Corolla Misfire, Oil on Plug Threads

[Jimmy]

Hello ladies and gents,

New to the site but a HUGE fan of youtube videos from ETCG. Here’s my problem:

I have a 2000 Toyota Corolla LE, standard shift, 121,000 miles. About 2 weeks ago, all was fine as I was driving, but then noticed a sluggish response when I stepped on the pedal. The CEL started flashing for a minute, then stayed on steady. I went to autozone and had it checked with the OBD tester. It showed code P0304-misfire cylinder 4, along with an O2 sensor as a secondary code.

I bought and installed 4 new iridium plugs and reset the CEL and the car ran much better….for about a half day. The misfire started again but no CEL this time. Well, I figured that the coil packs should probably be replaced also, so I did this too. I replaced all 4. Started it up and the idle sounded strong…I thought this was the fix. Took the car for a 20-mile test drive and ran it hard. It ran GREAT!!!! At the end of the test drive, I pulled into my driveway and it started the misfire again, but not as bad as before.

I pulled the plugs and the threads were pretty darn wet with what I believe is oil. It didn’t smell like gas so I ruled that out. Before I start changing every part that I’ve seen that “COULD” cause a misfire, I figured I’d run it through this forum first.

A few other things that may or may not be important:

-the car kicks out a nice poof of smoke from the tailpipe during a misfire.
-misfire seems stronger after having gone down a steep hill, stopped at a stop sign, and then accelerating from the stop sign. (not while stopped at the sign, just after leaving the stop)
-when in neutral and at idle, when I push the pedal (or the throttle cable), it sounds like the engine takes a quick “Gasp” of air before the RPM increases.
-Still excellent fuel economy—36/gal combined on average (I edited this post to include this information, since you’ll see an entry mentioning this by me below)

I’ve seen things suggesting the IAC, MAF, PCV, etc. etc. I have not replaced or cleaned any of those yet. I guess I could, but I’m thinking something is going on right after replacing the plugs and wires. The car runs great immediately after the change, but then it goes back to its shenanigans.

Should there be oil anywhere on the plug? Or is it supposed to be on the threads? If not, should I replace the valve cover gasket that has the spark plug gaskets included?

I’m at a loss and I appreciated any and all suggestions. I’m trying to be a DIY mechanic like ETCG says we can all be (to an extent). I really, really want to fix this myself so I can say that I did it (with some help from here, of course)

Thanks in advance.

Topic

[Jimmy]

I forgot to add that I rented a compression tester and performed that also. The numbers were good both wet and dry. Not sure how important that is, but I really wanted to get my hands dirty with this.

[Its me]

What was your second code (the O2 code?)… I am wondering if you have a P0171…

I would start of with checking the fuel trims… See what we are dealing with.. A HF Scanner for $59.99 can do this…

To begin:

The MAFs in these things cause real issues… These are the #1 cause of the P0171 code in the 8th Gen Corolla… I recommend you at least clean yours….make sure you remove the MAF to clean it and that you clean the actual wires that are down in the MAF (Not just the exposed red bulb that is is the Intake Air Temperature sensor). Also, only use MAF cleaner, nothing else…. Also after cleaning the MAF, ensure you reset the computer (disconnect neg battery cable for around 3-5 min)…. Drive the car around at varying speeds for 30 mins to an hour so the car re-learns its fuel trims..

The oil on the plug is a bit of a concern if you are getting proper PSI from the cylinder compression test. Compression should be 150 to 212 PSI per cylinder with none being over 20% different than the other. The 1.8 liter engine does have known issues with oil burning…. The holes in the piston ring grooves are too small and get clogged unless the oil is changed regularly…. Is your engine an oil burner??(a quart or so a month)

I recommend you check your fuel injector harness (with noid light) and your fuel injectors. A bad fuel injector will cause a misfire code (have seen it). Sometimes the clips on the harness break and do not stay attached to the fuel injector properly (seen that). Sometimes the Fuel injectors are dirty or bad… Only replace fuel injectors with Densos. There is a seller on Ebay who sells new real Densos for your 8th Generation Corolla for around $130 for all four…

Another thing not to skip over is a clogged cat… Sometimes people put cheater extensions on the downstream O2 sensor so they will not constantly throw a P0420…. This car did have a serious issue with throwing a P0420 (catalytic converter efficiency problem) so people added them, now the car seriously can’t tell when it has a clogged/inefficient converter… Check to ensure there is not an extension on your downstream O2 sensor…. If so, remove it and see what happens.

