Ford Mustang Ecoboost Rough Idle

Jroy333

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I have a rough idle on my ecoboost. Nothing crazy, not to the point of stalling, but I can feel the stutter that seems to be common with these motors. I have replaced the low-side fuel pressure sensor, the EVAP purge valve, coils, plugs, and dove into the intake manifold and intake valves and gave them a cleaning. I dove into the cylinders with a boroscope numerous times. I checked the turbo wheel and no play, checked my oil levels and steady as she goes. I check my coolant about once a week for four weeks now and no drop. I check my exhaust every now and then and no smoke. I highly, highly doubt it's a head gasket. there's literally no sign at this point. I have just a cold air intake and a bigger intercooler but no tune so I couldn't blame a tune for the idle. I just always really liked the way Front-Mounted intercoolers look and never really cared to have it tuned. I have the stock intercooler and air intake in case I need to bring it in. I was told by my dealership (Koons-Sterling) that if there are no codes, it's hard to chase down. They checked my computer and no history of any misfire DTCs.

My question is - is this just normal for the four-cylinders to run like this?

It's a 2020 with 16k miles and I took the valve cover off to make sure everything is ok in there and these engines have some aggressive cams. Not race-level, but enough to make them idle similar to a cammed engine. It always had this stutter but I put BG syncroshift into my transmission and noticed I can feel it much more pronounced through the shifter. it's like a slight stumble every 20 seconds with a rough idle while running and nothing near enough to hurt anything. No weeping in the cylinders and the pistons and valves look great, thank you UPR!

Anyone have a direction to point in?

I've only put AMSOIL signature series and shell fuel since ownership and this is kind've pissing me off because it is hard to tell if this is normal or not. Runs perfect besides this weird rough idle.

 
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Jroy333

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Also just ran the engine's PCM self-test through ForScan. No counts whatsoever in the general misfires area and through cylinder's 1-4. I either have a bad motor mount (at 16k.... I might sell my car if it does lol) or I am just all too picky on idling.
 

njweatherman

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Joseph,
When the rough idle occurs, are you at a red light or stop sign? What is your normal idle speed when the car is in drive, fully warmed-up, and at a red light?
 
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Jroy333

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Has a rough idle on start up and goes away. That’s pretty typical for the engines. What I notice at red light and stop signs is a slight skip or stutter. Engine RPM goes from 760 to about 720-740 every 20 seconds and if I idle it long enough, say 3-5 minutes when warmed up, the car brings it’s idle up to 890-910 range. A/F ratio is 14ish. Stays above 14 and the octane adjust ratio stays in it’s appropriate ranges. What are you thinking?
 

njweatherman

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Wow, your idle is a lot higher than mine. When my 2020 Mustang GT automatic is fully warmed up and I am at a red light, my idle is steady around 600 rpms. If I place it in park, it jumps to about 625 - 675 rpms. (BTW - I am fully stock, with the exception of an X-pipe). The problem people are having here on the forum is that the idle will suddenly drop to around 500 or lower and then quickly bounce up 600, and then back down to 500. Some have even stalled at a light. The idle drop also results in the car to shake. Your idle drop does not sound as bad. I'm curious on what others think? Sorry I could not help.
 


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Jroy333

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No worries! The little ecoboosts are Kindve known for a rough idle. Honestly all GDI engines are so I just want to make sure all is well. You can feel it stutter through the shifter and I don’t think I’ve owned a car quite like this so it’s getting used to. Mine is a 2020 as well.

with the GT, there are a few known causes for your idle issues. The evap Purge valve can do it but also the VCT sensors. Check out some YouTube videos on that.
 

njweatherman

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What helped my rough idle was the throttle body and mass air flow sensor cleaning. Since then, the idle has been much better. I'm keeping my fingers crossed:)
 
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Jroy333

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Well I got misfires yesterday while driving. Time to take the CAI off and bring it in. Thank God for warranties
 
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Jroy333

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Brought it in to ford and they said they would not cover seeping head gaskets. It needs to be a failure. So I thinking about possibly opening up my head and putting a gasket in myself
 

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Also just ran the engine's PCM self-test through ForScan. No counts whatsoever in the general misfires area and through cylinder's 1-4. I either have a bad motor mount (at 16k.... I might sell my car if it does lol) or I am just all too picky on idling.
Was your motor mount okay ? Mine leaks a watery liquid so I guess needs changing.
 

 
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