Stock coyote engine surging at idle

[raidernixon]

Hi all,

I searched the forum and didn't find anything that seemed to be the same issue. Apologies if this already has a topic.

I've got a 2011 GT with the manual transmission. 98,000 miles to date. Bone stock with exception of Roush axle back exhaust.

Battery replaced in July 2014.
A/C Compressor (failed clutch) was replaced in August 2014.


I am looking for a little bit of diagnostics help to determine what might be going on. About 4-6 weeks ago, the car started experiencing inconsistent periods of RPM surging (maybe once a week), with more common and persistent occurrences (multiple times daily) of what seems to be rough idling (beyond that of the typical coyote idle stutter) and minor RPM surging. No engine codes to date.

I have been keeping the car in engineering mode to monitor the RPM surging.

450-1300 RPM is the surge range for the less common occurrence. Each time this has happened has been after a cold start and driving for about 1-2 miles and coming to a stop. There is a noticeable popping sound from the exhaust during the episode.

500-950 RPM is the surge range for the daily occurrence and happens anytime between cold start up, warm start up and idling situations in traffic. You can feel a slight shutter in the car whenever it is going on.

RPM is steady outside of the idle range.

So far, I have pulled out the original spark plugs. They appear to be OK but I am going change them out since they are old and may still be a factor.

I am going to take a look at the mass airflow sensor tonight to see if it might be dirty. Otherwise, I am not really sure what else to check for.

Does anyone have any ideas or suggestions of what else I should check out while I am under the hood and what might be causing the surging?

Thanks in advance for any help.

 

[stkjock]

have you check the alternator?

check/clean the maf as you alluded too

 

[JEWC_Motorsports]

Plugs and maf. Replace and clean. Lol am i the only one who replaces my plugs every 15k miles?

 

[BadHabit2Break]

TB probably needs to be cleaned as well.

 

[Blackmamba07]

Clean maf

 

[black2008gt]

The coyote motor will surge a little. It will kind of feel like someone is pushing on the back of the car at stop. Anything beyond 1-200 rpms and feels more than a little bit of a push needs to be addressed.

 

[JEWC_Motorsports]

Ummmm what?

Mine doesnt surge unless the plugs are bad or the maf is dirty.

 

[onebadgsx]

replace the widebands, most likely these are going bad or already bad. mine does this when they need replacing. im on e85 with long tubes so it happens alot.

 

[Boaisy]

The coyote motor will surge a little. It will kind of feel like someone is pushing on the back of the car at stop. Anything beyond 1-200 rpms and feels more than a little bit of a push needs to be addressed.

Mine only surged under the BAMA tune. Hasn't since I switched tunes. When it was bone stock, it never surged either.

 

[Renesis07]

I'd personally start at cleaning the MAF..... then these.

have you check the alternator?

Plugs and maf. Replace and clean. Lol am i the only one who replaces my plugs every 15k miles?

TB probably needs to be cleaned as well.

 

[RazorbackMustang]

Plugs and maf. Replace and clean. Lol am i the only one who replaces my plugs every 15k miles?

Yes you are.

 

[BadHabit2Break]

Plugs and maf. Replace and clean. Lol am i the only one who replaces my plugs every 15k miles?

I think so.

I am just under 30k and it is just a thought for me right now....lol

 

[JEWC_Motorsports]

I dont buy into the 100k mile plugs, im old school. I bought them in bulk from rock auto when they had a sale awhile back. I have a lifetimes worth.

 

[Bullitt 3309]

I dont buy into the 100k mile plugs, im old school. I bought them in bulk from rock auto when they had a sale awhile back. I have a lifetimes worth.

then add a set to my oil order...

 

[JEWC_Motorsports]

Sure brother, just need my engine cover back. lol

 

[wbt]

Sure brother, just need my engine cover back. lol

You can have mine when we do the gears.

 

[claudermilk]

Here's a stupid question: is the air filter clean?

 

[fiveoh]

replace the widebands, most likely these are going bad or already bad. mine does this when they need replacing. im on e85 with long tubes so it happens alot.

+1 I had the same thing when my o2 went bad.

 

[raidernixon]

Thanks everyone for the tips/suggestions.

I finally had time to dig a little deeper into the issue this past weekend and found several issues.

Upon further inspection, the spark plugs for the #6 and #8 cylinder looked questionable and were prob ready to give out it they haven't already. I replaced all of the plugs.

I pulled the MAF sensor and found a little bit of contamination on the sensor wire along with the throttle body. I cleaned up both of those and replaced the air filter.

After reconnecting the battery I let the car relearn it's air/fuel idle trim.

The issue seems to have resolved and the car even feels a bit stronger now. Shame on me for pushing the plugs and MAF sensor maintenance to the limits!

 

[mrgtx]

I dont buy into the 100k mile plugs, im old school. I bought them in bulk from rock auto when they had a sale awhile back. I have a lifetimes worth.

That was a pretty good call there. Had I been paying attention, I might have stocked up too!

That said, changing them more than often is possibly not a great idea since you're introducing some risk each time from possible FOD issues...or just wear and tear of torquing steel threads into an aluminum head.

I'm sure that a bit of care will prevent these problems but sometimes it's not worth the risk, even when the risk is tiny.

Just my opinion.