Rough Idle, Random Misfire (Solved)

This is a general info post. I am making it in hopes that it may save somebody some time if they encounter a similar issue.

I recently had my spark plugs changed as part of Toyota's recommended service based on mileage. The service was completed by an independent garage that was not affiliated with Toyota. After the service was completed everything seemed fine. However, after a couple hundred miles I noticed rough idle. The rough idle persisted with the engine revved between 500RPM and 2500RPM with no load. Also, my fuel economy went from my typical 17.5MPG to no better than 13.5MPG. The truck did not display a CEL, but it did throw a P0300 (random or multiple cylinder misfire) code when checked with my code reader. I was driving across the country for work, so I was unable to return the truck to the garage that performed the service.

When I arrived at my destination I dropped the truck off with a small garage and they verified the misfire (both the code, and IRL). They also pulled a throttle position sensor code. I was referred to Toyota to handle the TPS issue as the small garage would be unable to program a new TPS to the truck.

The service department at Toyota was unable to verify the TPS code, so they began looking elsewhere. They pulled a spark plug to inspect and found that the new plugs were Autolite brand, and not Toyota's recommended Denso Iridium. They claim to have seen the same issue with other trucks after the spark plugs were replaced with anything other than genuine Toyota plugs. So, I had them change the plugs for me.

Within 20 miles after the Toyota service was complete the I noticed that the fuel economy returned to where I expect it to be. After ~300 miles the rough idle has not returned. So far, so good. I am reasonably certain that they correctly diagnosed and remedied my issue.

Note that even with the "wrong" spark plugs, cylinder misfires, and poor fuel economy I did not feel any apparent loss of power. The truck drove like normal, save for poor gas mileage and rough idling.

When I searched for potential solutions/diagnosis I didn't find any results that would suggest that installing spark plugs other than genuine Toyota replacements would cause an issue.

 

Wow, you must have paid a bundle for this?

What did the first garage charge you for the plug change, and what did Toyota charge you for doing the same again?

I just watched a video on a plug change on a 2016 TRD Off Road. Made me shake my head in disbelief. Guy said about 30 minutes for the passenger side, and about 2 hours for the driver side plugs. A lot of hoses and connectors to remove before you can even visually get access to the plugs.

Another guy commented his dealer wanted $700 to change the plugs on his 2017 Tacoma....

Anyone have some feedback on what they are being charged by the dealer to change out the plugs on a 3rd gen Tacoma?

I have changed the plugs on a 1965 Pontiac, a 1970 Pontiac Firebird Formula 400, a 1986 Ford F150, a 1994 Mazda B4000, a 1996 Ford F250, and a few more cars. Plus on my own done all the brakes, radiators, starter motors, alternators, belt changes, oil changes, tune-ups with plugs, points, condenser, set timing, etc. A whole lot more besides, and I am not mechanically trained, just DIY for 45 years now.

The longest it ever took to change the plugs, either 6 or 8 depending on V6 or V8, was a grand total of 20 minutes if was 8 plugs. That's if I fell asleep half way through the process. On none of those vehicles was it necessary to remove anything to get at the plugs. Just lean in, socket wrench them out and new ones in. Normally about 2 minutes per plug.

Hey, I like my Tacoma, but man these newer vehicles are over designed and over built. For those too young to have not worked on some older vehicles where all you needed were a socket wrench and a case of beer, it is pretty unfortunate this is how it is now.

 

Trd Offroad and pro have a huge electronic master cyl. It makes it hard. Took me about 2 hours total.

 

There's a good DIY thread on here ref changing the plugs on the 3rd gen V6, includes pics, tools required and tips/tricks.
No way the passenger side takes 30 minutes, it's easy (although not as easy as the V8s of yesteryear lol).
The driver's side is a bit of a bugger, but again not REALLY bad. Some of the stuff that was suggested in the DIY thread wasn't even necessary to get at them.
Edit: I have a Sport, so no huge brake booster thingamajig on the driver's side to add to the fun.

 

I'm agree with you, the good old days I guess, I use to have fun working on my truck but now it's kinda pain ass.

 

This whole ordeal cost more than I am comfortable sharing. The Toyota parts an labor definitely cost more than the independent garage.

I plan on contacting the garage that put the wrong plugs in and trying to come to some agreement to recoup some of my losses. They done fine work for me until this point, and I'd like to maintain a good relationship with them if at all possible.

 

Most businesses will try to take care of a customer especially a repeat customer.
That being said those Autolite plugs cost a 1/3 of most plugs and there is a reason for that. I wouldn't put Autolites in a mower.
A dealership will just about always cost more but you are getting a trained technician and top shelf parts.

 

While doing research, for just about any Japanese vehicle, for spark plugs you will find buy Denso or NGK only.

 

Had this recently at my dealer, autolites caused huge issues and customer still blamed me, even though I never installed the bastards.

 

Yup, here is a typical Ford straight 6 from the old days, plugs and distributor cap just sitting there, lots of room, no complications. The 300 6 cylinder like I had in my 1986 F150. The 300 straight 6 was indestructible, 500,000 miles on them was nothing.

That truck had crawl control too, but better….

Granny gears so low, that even with my 4 spd manual I could put it in 4-lo first gear, let the clutch out and walk beside it up or downhill. Great for when stuck in the mud and using my come along to get me out. Leave it in first, and crank that rachet and when unstuck just hop in as it is barely moving.

4-lo first gear in my TRD OR is just too fast, still have to use the brakes on steep rough downhill.

Not sure how we got to this stage of trucks beingso fancy, and so complicated. Seems backwards.

 

Well, it's a little late now, but this is a sticky thread about general maintenance and will help you in the future at least:

General Maintenance Thread

Just FYI, next time you take it to the shop to have anything done or they recommend any work to be done, do the research. Get a print out with part numbers, take it home and look everything up. Call around and get second opinions and prices. You'd be surprised at how many shops you have to specify everything or they will not do it right. Just trying to keep it simple for you in the explanation, but basically have a plan before you go in and know what to expect. Write prices down for parts you already know... Like spark plugs. That way you can judge the markups and labor fees.

I'm willing to bet that shop didn't do their research and they use the same plugs across the board because they rarely do certain vehicles. Specialty shops are always a good start if you are lucky enough to live near one... Like one that works on Toyotas, Lexus', etc etc...