Help! Intermittent Misfire Problems

[dwade]

I need help from all you 4Runner gurus. I’ve got a 1999 Toyota 4Runner (3.4L engine) with 195k miles. I’ve owned it for about three years. The CEL has been off and on some since I bought it, but the engine always ran fine. The plugs and wires were replaced about 1 year ago.

Lately I’ve been having problems with the engine running rough. Typically the engine runs smoothly for the trip to town (15 – 30 minutes one way). But then after running an errand and starting the engine back up it runs rough. Sometimes it runs a little rough (probably misfiring on one cylinder) and sometimes it runs really rough (probably misfiring on two cylinders). Once the engine sits parked for several hours (or overnight), it runs smoothly again.

One odd thing that has happened a couple times while the engine was running really rough is that it feels like there is a strong cough or lurch (like the engine almost died). As soon as that occurs, the engine runs smoothly again the rest of the way home.

I picked up an engine code scanner and started monitoring the fault codes. After checking the codes, I reset them and drive some more before checking again. Each time I check the codes I get some variation of the following list:

• P0120 – Throttle/Pedal Position Sensor/Switch A Circuit
• P0171 – System too Lean (Bank 1)
• P0300 – Random/Multiple Cylinder Misfire Detected
• P0302 – Cylinder 2 Misfire Detected
• P0303 – Cylinder 3 Misfire Detected

One time I also received the following code on a very cold morning:

• P0125 – Insufficient Coolant Temp for Closed Loop Fuel Control

I’ve seen in a few posts were people had troubles with antifreeze getting into cylinder 3 from a leaking head gasket or cracked head. I don’t think that is my problem because the exhaust is not white, it does not have that sweet antifreeze smell, and I don’t appear to be losing any coolant. The exhaust does have a strong smell, although I’m not sure if it is due to fuel or oil or something else????

Please help me to sort out what’s causing the issue with misfiring. What are the cheaper and easier things to start with? How can I narrow the problem down further?

Thanks,
Derek

 

[tyr0981]

all of my misfire issues, all three of them, have been spark plug & spark plug related issues. Very unlikely to be a coil issue, to test a coil, move the coils to other cylinder and see if the issue follows it. Plugs and wires are cheap & easy, and should be replaced often anyway!

happy hunting! :driving:

edit: oh and Bosch plugs are fukin garbage! never ever buy them!

 

[Doc2012]

Is your truck a Cali emissions or a Federal?

Your 120, 171, and 125 could be from the TPS. That said, all the codes could be from the TPS. The 125 could be from a bad O2 sensor as well.

If you replaced the plugs and wires a year ago, the wires should be fine.

My course would be to change the TPS, see if that fixes it. Minus well do the plugs while you're at it. If that takes care of it, you're good. If you're still getting the 125, replace the front o2 sensor.

 

[Jayzero911]

Sounds like TPS to me, and the codes really point that way.

I have been a bad boy and haven't changed my plugs and wires in 2-3 years ago in my '02.... but no problems..... almost fell off the toilet when I recalled the last time I changed them....

 

[dwade]

Is your truck a Cali emissions or a Federal?

Well, I thought the fellow I bought the 4Runner from said he got it new in California; however, when I look underneath I only see one catalytic converter. My understanding is that for 1999 models one catalytic converter means they are Federal.

I am attaching a copy of the emissions sticker in case that helps answer the question for sure. I live in Kansas and emissions tests are not required here.

 

[TheDurk]

I would have agreed with you, but when I put that engine family code into the CARB data base I get this:

http://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/1999/toyota_ldt_a0140352_3d4_t.pdf

I therefore conclude that this is a single-cat Federal-type system that was legal for sale in California. I bet its production date is very early in the run, (start is 07/1998) In fact, I bet he bought it in '98. I own a '99 Cali. 3,4 V6 purchased in NJ and date 03/99 and it is a two-cat Cali.-type. Totally different label. Yours is a TLEV Transitional Low Emissions Vehicle. Mine is an NLEV New Low Emissions Vehicle, has lots of verbiage about legal for sale in Cali, and says CAL & OTC where yours says FEDERAL & CANADA. and says TWC(2) where yours says TWC, signifying two cats versus one (TWC=three-way converter)

 

[TFJ-4runner]

Might of jumped timing

 

[dwade]

I therefore conclude that this is a single-cat Federal-type system that was legal for sale in California. I bet its production date is very early in the run, (start is 07/1998) In fact, I bet he bought it in '98.

I'd say you're right, TheDurk. The sticker in the driver side door shows the date of 10/98.

 

[george16]

Check and make sure your spark plugs are torqued properly. Check you intake hoses and make sure the hose clamps are tight.

I just got rid of the hesitation when my truck is running due to the vacuum leak caused by the loose clamps on the intake hose to the throttle body. The dealer probably did this after they replaced the timing belt last august.

I replaced the spark plugs and the front spark plug on the passenger side was very loose and see black soot/fuel deposit inside the spark plug well.

 

[dwade]

Well, I replaced the TPS tonight (with a new one), reset the ECU, and took her for a test drive. The problem with the rough running engine appears unchanged. The engine was nice and smooth on the way to town. Then after sitting parked (and turned off) for 15 minutes, the engine ran really rough on the way home.

One odd thing was that the CEL did not come on at all on the way home. Out of curiosity I checked for fault codes once I was back home and the ECU reported that P0303 (Cylinder 3 misfire) had occurred (even though there was no CEL).

I will have to drive it some more to figure out if the other fault codes return or not. I'm hoping that at least the P0120 (TPS A Circuit) will be resolved.

I sure appreciate all the great input from the forum members. What is the next logical choice on diagnosing / fixing the misfire problem?