I recommend only NGK plugs for this car… Toyotas can be real picky…. Do check the PCV… I also hear people say all the time about the IAC but truthfully, I have not seen it have that many issues on this make and engine….

Good luck,

-Karl

[Jimmy]

Unfortunately I didn’t write down the second code (for O2) so I’m not sure, and I can’t get the CEL to come on again.

I did get those good readings from the compression test as you mentioned. As for the oil consumption, the car normally burns about 1 qt/month, but lately it’s been burning about 1 qt/100-200 miles–a very, very noticeable difference.

One other thing I forgot to mention is that the fuel economy is still fantastic…I still average 36/gal combined. I’ve seen other threads where people are experiencing poor fuel economy. This is not the case with my car.

I will start with your suggestions and report back. Probably won’t get to it until tomorrow or the weekend.

Thank you for the response.

[Its me]

Let me be very frank with you. Your engine is not long for this world if it has the oil burning problem… The time is even closer since you say it has recently gotten worse.

If you are handy there is a DIY fix for it here…. http://www.toyotanation.com/forum/131-8th-generation-1998-2002/402362-diy-oil-consumption-fix.html

Also, these Corollas are pretty simple cars. They usually only throw about 5 consistent codes:

P0420 – Catalytic converter not working within specs
P0171 – Lean condition
P0172 – Rich Condition
P030X – Misfire in Cylinder X
P044X – Caused by EVAP leaks, bad VSV’s and most usually a charcoal canister that is flooded with gas by an owner who insists on filling the fuel tank after the pump handle has clicked off again and again…

Good luck and let me know what you find out…

[Jimmy]

Ok, didn’t get much done just yet….juggling too many things, but here’s what I did do:

Cleaned the MAF sensor with MAF cleaner as suggested. Also cleaned the throttle body and plate for the heckuvit. Test drove it, no change.

Replaced the PCV valve. Test drove it, seemed to run better, but still had a slight misfire on a couple of occasions but not nearly as bad as it has been. It seems to misfire much, much less, almost non-existent, but still shows up intermittently on acceleration in 2nd and 3rd gear.

There is no extension on the O2 sensor/cat, and the wires to the injectors are good. I unclipped the injectors each separately and caused the engine to run differently.

I disconnected the neg battery terminal after cleaning the MAF, and then again after replacing the PCV as you said so that the computer would relearn the fuel trims.

I guess I’m wondering why the car would run really well after initially changing the plugs, then it would go back to misfiring. Same question for when I changed the coil packs, or COP wires.

The other thing I’m wondering about is why the smoke comes out of the exhaust pipe after descending a steep hill. I have a really steep one near my house and it’s my test route after I fiddle with my attempts at fixing the car. It will kick out some smoke at other times when it misfires, but will ALWAYS kick out a large smoke cloud after leaving from a stopped position at the bottom of that steep hill.

Also, would a leaking injector cause worse gas mileage? Or no? I’m getting great gas mileage even with this misfire issue.

Thanks for the link, but if that needs done, I wouldn’t even attempt it. Best left to a pro.

[Its me]

[quote=”TonyTwoGloves” post=66861]Ok, didn’t get much done just yet….juggling too many things, but here’s what I did do:

Cleaned the MAF sensor with MAF cleaner as suggested. Also cleaned the throttle body and plate for the heckuvit. Test drove it, no change.

Replaced the PCV valve. Test drove it, seemed to run better, but still had a slight misfire on a couple of occasions but not nearly as bad as it has been. It seems to misfire much, much less, almost non-existent, but still shows up intermittently on acceleration in 2nd and 3rd gear.

There is no extension on the O2 sensor/cat, and the wires to the injectors are good. I unclipped the injectors each separately and caused the engine to run differently.

I disconnected the neg battery terminal after cleaning the MAF, and then again after replacing the PCV as you said so that the computer would relearn the fuel trims.

I guess I’m wondering why the car would run really well after initially changing the plugs, then it would go back to misfiring. Same question for when I changed the coil packs, or COP wires.

