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Rough Idle, now Check Engine light on?

Tiny
TUBEGEEK
  • MEMBER
  • 2010 FORD FUSION
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 117,000 MILES
Car listed above is an SE model with 6F35 six speed transmission.

Not driven that much on a regular basis; one 20-mile round trip some weeks, maybe once a month a 200-mile trip. Otherwise, short hop city driving.

About 2 or 3 months ago I started noticing rough idle from time to time. Not seeing a pattern hot or cold. From time to time a little "bump" feeling when stopped - like the clutch engages slightly for an instant then not?

About a month ago horrible misfiring, bucking bronco, from a cold start. No check engine light this time. Drove to the mechanic, changed spark plugs did not fix. Changed ignition coils, which cured the bad misfiring, seemed to be running fine. Past few weeks, intermittently getting the slightly rough idle and occasional "bump" again. More often/worse than before.

By comparison with most cars this car probably gets driven on short hops more often than most. Sometimes it just barely gets a chance to warm up or even doesn't get to. Stuff like taking a one-mile ride, parking, riding back hours later. Or a few times around the block to switch parking spots. But there is no real difference between the idle behavior when cold and on the occasions when it does get a chance to warm up properly.

I don't notice any correlation between really cold days and warmer days either.

No weird noises so far as I can tell.

I don't necessarily think the bad misfire problem was related because the behavior is still pretty similar to before that episode. It's hard to say because it's not consistent, sometimes doesn't occur, sometimes doesn't for a while, does for a while, doesn't again.

Today: 30-mile round trip, started with stop and go city driving, then some speed-limit highway, then back again.

During the initial stop and go, check engine light came on and stayed on for the whole 60 miles. I did get to high revs for very short stretches a few times. Car runs fine once up to a few MPH, still rough idle and bumpy/jerky when stopped.

I had ordered a Bluetooth OBD2 dongle already, coming in a couple more days. Will update this question with codes as soon as I can.

When I think about the couple of long road trips this summer, I don't recall any rough idling at all. The start of it was this fall during the pattern of getting less use, but I first noticed it right after my daughter dropped it off here - so after her 100-mile highway trip. I remember I wondered if she got a watered-down gas fill up somewhere, it was when the gas prices were jacked up. It got somewhat better for a while, still intermittent, then the misfiring/plugs & coil incident, now the several weeks of intermittent rough idle and "bump"ing.


Advice from @galopigos on reddit (condensed):

Okay short hops and not running much can cause build up in the cylinders because the carbon doesn't get burnt out of it much.

So, connect the scan tool and find the long term and short-term fuel trims and write down what they are at idle, if you can find the MAP and MAF numbers grab those as well. Next, take it out on the highway and run it as hard as conditions allow, you want to get the engine really warmed up and work it some. That way you will be able to see if it's just the short hops letting things in the cylinders get dirty.
Now as soon as you get back from that run throw the scan tool on it and see look at those same trims and numbers.


Now if the idle improves after the run it's likely just the short trips. Have you seen any coolant loss?.

No coolant loss as far as I can tell. Will double check that.
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Tuesday, December 27th, 2022 AT 6:23 PM

62 Replies

Tiny
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Just adding one other detail I have noticed, the temperature gauge is always at about 1/3, so, a little colder than centered.
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Tuesday, December 27th, 2022 AT 7:18 PM
Tiny
STEVE W.
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Okay, with the temperature gauge it's possible the engine coolant temperature sensor is faulty if it just stays there. If the ECU thinks the engine is running cold, it will change the fuel mix to help it warm up faster and that could cause a rough idle. The codes you pull may show more information, so we will wait for those before jumping the gun too far. Please keep us in the loop.
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Tuesday, December 27th, 2022 AT 8:42 PM
Tiny
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Will do. Dongle arrives in two days according to the package tracking, hopefully no flash blizzards between me and that truck.
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Wednesday, December 28th, 2022 AT 2:02 AM
Tiny
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Dongle arrived. A little flaky connecting to the OBD2 port under the dash but eventually I got it to stay on steadily.

Here's what I found using live data from the free version of the Piston phone app.
First number is idling, 3 or 4 minutes after start up. Figures that are in brackets [] are taken revving to about 2500 RPM. Most did not change, so no brackets. Screen shots are below, the newest one on the left was after the shutdown/restart.

