Corolla - Changing Spark Plugs

I have a 2003 Corolla with 127K Miles. I have not changed plugs so far. It runs and starts OK. I’m planning on changing the plugs. I’m told that the plugs and the ignition wires are different from the older model cars where you could pull the wires out easily and change the plugs one at a time. In this the plugs and wires are not visible. I presume they are under the engine cover. Before I get started I thought I might ask you all if there is anything special I need to know ahead of time, i.e regarding the ignition cables, plugs etc. I have the sockets and tools to do the job. Thanks for any pointers.

One thing of interest though that the engine idles at 2000 RPM when the engine is cold but settles down to around 900 RPM when it warms up. What could be causing it to idle high?

That’s a long time for plugs to remain in place on an aluminum head engine and your car should have COPs; which mean Coil On Plug. There are no plug wires to speak of.

When removing the COPs try to twist them back and forth a little while removing them. Hopefully the plugs will come out without damaging the threads. Stuck COPs and plugs is a reality when they’ve been in place for a long time.

Once out I would advise checking the spark plug gap and adjusting as necessary. Use anti-seize compound on the the threads of the new plugs and if the terminals inside of the plug boots on the COPs are not corroded dielectric grease should be used on both the inside and outside of the boots before reinstallation…

The high revving could be an Idle Air Control valve problem. A scan for codes may, or may not, show a code related to the IAC. Hope that helps.


Your idle situation is typical for many Toyota cars

I wouldn’t lose any sleep over it, unless your idle is also high when it’s warmed up

The idle speeds are normal for that car.

Regarding the plugs, there is one tool you’re missing; a manual to show you how to change the plugs. They are different from the old days. They have seperate coils on each plug mounted on top of a “pole” that’s directly conected to the plug. This setup is mounted and retained using hardware that routes and protects the wiring…which is thin, since it’s “primary” wiring rather than “secondary” (high voltage) wiring. I’ve found that if you don’t take the time to properly release the system that holds the COPs on these engine you can easily break the insulator ring around the top of the “pole”. In addition, it’s good to be aware that if you don’t disconnect the COP connectors properly you can break the retainers on the wires. You need to push the wiring connector IN before pressing the release tab. That releases the “hooks” in the conection.

None of this is rocket science. But I strongly recommend a manual. Or at least a copy of the Toyota repair procedure from the dealer’s parts guy.

I will defer on the Toyota idle issue. My cars rev up briefly when cold for a few seconds before idling back down to normal,
It just seems to me that idling at 2 grand until the engine is warmed up is a bit much.

I respect your opinion so want to see if you can clarify this for me.
I have bought Denso OEM plugs for my '05 Camry. Both Denso and Toyota repair manual advise against using anti-seize. I guess there is a coating on the plug and also by using the anti-seize, there is risk of over-torquing and damaging the head.
Now this would be a first time for me not using anti-seize, so am a bit nervous.

Don’t mess with the idle speed until after you have changed the plugs. Those plugs are supposed to be changed every 30K miles so they are way overdue and likely now gapped out of spec. Other advice on taking out “old” plugs and dealing with COP’s are good pointers that I agree with.

Get the right plugs (I use the OEM plug) and a new air filter and then see what the cold idle is like. 2000 rpm is high but if it settles down in 20-30 seconds to 1200 and then is 900 when warmed up that might just be “normal” for this motor and not worth messing with. Idle adjustments are now computer controlled and shouldn’t be adjusted especially by an inexperienced mechanic.

Hmm. Looking at the 2003 Toyota Corolla scheduled maintenance guide (from the Toyota site), they did use Iridium plugs in 2003, and the first recommended change is at 120,000 miles.

I’m surprised, but it looks like the OP is OK at 120k. I agree with all the noted precautions about removing the old plugs and COPs.

Galant, as much as I greatly respect OK4450’s depth of o knowledge and experience (I’ve learned a great deal from him), you are correct about the antiseize. It’s not recommended for these plugs.

Denso is one of the approved OEM suppliers to Toytota. I agree with Uncle T about using the OEM plugs. You’ve made a good choice of plugs.

@n2b, were the valve clearances checked at ~60K miles?
In any case I would take the valve cover off too (get a new gasket!) and check the valves.

The anti-seize on the Iridium plug threads are not the issue. The issue is whether someone with 2 canned hams for hands is overtightening the plugs and stripping or pullng the threads.

Speaking for myself and most mechanics I know, we do not torque spark plugs. It’s done by feel.

Regarding spark plug torque specs, there are several issues with that.
One is the accuracy of what is usually a 1/2" drive torque wrench being used at low settings.
Another is the often wide range of specs given. One example given in an NGK publication I have is 7-15 Ft. Lbs. That’s a world of difference and akin to a hand grenade tolerance.

