Hi everyone, I need some advice regarding a problem with my 2019 Toyota Prius (75k miles). Recently, during a full service, I replaced the spark plugs for the first time. Before this, I had done several services but hadn’t changed the spark plugs. My combined MPG used to be around 67, but after changing the spark plugs, it dropped significantly to about 55 MPG. There’s no error on the dashboard, but I’ve noticed something unusual. When accelerating sharply at speeds of 20-30 mph, the car feels a bit shaky, like it’s producing less power. I checked the spark plugs, and they’re fine—they were purchased from a Toyota dealership. However, I did notice that when the mechanic was replacing the spark plugs, he struggled a bit to put the connectors back in and removed a small red rubber piece from the connectors. I’m wondering if this could be causing an issue, possibly leading to a misfire in one of the cylinders. I’m completely clueless at this point. Could the connector issue be the root cause, or could something else be wrong? Any advice from the experts here would be greatly appreciated. Thanks in advance!
unless the uk is different, plugs should not be replaced until 120k. when replacing plugs, only buy them from a dealer. most everything else are chinese counterfeit
You may just have a bad tank of petro. Dump some CAT safe, octane boost, injection cleaner in your gas tank. If the problem still persist on the next tank of petro, take it to another shop and tell them your concerns. Previous mechanic could've cross-threaded one of the new plugs, causing a compression leak in that cylinder. You can usually see the blow-by, just simply looking down the spark plug well. Hope this helps and it's just a bad tank of petro.....
When getting work done I typically ask for the old parts that were removed / replaced back. It's only helpful if the old parts can help you understand how they were removed or in your case, what those red parts of the ignition wire(s) the mechanic pulled off the wires. Starting off with the small parts like plugs, wires, suspension links, etc. can teach a lot about any car. Plus if like @bisco mentioned above, if the plugs he used were not OEM, you'd have the old OEM to put back in and see if that clears up the misfire for you. I don't know what the red part might be, I might be able to see more later if I pull my spark plug wires, or someone else knows what that red piece of the ignition wire might be.
was the mechanic that replaced them from a dealership or somewhere else? Not that it makes much of a difference these days, at least on this side of the pond.