Coolant temp: 171 [163]
Short term Fuel Trim Bank 1: varied between -5.5 and +3.9 [similar when revving]
Long Term Fuel Trim Bank 1: -3.1
MAF Air Flow Rate: 0.4 to 0.5 [higher when revving, 1.5 to 2.5]
O2 Sensor Voltage bank 1 sensor 2 : 0.8 with small variations
Short Term Fuel Trim Bank 1 Sensor 2: 99.2

In addition I had a code P303, Cylinder 3 misfire, which was there twice (one was Permanent, the other was Current.)

I cleared that code, and CEL went out. "Permanent" code went away after a shutdown/startup cycle. Did not come back so far.

During this testing the car was NOT idling rough at all, so I guess this is baseline info. Only a few minutes of running in all.

I see that STFT B1S2 at 99.2% is normal.

Coolant level was at the seam in the tank, so - I think - that's at the bottom of the COLD range, there is a mark about an inch above the seam which I think is the top of the range. This is what I remember from a previous check also, so not losing coolant so far as I can tell.

Next step, I'm guessing, is to drive a bit until I get the rough idle and check again while it's acting up?

Any tips to get the dongle to make solid contact instead of needing to be jiggled until it lights up steadily?

Picture of the ELM327 scanner here:

https://i.ebayimg.com/images/g/jSoAAOSwRLRie-Jj/s-l400.jpg
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Thursday, December 29th, 2022 AT 2:03 PM
Tiny
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Second session:

After some intermittent rough idling, and about 2 solid minutes of revving over 3000 RPM,
the only changes I see from the scanner are occasional dips in O2 Sensor Voltage bank 1 sensor 2 : it would go as low as.12 for short periods which seemed to coincide with rough idling, and also the Long-Term Fuel Trim Bank 1 was changing more than it had before, with dips to -2.1 and then returning to a steady -3.1.

Everything else seemed about the same.

Idling was on the lesser side of the roughness spectrum this run, it was intermittently a lot rougher yesterday when the CEL lit up.
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Thursday, December 29th, 2022 AT 3:05 PM
Tiny
STEVE W.
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Okay, the P0303 code is pointing at a misfire, Fords in that era didn't trip the code until there was a long period of misfires. Check to see if that app can read the misfire monitors, it might let you watch the cylinders to see if it's missing during the rough idle. I would also take it for a drive and see if the coolant gets up to a hotter temperature, which should have a 185 thermostat in it. The fuel trims look good once it warms up.
If you want to do a bit of testing, pull the coil off 3 and swap it with 1. Then swap the 3 plug with 4. See if the misfire code travels with one of the parts and you will have found the bad part. I would say to change the plugs as they are due at 115,000, if you already did and it started missing after that it could be a bad plug or a failing coil. The swapping could pinpoint it if the misfire shows up during the rough idle.
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Thursday, December 29th, 2022 AT 5:25 PM
Tiny
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Plugs and coils were replaced just a couple of weeks/less than 200 miles back, during the "bucking bronco" horrible misfire episode. (I know that first post was kind of rambling.)

So, would it be a good idea to take it back to the garage that just replaced plugs and coils? They'd probably stand behind the new parts, at least I'd hope so. And if I go poking around in that spot that probably wouldn't fly anymore. I can tell them I tried to diagnose it myself but pulled out before I started messing with their work and it'd still be true at this point.

Couldn't hurt to get the upgrade to Piston I suppose to watch the live data better - hopefully including the misfire info.

I was really hoping for "clean/replace the MAF sensor" or something really stupid/easy/cheap like that.

Thanks for your advice. What do you think of my "go back" idea? I feel like it's reasonable under the circumstances.

Is there anything that might be murdering plugs or coils?

Temp: I can at least tell you that the gauge never got to the center of the scale during my 30 mi up/30 mi back trip on Tuesday.
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Thursday, December 29th, 2022 AT 6:49 PM
Tiny
STEVE W.
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So, it was missing badly, and you took it in and they did the plugs and coils, did it run better and then started this? You could take it back and tell them that it still has a problem but they might say "Well it could be your injectors not the parts we installed" I would swap the parts around and see if it changes, you can easily swap them back if nothing changes, or swap them once you determine that say the plug is misfiring. Then see if they stand behind their work. The usual killer of plugs and coils is more physical damage. Like a cracked plug or a coil that has carbon tracking. Another variable is the parts they used. Some vehicles are really fussy about the parts. I've seen Chryslers with the 3.7 and 4.7 that were running really good and the owner or another shop changed the plugs from the common copper plugs they run over to double platinum plugs because they were "best" and they start running like poo, misfires and issues galore, change back to the base plugs and everything is cured.
Look at what they used and see if it was OE or at least something other than Dorman.
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Thursday, December 29th, 2022 AT 7:02 PM
Tiny
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Okay. Makes sense. Will I be able to ID the plugs without removing them? I don't think I have a socket deep enough to pull the plug, of course I can get one if necessary.
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Thursday, December 29th, 2022 AT 8:54 PM
Tiny
STEVE W.
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You would need a plug socket and extension to get to them. Sounds like a good reason to get a tool kit or at least get the tools you need. Something like this one would work. https://www.harborfreight.com/hand-tools/tool-sets/mechanics-tool-set-225-piece-62664.html Or https://www.lowes.com/pd/Kobalt-243-Piece-Standard-SAE-and-Metric-Combination-Polished-Chrome-Mechanics-Tool-Set-1-4-in-3-8-in/5001996843 There are multiple places you can get kits like that. Just pick one that is from a local store and has a decent warranty. Both of those are lifetime. That way you also can deal with other repairs.
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Thursday, December 29th, 2022 AT 9:11 PM
Tiny
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Some new observations. (I haven't done any swapping yet.)

