 165k miles. I was having an issue with acceleration hesitation and stuttering going up steep grades on the highway. So I changed the spark plugs and spark plugs only. (Thank the lord for FordTechMakuloco).

Good news is she no longer hesitates when I let her rip. However, now she has a rough idle where she didn't before. It seems to be worse when cold and not as bad if she's been all warmed up, but still noticeable. Oh and I should mention she threw a code when I was having the hesitation issue P0420 (Catalyst System Efficiency Below Threshold Bank 1). It has since been cleared and not come up again.

Any ideas?

 

[99WhiteC5Coupe]

Hi all

I have a 2009 Ford Expedition 4x4 Limited with about 165k miles. I was having an issue with acceleration hesitation and stuttering going up steep grades on the highway. So I changed the spark plugs and spark plugs only. (Thank the lord for FordTechMakuloco).

Good news is she no longer hesitates when I let her rip. However, now she has a rough idle where she didn't before. It seems to be worse when cold and not as bad if she's been all warmed up, but still noticeable. Oh and I should mention she threw a code when I was having the hesitation issue P0420 (Catalyst System Efficiency Below Threshold Bank 1). It has since been cleared and not come up again.

Any ideas?

A rough idle can be caused by a dirty throttle body bore, or even a small vacuum leak.

Did you move or disconnect any hoses during the spark plug change? I would systematically check all your work, include the hose connections, any clamps, etc. Also, check the inside of the throttle body bore (and clean it if dirty).

 

[Hamfisted]

Yeah if you can't easily identify a vacuum leak I would recommend smoke testing the intake system.

Smoke Tester on Amazon


.

 

[2009Limited]

The 3 way connector for the heater hose did start to leak severely during activity and a good bit of coolant did drop down on the left hand bank (passenger side) before I even started working on that side. I was able to replace that and then air sprayed off the left side to replace the plugs. I did go back over and check all of the connections but probably worth another go around.

 

[Dennis_H]

My dad just had a similar issue on his V10 motorhome. Ran great down the highway, but idle was really bad. Turned out to be EGR valve. Didn't throw a code, but caused some real bad idling. Wasn't closing all the way, but now it runs great.

 

[dcsang]

Did you replace with OEM plugs?

 

[2009Limited]

I used these

https://smile.amazon.com/gp/product/B071R4TNYX/ref=ppx_yo_dt_b_asin_title_o05_s02?ie=UTF8&psc=1

 

[Trainmaster]

Since the rough idle started after changing the plugs, I'd say a plug, connector or boot is your problem. If you have access to a code reader that shows misses by cylinder, it will save you much work. Otherwise I'd start with the cylinder that got watered on. Take out the plug, check it, replace the boot. Check all your connectors.

I always replace the rubber boots when I replace plugs. They can short to ground with a small carbon trail.

Then as C5Coupe suggested, there are vacuum things...

 

[dcsang]

All the suggestions you have received thus far are valid and should be checked thoroughly. It is my opinion that you should purchase a replacement set of Motorcraft plugs from a reputable source if you hit an impasse.

I am skeptical of purchasing OEM parts from third-party sellers on Amazon and reviews of that very product suggest buyers received non-genuine plugs that did not perform well or failed prematurely.

 

[2009Limited]

All the suggestions you have received thus far are valid and should be checked thoroughly. It is my opinion that you should purchase a replacement set of Motorcraft plugs from a reputable source if you hit an impasse.

I am skeptical of purchasing OEM parts from third-party sellers on Amazon and reviews of that very product suggest buyers received non-genuine plugs that did not perform well or failed prematurely.

I think you're right.. I didn't cover the reviews thoroughly. I'm about to hit a road trip for 3 weeks and unfortunately won't have time to check on any of the things mentioned here.

I believe first step is I'm going to clean the throttle body. If that doesn't work, I'm probably going to swap out the spark plugs from a reputable source. If that doesn't work, I'll probably see about this smoke kit to check for vacuum leaks.

 

[07navi]

I just replace the boots that are obviously needed and never I had a problem, they can be cleaned also. The biggest mistake people make is putting too much dielectric grease on them which attracts dirt and moisture and not keeping the plug holes clean. If you do that they should last the life of the truck. I use a rag attached to a wood dowel, carb or brake cleaner, air compressor, and a drill to clean the holes. You can use a light and a little mirror to check how well you did. Just put a tiny bit of grease on the tip of the spring to keep it from corroding.

 

[2009Limited]

UPDATE:

She finally threw a code on Friday. Cylinder 8 Misfire. So I ran to an auto parts store and got 8 new sparkplugs. When I go to take the intake snorkel off, I notice the gasket is bent and folded in slightly.. meaning I don't think I refitted properly from the last time I checked everything.. DOH! This was most likely my issue causing the rough idle, but I went ahead and changed #8.

Everything is running super smooth now. Thank you guys for all of the ideas and input.

 

[Trainmaster]

Thanks for the followup. Nice work. We've all been there.