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.
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.
Dec 27, 2022 at 6:23 PM