First: rough idling never seems to happen right away when the car is ice cold.

Second: I'm now seeing the car come up properly to normal warm during a couple of brief city drives, about a half an hour. OBD2 says temp is about 200° when warmed up. Gauge is about in the middle.

Third: when I'm stopped at a light and start to feel vibrations/jerks, shifting to neutral makes the roughness go away. I only feel the roughness when in gear and stopped.

I had not had this happen back before the plugs and coils were swapped. At that time, rough idling would not go away if I went into neutral, I did test it back then.

I had not tested this out again after the plugs and coils were replaced, not until the last couple of days. Now: shifting into neutral immediately results in smooth idling, no jerking.

I often say when trying to fix stuff "there's no law that says you don't have two problems." I think I may have started with two separate problems - one which got worse and then was fixed by the plugs and coils being replaced, and another which now seems to me to possibly involve the driveline/transmission.

My inclination is to go ahead and carry out the transmission fluid drain and fill I was about to do - I have what I need to do it. I held off because I didn't want to confuse the issues, but I'm thinking it may be worth a try now if the trouble I'm still having does relate to the clutch and transmission. Worst case I'm wrong and I've done a recommended service but gotten no improvement to my problem. Best case there is an improvement after swapping out the old transmission fluid.

I can always start coil swapping next if the fluid replacement does no good.

Good idea? Bad idea?
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Sunday, January 1st, 2023 AT 7:59 PM
Tiny
STEVE W.
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At least you have a plan. Plus, as you said it's a service it needs anyway. If I'm understanding this you had a rough idle before that didn't stop in neutral, then you swapped the coils and plugs and now it still has the rough idle but only when in gear which would be under a load and would exacerbate any faults because it's at idle and not producing a lot of power.
Really nothing to lose to service the transmission.
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Monday, January 2nd, 2023 AT 6:31 AM
Tiny
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You've got it straight. At least it's my interpretation of the current state of affairs.

Okay, up the ramps I go!

Happy New Year. Thanks for the help. More on this once I get a chance to do the job and test the outcome.
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Monday, January 2nd, 2023 AT 8:00 AM
Tiny
STEVE W.
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Okay, another test for you when you get off the ramps. Get a can of carb cleaner you want the stuff that says that it's so flammable it will blot out the sun, not the enviro-friendly version you can wash penguins with. Now on a cold engine, start it and take the can and spray around the intake manifold, any vacuum hoses and around things like the throttle body. Listen for the engine rpm to change or make odd noises. Look at the area you just sprayed. At idle under load the engine is producing a lot of vacuum, a small vacuum leak could also cause the rough idle and misfires. You might also notice misfires if you were coming downhill and let off the throttle and let the engine pull even more vacuum. Those can be harder to feel though.
Oh, be careful letting neighbors see you with ramps and tools, you may suddenly be tagged as "the one who fixes cars", lol.
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Monday, January 2nd, 2023 AT 11:16 PM
Tiny
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LOL - I think their risk would be far greater than mine in that scenario!

Thank you. Probably not today - raining. Hopefully this week though.

Hopefully the penguins will get their rinse from the clouds this time - they get pretty smelly.
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Tuesday, January 3rd, 2023 AT 11:16 AM
Tiny
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Okay, I put mine up on the ramps today, just got finished. I have not yet done my ride-around, so I am not confident in my final fluid level yet, I'll do that in the next day or so.

While running the engine before and after I again saw Cylinder 3 Misfire codes. Too soon to evaluate overall jerkiness and idling - I'll be taking an evaluation ride soon. I cleared the codes.