I might note that the use of feel is even recommended by many plug manufacturers who will state this on the packaging. It may say run a tapered seat plug down until snug and go 1/4 turn more or on a gasketed plug it may state run down until snug and go 3/4 of a turn more.

Toyota recommends torque values. If my memory serves, it’s 18-24 ft/lbs for this engine. Anti seize makes accurate torque values impossible, and can easily cause overtorquing and resultant thread damage. Thes plugs have a flat shoulder with a metal crush washer. Proper torquing properly seats the washer without damaging the threads.

There’s no question in my mind that anyone who’s installed countless plugs can easily do so by feel. And I myself changed countless plugs by feel for decades before becoming a torque wrench advocate. But the OP is a newbie. He has yet to develop the muscle memory.

For those new to the forum OK4450 and I have been debating this “torque wrench or no torque wrench” question for years. I have only the utmost respect for OK4450 and there is nobody on earth to whom I’d rather trust my engine. However on this question we’ve developed different perspectives. It has long been my belief that two intelligent people with the same set of facts can draw entirely different conclusions, and I think this is an example of that.

If it has been that long and you are unsure how to do it your self, take it to an experienced mechanic. I would not want to follow the " swallow the fly " scenario and look at another problem I might create. Btw, I agree with ok4450. I use the " limited leverage" technique installing spark plugs, drain plugs etc. That is, I only use what torque I can easily generate with my wrist and forearm below my elbow.

I have no problem with varying opinions but there’s no way on Earth I would apply 20 or more Ft. Lbs. of torque to threads in an aluminum cylinder head; even if the threads are not even mildly damaged due to thread galling or pulling.

We also disagree on the manufacturing tolerance issue too…

Considering .0025 an “acceptable deviation” as per a bearing manufacturer is something I will never buy into in a thousand lifetimes; and new cars are being assembled with those parts. :slight_smile:

Definitely not with anti seize on the threads…

We do disagree on the manufacturing issue. 23 years in manufacturing as an engineer and quality engineer during the days when these new manufacturing principles were being introduced in this country, and having worked with and experienced these changes during that period, has defintely left me with a different perspective on tolerances than an engine rebuilder would have. When rebuilding an engine one works with tolerances. When manufacturing an engine one works with variation. The former will get you a good engine. The latter will get you 100,000 good engines.

I can’t recall what discussion the .0025 came from, but as regards bearings I’m still mad at the EPA…


“a 1/2” drive torque wrench being used at low settings"

Perhaps you misspoke?

Everyone I know uses a 3/8" torque wrench for spark plugs

A 1/2" torque wrench is massive overkill, I would think

FWIW . . . If there is a torque range, I go middle of the road

No, I did not misspeak about the 1/2" torque wrench. The few times I’ve used a torque wrench I’ve used a 3/8 or even a 1/4 drive. The 1/2 comment is based on watching others use the overkill method; not me.

The spark plug manufacturers all pretty much state that hand tightening is fine and that’s the way I do it. It allows me to feel the threads so to speak.
There’s also the issue of installing and torquing spark plugs on an engine where someone may have rammed them home before. I’ve been in the middle of a few of those, along with pulled cam bearing cap threads, and it makes me a bit gunshy.

@thesamemountainbike, the .00251 actually, was the tolerance quoted to me by Federal Mogul technical people after consulting their engineering drawings on a set of main bearings that measured all over the road map. That also includes the 3 followup sets that were ordered.
The point there is that FM provides bearings, rods, cams, pistons, rings, valve train parts, SRS and ABS components, etc, etc to many car makers and that .00251 hardly constitutes precision in my book.
If there was another zero tucked in between the two that are there, then I would agree.

It baffles me how someone would set oil clearance on a crankshaft journal when one half of a bearing shell is .0015 thicker than it’s mate for the other side.

Thanks to all of you for your insight into the layout of the plugs and the (new for me) method of attaching the ignition coils. This has been most helpful. I will do as one of you suggested and take it to a shop and have them change the plugs. You are right I don’t want to add to the problems with the possibilities of damaging the coil connector, etc. The added cost at the shop will be minimum anyway.

The multi faceted discussion on whether to use an anti seize on the plugs and whether to use a torque wrench to tighten the plugs was interesting. I used to be an aircraft engine mechanic from the time when all aircraft had piston engines. We always used just a spot of graphite grease very sparingly on the last three threads and never used a torque wrench. Just a little snug after the plug was seated was all that was required to make a good seal. The heat from the engine did the rest.
Thank you all again for your feed back

For what it’s worth, I’m an ex-aircraft mechanic also and plug installation was handled the same way as you describe.

OK4450, I’m actually surprized that the sleeve halves weren’t matched. I too am baffled by the belief that one could successfullly use sleeve halves of differences as large as .0015. There’s a lot to be said for sleeves being manufactured in sets.

I’m an old B52 guy, but my specialty was avionics. Never did any mechanical stuff. I spent my days on the flightline and in hangers.