Coyote Rough Idle

[Bullitt0819]

I've got about 3,500m on my '19 Bullitt, and may have encountered a potential problem: On a hot day--near 100degF--sitting at a couple stoplights, the engine started running noticeably rougher. No movement on the tach--I think the ECU will keep idle steady no matter what it takes--no CEL or other indication and it didn't threaten to stall, just noticeably rougher than usual. This happened twice, but once I got moving it smoothed out. It's been even hotter--105 a couple times--and I didn't have this issue. No 'ticking' or 'rattles,' at least none that I've noticed and I'm pretty sensitive to engine noise.

Anyone else seen this behavior?

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[showbbq]

Hasn't happened to me, no. I'd do the basics...check the gas you're using, make sure all the hoses are snug, unplug the battery for a couple of min, have the dealer check for issues and make sure the ECU is up to date.

 

[NoVaGT]

....I'm pretty sensitive to engine noise.....

Here's your answer.

Yes, vehicles will shake and shudder here and there. They have continuous feed-back loop control systems, they adjust themselves to changing conditions. High heat means your IATs are high, the car might be adjusting to them.

And your AC compressor is probably also switching on and off, making some load changes to the engine, which causes more adjustments to occur.

Relax. Stop over-reacting to every little thing. If you're expecting your car to run like a sewing machine 100% of the time, you're going to disappoint yourself. Cars shudder, whine, roar, get hot, and do other stuff.

 

[Bullitt0819]

Here's your answer.

Yes, vehicles will shake and shudder here and there. They have continuous feed-back loop control systems, they adjust themselves to changing conditions. High heat means your IATs are high, the car might be adjusting to them.

And your AC compressor is probably also switching on and off, making some load changes to the engine, which causes more adjustments to occur.

Relax. Stop over-reacting to every little thing. If you're expecting your car to run like a sewing machine 100% of the time, you're going to disappoint yourself. Cars shudder, whine, roar, get hot, and do other stuff.

No, I'm not 'overreacting.' I've driven this car daily for seven months--mostly along the same route to my mother's and back--in hotter weather, with the AC on 'Max' or high most of the time. I'm not worried--yet--about an engine tick or rattle, and this came on as a total surprise (it is a noisy engine, but none of the sounds have given me any concern). This isn't a noise, it's a discernible roughness--you can feel it in the 'seat of your pants'--in the engine that comes on instantly and, so far, only goes away when I accelerate from a stoplight. Temp and other indications are normal.

I think the previous commenter is on to something: I had topped-off on gas--about half a tank--in the morning. I put about 8.5g of Costco Premium (91-octane) in it. Costco gas is allegedly 'Top Tier' and I've used it, when convenient--i.e. when the lines aren't long--in several cars for years and not had any issues with it. I'm gonna run this tank out and fill with Chevron* Premium and see what happens.

* FWIW, my engine builder, who's a well-known local race engine builder and who's built several engines for my dad and I, told me the engines that come to him whose owners use Chevron exclusively are in the best shape. He uses it exclusively although it's as much as $0.40/g or more more expensive than Costco.

 

[el-guapin]

I would say if it you are concerned, make an app with the dealer to have it check. It might be the beginning of something or it might just be nothing.

 

[Bullitt0819]

Drove it today under same conditions. Didn't notice any roughness, therefore none exists.

Thanks for the replies.

 

[el-guapin]

Drove it today under same conditions. Didn't notice any roughness, therefore none exists.

Thanks for the replies.

 

[GreenS550]

You might laugh on this but here is a story. Back in the mid 70s my little sister had a '70 Duster with the slant 6 engine. When that car's oil got a lot of miles on it (2,000+) it would stall at most intersections. Change the oil, good to go. Great car and she put lots of miles on it, but when it started stalling at an intersection, time to change the oil. Did this repeatedly over the years she owned it.

Since I drive my '19 Bullitt pretty hard daily, I am changing the oil every 2K miles. It's got nearly 4K on it and time for its second change. Going to do the transmission and rear axle as well.