While up on the ramps and cold, a little less than 4 quarts of ATF drained out. I measured what came out and refilled it twice with the same amount, so I still have about 2 quarts on hand in case the level needs topping up once I do the correct process of checking on level ground, after riding around, shifting, etc. I used Motorcraft Mercon LV, I bought 2 Ã 5-quart jugs on Amazon - my local AutoZone did not have it.

The seam down the middle of the transmission did have a minor amount of oily dirt stuck to it and the belly cover also had a small amount of greasy dirt accumulated in its low spots. I'm thinking that 117,000 miles probably just looks like that, but I'll keep an eye on it.

The old fluid was opaque, brown, but not obviously gritty, and it looked about the same both times I released it. This is what I've been told to expect from ancient Mercon LV

My belly cover appears to be missing two pieces - a roughly 5-inch diameter round snap-in piece that I think is for draining the cover before you try to remove it, and a rectangular piece (supposedly) attached by screws that go into clips in the cover. That one looks like it's for service access to the bottom of the engine and radiator towards the front of the car. I guess I'll have to try and retrace the car's last 50 or 60,000 miles and see if they're still by the side of the road where they fell off.

Feeling pretty good - my first time ever doing my own maintenance, and now I have the ramps if I want to do my own oil changes or whatever. Old dog learns new trick: alert the media!
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Wednesday, January 4th, 2023 AT 1:07 PM
Tiny
STEVE W.
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Yes, it's common to see seepage on an older vehicle, what you don't want is dripping or worse a steady stream. Fluid sounds normal for the vintage. Access covers and plugs are a common loss, the round one is a rubber plug, I've seen them fall out when they were taking new ones off the trailer! They generally make the covers and then decide "Oh we need access here for the oil filter" They put the hole in, then a month later stop using the engine that hole works with!
Sounds like you have a hunt if it's only cylinder 3. P0303 code. When it gets nicer you can swap some parts around and see if it is a cheap part. I've been running into a lot of junk right out of the box in the past year. I think the factories are telling the QC folks to take vacations and letting the customer be the Guinee pigs, like the software folks do...
Seems like you have a handle on things and more important are willing to learn as you need to, that is something that can be rare in the DIY realm, everyone wants to watch a video and instantly have the answer, which works for some things but for vehicles it can be interesting...
If you want to learn more about testing and what things you see on the scan info you can hit a few YouTube channels ScannerDanner, deadondiagnostics5502, Diagnosedan, PineHollowAutoDiagnostics and SouthMainAuto. Just don't be shocked if you start questioning everything the shop does....

This video might point at yours in terms of testing coils: https://www.youtube.com/watch?v=s8B6jAq6RnU
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Wednesday, January 4th, 2023 AT 6:04 PM
Tiny
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Steve W, thanks for the videos, those guys were fun to watch, kind of goofy. I saw the FordTechMakaluko video on spark plug replacement also which shows my exact engine and its coils etc.

I have a good feeling about my local shop honestly. I think I'll do the swap, see what happens, and if it follows the coil that he just put in I'll talk to the guy and all I really would ask him to do is hand me a new coil. The swap to a new coil is just the one bolt and the one clip, I'm just as happy to do that so my wife can think I'm a hero if I end up fixing it.

If I don't, well, you've given me a couple more ideas.

Thanks for the encouragement. I'm not super afraid to dive in and try to work on pretty much anything. Being a homeowner, you get pretty used to breaking stuff with a cat's paw and patching it back up, you get desensitized to the disasters. The hardest part honestly is I have no good place to work. I did this fluid swap in just a bigger-than-usual parking spot out on the street, ramps and all.
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Wednesday, January 4th, 2023 AT 6:51 PM
Tiny
STEVE W.
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Brian also has BSG Automotive as his shop and a YouTube channel as well. Paul Danner, Ivan at Pine Hollow, Eric O are all folks I've went to training with or met over the years. All great folks. I started out under a tree on the lawn.
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Thursday, January 5th, 2023 AT 12:24 AM
Tiny
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Swapped coils. Misfire followed the coil on the scanner. I spoke to my mechanic; he's going to put a new replacement in for me tomorrow. He had tossed the originals, and two of them were certainly bad so trying to test with one of them would have been a crapshoot anyway.

The 4 coils now in there are bright shiny and new, so I guess a new-part failure. In the tube world, "infant mortality."

Or a second problem will show up once all the coils are straight. Fingers crossed. Thanks for the backup!
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Thursday, January 5th, 2023 AT 2:31 PM

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