I have a 2017 VW Jetta manual 5 speed with 42K miles. I recently changed the spark plugs and the car still has a small random knock, usually in 3rd gear at about 30 mph. VW can't confirm correct gap, but I checked them before installing them. They are about (.025?). The knock has gotten much better since changing them. I heard coils could be the culprit. How do I check for that, and what else could I look for?
Well, if your engine was misfiring, you would get a check engine light. Does the engine knock when at that rpm while sitting, or in other gears? I would be strange to get an engine problem only at one speed, only in one gear.
I haven't heard it knock at idle, or when in faster acceleration.
The knock was more pronounced before changing the plugs (at 41k miles). It's only been noticeable with reverb from close low items, such as curbs. It does appear to be most common in 3rd and about 30mph, while doing slow-ish acceleration.
After reading the replies, I have tried listening more and driving differently. The knock is still audible in the 20-35 range, regardless of gear. I also heard it today at about 45. I can also hear it when accelerating faster. Hoping this gives better detail for more suggestions.
Are you using the correct grade of fuel which your owner’s manual recommends?
Yes. The user manual doesn't require anything above base unleaded (87?).