The other thing I’m wondering about is why the smoke comes out of the exhaust pipe after descending a steep hill. I have a really steep one near my house and it’s my test route after I fiddle with my attempts at fixing the car. It will kick out some smoke at other times when it misfires, but will ALWAYS kick out a large smoke cloud after leaving from a stopped position at the bottom of that steep hill.

Also, would a leaking injector cause worse gas mileage? Or no? I’m getting great gas mileage even with this misfire issue.

Thanks for the link, but if that needs done, I wouldn’t even attempt it. Best left to a pro.[/quote]

Sorry to hear that the suggestions did not improve performance that much… I do suspect that replacing the spark plugs would improve performance initially until they became oil soaked… And yes, a leaking injector would cause the car to get worse gas mileage….

As I have said before, this engine is in its death throes… The good thing is that 1.8 liter 1ZZ-FE engines are easy to get…. and they can be switched out in a day… I have done multiple engine swaps in this make/model of car and there is nothing really that hard (except getting the rear motor mount to line up)…. If you need assistance, let me know…. I will probably photograph and document the next one I pull for this site…

Good luck and all the best..

-Karl

[Geronimo Forbes]

Yes you should replace the valve cover gaskets.If you see oil on the coil/ wire boot, thats and indication the the valve cover is leaking. As you were removing the spark plug the oil may have got on the threads causing you to be confused. And yes, that can cause performance issues.

[Geronimo Forbes]

Sometimes a simple problem can generate a bunch of codes. Make you life easier by fixing the obvious first. Just my opinion.

[Daniel]

Bad piston rings, valve guide seals, or valve cover gasket could all cause oil on the threads of your spark-plugs. The problem is, it is very unlikely that any of these problems would cause oil on all the spark plugs at the same time. The most likely culprit for the oil issue happening on all the plugs at the same time would be a bad pcv valve. Pcv valves typically only cost a few dollars so (to resolve the oil issue)this would be a good place to begin.

[Mark]

the valve cover is likely leaking internally. There are seals around the spark plugs holes (I forgot what they are called for sure) but when you pull the cover off you will see them and you should replace those along with the actual valve cover gasket. I think if you got good compression test on it then its probably not piston rings or a burnt valve. My 2 cents.

[Jimmy]

Agreed….in the process now.

[Jimmy]

I appreciate your 2 cents, believe me. I’m replacing that valve cover gasket this week. Fortunately, they come with the spark plug gaskets built into it. Thanks again!

[Jimmy]

Ok, changed the valve cover gasket. Didn’t help, although I did learn something from doing it, so not a total loss for $20 and a half hour or so of my time.

Cylinder # 4, where the misfire occurs, is fouling out the plug. Other 3 cylinder plugs look fine.

I’m pretty much left with two other things to try, but not sure if either or both is worth a shot.

EGR?
Replacing the fuel injector(s)

With the car running, I pulled the power plug to the EGR at idle. I did not drive it unplugged. I didn’t hear any difference in engine idle or otherwise. Should I have heard an engine change in
RPM?

And any idea WHY the poof of smoke would come out of my exhaust after only stopping at a downhill stop? Is the oil moving to the front of something, and then escaping out of the exhaust? I don’t understand the concept.

[Jimmy]

Karl,

I greatly appreciate the information and I understand what you’re saying. I guess my next question is whether or not it’s worth repairing/replacing, as the value of a repair is probably more than the car is worth. I don’t know what’s involved with the “ring issue” and I clearly can’t do this job myself. I neither have the tools or the know-how. What is the repair, and what’s the average cost of that repair.

Gotta run but will check back later. Your responses are greatly appreciated and welcomed.

Thanks again.

[Daniel]

If you get a puff of smoke at start-up but not under acceleration, then it’s valve guide seals. If it smokes while idling and/or under acceleration then it’s probably rings. I was thinking it may be a pcv valve but that would affect all four spark plugs.
I’m not sure what your skill level is but, it is actually relatively easy to replace the valve guide seals. This service can be performed with the engine in the vehicle and is not very invasive. It also does not require many specialty tools.
Piston rings are labor intensive and (to ensure proper installation) requires the engine to be removed from the car.

[Author]

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