A Toyota Tacoma owner is searching for answers after noticing some quite unusual behavior from their truck shortly after having its spark plugs replaced.
The owner shared the issue and their concerns on the r/MechanicAdvice subreddit, explaining that the vehicle is a 2021 V6 Toyota Tacoma. They took the vehicle in for routine maintenance, during which the spark plugs were replaced.
They then explained that after the maintenance, the truck appeared to act as if it wanted to accelerate while parked, and the owner had also noticed that the headlights seemed to be flickering.
With maintenance having just been completed on the vehicle, the owner was left wondering whether something went wrong during the service or if the truck just needed time to adjust.
Commenters Offer Some Advice
One commenter who said they worked at a repair shop suggested that a defective spark plug could be the culprit. They explained that they had recently replaced spark plugs in several vehicles and found that almost all of them had at least one defective NGK iridium plug that caused an engine misfire.
The comment went on to say that the vehicles experienced problems despite the new plugs not triggering a check engine light. After replacing the plugs again, the issues went away.
The owner responded that they thought this might be the issue, as they were worried the mechanics might have installed something incorrectly. They thanked the commenter and said they would reach back out to the shop to see about having the plugs replaced again.
How Can a New Plug Cause Problems?
Another commenter replied and asked the mechanic how to identify a defective plug. They also admitted that the discussion instilled further fear into them about performing a tune-up on their own vehicle.
The mechanic explained that a vehicle running poorly after a spark plug replacement could indicate a misfire. They suggested using a scan tool with live data to identify which cylinder was misfiring.
If the plugs had just been replaced and the problem began afterward, the mechanic said they would consider replacing the plug in the affected cylinder with a new one. However, they noted that other issues, including a faulty ignition coil, could also cause misfires.
They also explained that misfires can cut engine power and contribute to issues that cause headlights to flicker, as the Tacoma owner was experiencing.
Since the Tacoma owner noticed the issue almost immediately after having the plugs replaced, returning to the repair shop should be their next step, as suggested by the mechanic. There have been no further updates to the post about whether the problem was fixed.