5.0 Rough Idle issues

[Ayee__Jay]

My GT was doing this, I changed the spark plugs good as new !
change the plug gents!

Running on 80k definitely time for a tune up with a lot of things and thought I should definitely start there, will try it! thanks!

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[Bullit69]

I did my tune up at 32kkk, I think these cars are hard on spark plugs.

I may add last oil change I ran some certec, I’ve also read it’s not a bad idea to clean the throttle body.
I’ll clean the throttle body shortly along with the mass air.

Be sure to use specific cleaners for the throttle body and for the mass air.

 

[FlaGrey]

I dealt with this for awhile. It finally gave me a p011 code just one time during a stall at a light.

I replaced all 4 VCT solenoids

However I should mention that the battery was disco for a few days during this time.

 

[Cobra Jet]

Most common causes of S550 5.0 rough idle:
IMRC problem
VCT issues
Cracked or loose vacuum lines
Spark plugs

The IMRC and VCT - there's a lot of tech in here for those and how to resolve. Here's (2) IMRC threads to get you going:

The failure is occurring with the actuator rod that is integral to the intake. The rod snaps, which renders the actuation of the IMRC plates useless and in-op. Check this thread and Post #15 for the picture of what I am referencing::
https://www.mustang6g.com/forums/threads/our-first-dtc-p0308.160243/

How to replace intake manifold due to IMRC failure:
https://www.mustang6g.com/forums/th...d-replacement-oem-how-to.167226/#post-3402800

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(2) Threads for VCT info:
https://www.mustang6g.com/forums/threads/2015-2021-s550-5-0’s-ssm-50067-vct’s-again-various-dtc-codes.169419/

https://www.mustang6g.com/forums/threads/p0018-code.123932/

 

[Ayee__Jay]

Not ignoring what you guys are saying at all just wanted to add a little more information to what I've learned. I had a friend with a 2019 who had the same issue and he got an oil change and changed his intake filter and he said it's been running fine ever since. One thing that I have learned from my issue is, it happens more so when I am on a quarter or less of a tank. Could it be the fuel pump? My car is at about 83K miles. I had planned to change spark plugs and all 4 solenoids but wanted to check before I pulled the plug on them. Again, no codes have ever popped up and the car has stalled on me once.

 

[njweatherman]

My 2020 Mustang GT, California Special, 11k, has had the idle fluctuation happen 3 times already since the New Year.
For instance, I will be sitting at a light with my foot on the brake. My idle will be around 600 and steady. Suddenly, I will feel the engine become weaker and the idle quickly drops to 500, but then goes right back to 600. It will do this back-and-forth battle until the light changes. When I get to the next light, the pattern repeats itself. The odd thing is it will do it at 2 or 3 lights, and then suddenly go back to normal. The idle will be fine for the rest of the trip. The last time it happened was yesterday. Today, it ran totally fine.

Thankfully, I have not stalled. No codes yet either. I'm trying to figure out a pattern with it, but so far nothing. I only use 93 octane gas from Shell or BP.

 

[Strokerswild]

My F150 just got out of service jail today. Both intake cam phaser solenoids were replaced, as the dealer was seeing erratic operation with both. Hopefully this is the end of the nonsense with this vehicle.

 

[Ayee__Jay]

My F150 just got out of service jail today. Both intake cam phaser solenoids were replaced, as the dealer was seeing erratic operation with both. Hopefully this is the end of the nonsense with this vehicle.

Any update? How has it been since?

 

[Strokerswild]

Any update? How has it been since?

It's been great, in terms of this engine issue. That I now have a leaky front strut is a different problem....

 

[TheShit]

So this happened to me and my car was brand new. It idle as if a large set of cams were installed and tuned like shit. I took it to the dealership and they said, "it's fine" which was complete bullshit. It went into limp mode 2 times while going through a drive thru and that was before the car had 1000 miles on it. I checked all the normal things like vacuum hoses and reset the pcm, still no change.

What finally fixed it, was replacing the intake. When I pulled off the old intake, I didn't notice anything wrong, but something must have been. Because once I put the new intake on, the car idled smooth with no drops in RPM etc. Just something to think about.

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