Occasional rough idle, anyone else?

[MLM54]

@MLM54 @Rusherific I know it's a long shot but I've got a similar issue and figure it's worth checking.

Surprised I got an email on this thread! I was never able to determine the culprit. If it makes you feel better, I had the car around for another ~18 months and ~12,000 miles and didn’t encounter any subsequent issues. Unfortunately had to part ways with the fun car for a bit due to life changes. Best of luck @935k3

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[galaxy]

Sorry if this late and repeated, but the car has a, what I would call, two step/two phase idle (best term I can think of. Yes, I know what a two step is). When you are sitting still, clutch in, foot off the brake, there is a programmed idle speed. If you put your foot on the brake, there is a second programmed idle speed that is even lower. It’s extremely low. Feels like it’s gonna fall on its face sometimes. Completely normal, albeit annoying. It’s designed to raise the idle slightly when it knows you removed your foot from the brake and are about to get underway.

I had my tuner completely taken this feature out, plus raise the hot idle speed up a good bit for a little stronger hot idle and better transition to getting under way. Tune fixed it right up and got rid off all those symptoms.

If that normal, two step idle isn’t what you guys were talking about, I’ll go back to my regularly scheduled program already in progress.

 

[935k3]

Surprised I got an email on this thread! I was never able to determine the culprit. If it makes you feel better, I had the car around for another ~18 months and ~12,000 miles and didn’t encounter any subsequent issues. Unfortunately had to part ways with the fun car for a bit due to life changes. Best of luck @935k3

Didn’t expect such a quick response. Glad to hear you didn’t encounter any further issues but the idle thing is a bit annoying.

Sorry if this late and repeated, but the car has a, what I would call, two step/two phase idle (best term I can think of. Yes, I know what a two step is). When you are sitting still, clutch in, foot off the brake, there is a programmed idle speed. If you put your foot on the brake, there is a second programmed idle speed that is even lower. It’s extremely low. Feels like it’s gonna fall on its face sometimes. Completely normal, albeit annoying. It’s designed to raise the idle slightly when it knows you removed your foot from the brake and are about to get underway.

I had my tuner completely taken this feature out, plus raise the hot idle speed up a good bit for a little stronger hot idle and better transition to getting under way. Tune fixed it right up and got rid off all those symptoms.

If that normal, two step idle isn’t what you guys were talking about, I’ll go back to my regularly scheduled program already in progress.

unfortunately it’s still felt at higher rpm. I want to say it occurs (or is noticeable) at anything below 1500 rpm. I’m not sure if mine is unique at all but it’s a slight shudder every 10 seconds or so, dips maybe 25-50 rpm and the a/f guide shows lean. It gets a little worse ant operating temps.

 

[galaxy]

Any chance or opportunity to go check out another car and make a direct comparison.

 

[GJarrett]

Wow what a dead thread resurrection. As @Reddirocket27 aluded to in post #25 it is actually a common problem at least for EcoBoosts. It gets worse and happens more often on a full tank, and the culprit is a cheap and easy-to-replace part called an Evap Purge Valve. I wonder if GT350s have an Evap Purge Valve(?)

 

[935k3]

Any chance or opportunity to go check out another car and make a direct comparison.

Hoping to find someone local to compare.

Wow what a dead thread resurrection. As @Reddirocket27 aluded to in post #25 it is actually a common problem at least for EcoBoosts. It gets worse and happens more often on a full tank, and the culprit is a cheap and easy-to-replace part called an Evap Purge Valve. I wonder if GT350s have an Evap Purge Valve(?)

I’m just not experiencing the other symptoms tied to that like smelling unburnt gas or difficulty filling the tank fully. Still might be worth checking out I guess.

 

[GJarrett]

Mine did the thing where the rpm dips at idle at redlights and I never smelled any gasoline fumes. Replacing that part fixed it for me. There was no problem filling the tank; it just happened more often with a full tank.

 

[935k3]

Mine did the thing where the rpm dips at idle at redlights and I never smelled any gasoline fumes. Replacing that part fixed it for me. There was no problem filling the tank; it just happened more often with a full tank.

Good to know. Appreciate the input.

 

[Balatgek1]

Intermittent idle drop and Air/Fuel ratio fluctuating. (5 second mark) I had this issue for over a year now, there is no CEL. I replaced the spark plugs (tried gaps for 19/20 and earlier 350's), the Evap Purge Valve, and the PCV valve. The wires to the Variable Valve Timing solenoids appear to be in good condition.

The dealer conducted some tests but could not find anything wrong and suggested a possible clogged fuel injector. He added a can of BG44 fuel system cleaner. Then I added another can of BG44 and used top-tier gasoline for the rest of the summer, but the problems still there. I have noticed that some S550 GT owners experience idling issues were due to faulty VVT solenoids.

 

[526 HRSE]

Does it only do this when it's cold or when it's warmed up also? The video above shows oil temp at 160.

 

[Balatgek1]

Both, definitely more noticeable when it's warm.

 

[526 HRSE]

could be something simple like a dirty MAF sensor?

 

[Balatgek1]

Thanks, cleaned that twice.

 

[526 HRSE]

Thanks, cleaned that twice.

Replace it?

 

[Balatgek1]

Worth a try. Won't know till after hibernation season.

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