I have a 2002 Toyota Prius with 120k miles and I don't think the spark plugs have ever been changed. Which spark plug type should I use? In the owner's manual it says " use only iridium-tipped spark plugs and do not adjust gaps for engine performance and smooth drivability." Does that mean I don't have to adjust the gap to stock specfications? Also, which socket should I use? There are 5/8", 13/16", etc with 3/4" drive. thanks.
You want to use only irridium tipped spark plugs. (I recommend the Denso plugs OEM replacement) When they say do not adjust the gaps, that means don't adjust them outside of specs. You definitely want to check the gap before installing to ensure the gap is set correctly. The socket you want is the small(er) spark plug socket (5/8) and, they should be set to the proper torque (so a torque wrench should be used). You will also need a short extension.
Also, I checked the voltage on the 12v battery while it was connected with car off and it was 12.1v. I read somewhere it should be 12.6v. is that right? thanks.
Yes, 12.1V is pretty low if the battery has no load on it. If the battery is reasonably new then you might try charging it overnight. If the battery is more than 4 years old you may want to just replace it now so that you don't have to worry about a future no-start issue.
The spec is 1.0 to 1.1 mm. I suggest you set the gap of the new spark plug at 1.0 mm. Do not adjust used iridium spark plugs as the ground terminal may snap off after the used plug is reinstalled.
I just got our 2008 Prius touring model back from the dealer after having plugs changed...we have 96k miles. The car was getting poor mileage before we took it in (~43mpg) but now it idles rough and seems to miss after starting. It is in a 40 degree garage and the rough idle and missing seem to dissipate after 5 minutes. On the road the mileage just dropped about 3-4 mpg using the same tank of gas and about same weather conditions. I plan to take it back. Should I ask them if they have the correct gaps, or if they used iridium plugs, or if they didn't connect a vacuum hose or something? I figure they are going to charge me again and just think it is another unsubstantiated complaint about mileage. Suggestions? I don't think I am imagining the rough idle or an abrupt drop in mileage.
Since the problem goes away after five minutes, I don't think a workmanship problem is the issue. Unless you can demonstrate the problem to the service writer, you may want to live with the issue for now. Otherwise, as you said, you'll be charged for another service visit and told "no trouble found". If you can demonstrate the problem, then maybe the tech will be motivated to find a problem with the system that increases engine idle speed and enriches fuel/air mixture under engine warmup conditions.
Advance Auto sells Denso Plugs Part 3324 for $9 each, check your FLAPS. Identical to the Toyota dealer plugs, just not in a Toyota box. They are pre-gapped just plug and play. Denso SK16R11 Iridium Long Life Spark Plug
Thank you Patrick. I'll keep checking to see what happens after startup. My wife drives the car most. I appreciate the feedback. T
Thank you for helping people. I am new gen 1 Prius owner and found so many useful info posted or just replied by you. Many thanks
You can download the Owner's Manual at Toyota Tech Info (Google that name), in the Manuals section, and it will have info like that as well (quick way to find in the Manual is to search for "denso"). Here's a direct link, for 2001 Prius Owner's Manual: https://techinfo.toyota.com/techInfoPortal/resources/jsp/siviewer/index.jsp?href=om-s/OM47401U/xhtml/OM47401U.html&locale=en&openSource=TechinfoPrelogin Screen grab from page 241: As mentioned above, the plugs typically come with the correct gap, but it doesn't hurt to check them. If they're off, I'd be inclined to return them, they might have been dropped or something. Use a spark plug wire gap checker, or that circular ramp style.