 

[Bullitt0819]

Got the roughness again for a brief period today. It was warm--about 95deg--but not as hot as the other day. Again, I was sitting at a stop light and felt the roughness, and the idle RPMs went from the typical 600+ up to a little over 700. A/C was on MAX, so that likely has something to do with it, but it doesn't happen consistently and my '08 Bullitt never exhibited this behavior. The revs going up a little, I can understand, but the roughness isn't kosher IMO. Still on the same tank of Costco gas, and it'll be a couple days before I run most of it out, then I'll try a tank of Chevron.

 

[GreenS550]

I;m guessing it's just the tune. Believe it or not, the Steeda tune made my car run smoother and idle as good or better than stock. I think your car is OK. I had a 2009 Bullitt (left over '08) and that car only had a cai and tune. Ours has the GT350 intake and therefore a unique calibration on the tune. It's entirely possible that Ford has a fix for it by now.

I can remember many other Mustangs I owned not idling consistently.

If you take to the dealer, please update us on what the results were.

 

[Bullitt0819]

Not worth a trip to the dealer--yet--because it's intermittent and not reproducible. But, I get an oil change in a couple months and I'll bring it up then.

 

[Andy13186]

I have this problem, I had my car on e85 when it started and it actually threw a code p0030 for o2 sensor, but then I switched to the stock tune and ran 93 and it came back on. I took it to the dealer and they replaced the sensor and I drove home and on the way home it stalled again while I was on pure 93 octane and the stock tune and the new o2 sensor. So now I went back on e85 hoping for a different code but it hasnt thrown a code for 3000 miles. I still have this issue and I am not sure what caused it, I do think it may have started with the temperatures warming up here in florida possibly. My car has only actually stalled twice but it has come close and ran rough many times, a few times a day most days at redlights it goes rough. And a few times when im getting ready to pull out into traffic it has gone rough, which is pretty nerve wracking.


My only mods are a JLT catch can, electric cutouts, and a K&N drop in filter. and the e85 tune. Tuner says everything looks fine on the logs and I cant seem to get another check engine light.

 

[831Bullitt]

My 2019 Bullitt will do the same thing on hot days. I noticed it for the first time last week when the temps were around 95 F. No other noticeable changes so I wasn't worried. Also, a YouTuber did a bore scope on his 2019 GT with a couple thousands miles on it. He was having the rattle/knock noise kind of loud. Everything looked fine on his engine so I imagine Ford is correct when they are saying that's just the way these motors sound. Mine does the noise from 2k-3k RPM.

 

[Bullitt0819]

My 2019 Bullitt will do the same thing on hot days. I noticed it for the first time last week when the temps were around 95 F. No other noticeable changes so I wasn't worried. Also, a YouTuber did a bore scope on his 2019 GT with a couple thousands miles on it. He was having the rattle/knock noise kind of loud. Everything looked fine on his engine so I imagine Ford is correct when they are saying that's just the way these motors sound. Mine does the noise from 2k-3k RPM.

Did you have the AC on MAX? Do you get the increase in idle speed as well?

Of course, the ECU will up the idle, or at least open the throttle a little to maintain the idle speed, when the AC compressor kicks on, but I believe on MAX the compressor should be on continuously (not sure about this though). I'll SWAG that this is a 'loophole' in the throttle or other mapping that doesn't account for a large AC load on a hot day sitting at idle for a few minutes.

 

[831Bullitt]

Did you have the AC on MAX? Do you get the increase in idle speed as well?

Of course, the ECU will up the idle, or at least open the throttle a little to maintain the idle speed, when the AC compressor kicks on, but I believe on MAX the compressor should be on continuously (not sure about this though). I'll SWAG that this is a 'loophole' in the throttle or other mapping that doesn't account for a large AC load on a hot day sitting at idle for a few minutes.

I'm sure I had the AC up, though I don't normally run it on Max AC. I agree with you.

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