I have brought my truck to the dealer a couple different times for rough idle.
once they found a vacuum leak and repaired assuming the problem was solved.
second time they said the it is slightly out of spec and I should change the plugs. It may have something to do with my roush aftermarket intake.
I’m just wondering could the intake actually cause this?
Is it reasonable for me to change plugs at 32k on my dime?
This truck never idled real smooth from day one and I think it’s worse now, hard to say.
2021 F150 3.5
I’m not really happy with the quality as of now I’ve had several issues. Thursday it goes back in for a resonator replacement due to a rattle internally.

 

if it's had a problem from the start, I'd put it back to stock until the issue can be resolved so they dont have anything else to blame.

they should be able to clarify what "idle slightly out spec" means - wrong rpm? misfires? What exactly is "out of spec"

If youve got any mechanical ability it doesn't take long to change the plugs yourself but I would want a better diagnostic than that.

 

Plugs are roughly $50 and take 40 min to change. These F150's are the easiest vehicles ive ever changed plug on.

Lots of tuners will tell you to change plugs at 30k on the ecoboosts tuned or not...obviously we all know what the manual says.

If there is an issue, why are they trying to charge you to fix it? Are they saying the plugs are a wear item and thats why? I only tell people to change their own plugs if they have the tools, the patience and a torque wrench...they break easy

 

To answer your question "Could my after market intake cause this". Yes if it has a small vacuum leak any where it will cause a rough running engine. Too much air not enough fuel. If you want a quick sanity check.

Get a can of starter fluid. Spray around the intake and see if it idles any better or rev's up. If it does you have a leak and need to fix it.

As for the plugs at 32K miles, to me that is a little to soon to be changing them. I normally wait until 50 or 60K miles to do them. I know it says 100K, but I have run a 2.7 over 306,000 miles with out issue doing it this way.

 

Why did you put an aftermarket air intake on to begin with?
If its just a cold air intake that is completely pointless.

 

I looked at the Roush one and it actually still pulls air from outside unlike a lot of the cold(hot) air intakes, and it does have more filter area. But it really shouldn't cause any issues unless he created a leak after the MAF somehow. Still probably pointless

 

lots of aftermarket cold air intakes have caused idle issues, engine codes, and other issues with these trucks.

not debating whether they do anything or not, but if I’m having idle issues, first thing I’d do is put the stock intake back on and swap plugs.

 

Factory air intake is more that sufficient. And if you look where it pulls in the air, its not hot air.

 

38000 for a plug change? Why not! Particularly if it's an Ecoboost. DIT cost is near what a oil change is. I run a tuned 2.7 and swap plugs at 20000.
Far as the intake some can cause trouble some do not, Most often the problem is a simple fix. While the stock CAI is very good I have no problem with dressing up the engine bay.
KM

 

You must be relatively young... pre late 1990's, specifically with Fords, pre the mod motor, spark plugs were a trivial thing. No coil packs, no intake manifolds in the way...

Ford 300-6 and 2.3/2.5 4 cylinder or even the 302 and 351's were ridiculously easy to do,. The biggest fear was when pulling the plug cap off, that you might pull the leads out of the plug wire...