BTW - I ran across this post where joeflem had a really similar sounding problem that ultimately turned out to be injectors. Do I need to be testing the injectors somehow?

 

[dwade]

Well, during my second short trip to town the vehicle still behaved the same. It ran fine on the way to town and ran rough on the way home. The CEL has still not come on. Using Torque I can see that the following faults have occurred since I reset the ECU last night:

• P0171 – System too Lean (Bank 1)
• P0300 – Random/Multiple Cylinder Misfire Detected
• P0302 – Cylinder 2 Misfire Detected
• P0303 – Cylinder 3 Misfire Detected

So far the P0120 (TPS A Circuit) has not returned although I've only made two short trips since swapping out the TPS late last night.

How can I narrow down if this is electrical or fuel related? If the misfiring cylinders were on the same coil pack I would probably head that direction next, but they are not.

One other detail I forgot to mention is that I ran 4 or 5 tanks of gas through using fuel injector cleaner when the problem first started. Fuel injector cleaner did not seem to improve the issue in any way.

 

[dwade]

Latest update. I did some digging on the forum and found how to test the fuel injector coils with an ohm meter.

I was able to easily test the injectors for cylinders 1, 3, and 5 (since they are not under the plenum). Here are the results:

Cylinder 5 = 14.7 ohms​

Cylinder 3 = 31.4 ohms​

Cylinder 1 = 14.1 ohms​

Aha! The resistance should be close to 15 ohms and #3 is way out of spec. I wish I could easily get at cylinder 2's fuel injector so I could test the resistance and know for sure if it has the same issue, but I cannot.

Unfortunately I don't have the time or experience to handle fuel injector replacements myself, so I have an appointment scheduled with a mechanic for Monday morning. I was hoping the problem would be simpler to fix (i.e. plugs / coil packs / etc.).

I'll post another status update once the vehicle is back from the shop.

 

[dwade]

The 4 Runner is back from the shop and is running great! The #3 fuel injector was bad and had actually come apart (the mechanic said it came out in two pieces). The other 5 injectors were all tested and cleaned and they were fine. The issue with #3 was causing all of the remaining fault codes.

The mechanic said the #2 misfire was due to the fact that it was in line with #3 on the intake manifold.

Anyway, thanks for all the input and advice.

 

[Meidschun]

I know this thread is super old but I need help....

I have a 2002 sport 4x4 with the 3.4...195k
A few weeks ago the truck started to misfire and threw codes indicating such. I replaced the spark plug for that cylinder and seemed to fix the problem. Fast forward to a couple days ago and the truck is missing and sputtering once again and isn't even drivable, no codes this time at all. I then changed all six plugs (ngk duel electrodes) new plug wires, cleaned the maf and throttle body. After this the truck ran good for two days. Then it started again, hit or mis. Try to crank it and nothing, do it again and it works...all with no codes ever being thrown. So yesterday I dug in....checked the plugs and wires. Continuity check good. Checked the ohms on the fuel injectors...all 16.4-16.5 ohms. Took the injectors out and tested them and they seemed to spray great. I double checked everything and put it back together and now it won't even start. I did notice when I changed the plugs a small amount of oil in the tube so I will address this with new seals but I do not think this is my problem. No leaking around the valve covers. All vacuum lines look good.
I have been online reseaching the crap out of this and most people get codes and this helps narrow it down....I don't want to spend a fortune fixing it.
I have so far replaced or done
Fuel filter
New plugs ngk
New wires (dura last)
Cleans MAF
Cleaned throttle body
Cleaned injectors and tested resistance
Sea foam into intake

It seems to be a fuel problem...I think. Should I test the FPR? Bad fuel pump? Still could be an injector so I've read? Gonna do a compression check today but this is my family car and need it to haul the kids. Any help would be appreciated

 

[Dangerdan23]

Engine misfiring randomly with no CEL

Picked up a 2000 4runner SR5 V6 about a month ago. Every once and a while it will misfire pretty bad (whole cab is shaking under acceleration/at idle) scanned it for codes but nothing came up. My code reader however is showing red icons for EVA 02S CAT and HTR. most of the time it is running fine. Is this something i should bring into my mechanic ASAP?

 

[TheDurk]

Picked up a 2000 4runner SR5 V6 about a month ago. Every once and a while it will misfire pretty bad (whole cab is shaking under acceleration/at idle) scanned it for codes but nothing came up. My code reader however is showing red icons for EVA 02S CAT and HTR. most of the time it is running fine. Is this something i should bring into my mechanic ASAP?

Well, I would much prefer to have the code numbers rather than what some stupid code reader interprets them as. But it sounds like a bad O2 sensor and that can cause all kinds of issues. Give us the numbers if you want decent advice. Never trust what the reader says it is. Use the Toyota FSM and the numbers or you will waste time and money.

 

[Buckaroo]

Is this something i should bring into my mechanic ASAP?

This is something that you should resolve relatively quickly. Continuing misfires can fry your catalytic converter.

Buckaroo

 

[hintz1031]

1999 4Runner SR5 3.4

I bought a 1999 4Runner SR5 about a month ago. It had a misfire when I bough it, and was told it was a bad fuel injector. I took it to my mechanic to diagnose the issue, and he said it was not getting fuel from the injector on #4, but had good compression and strong spark.

I went ahead and replaced all 6 injectors, spark plugs, and did the valve cover gaskets myself while I was in there. Took it for a test drive and it ran great for the first several miles, but then started running rough like a misfire again. It didn't throw a code though. Drove it about 5 miles the next morning and it ran great the whole way. On my way home later in the day it ran great for the first couple miles again, but then started missing the rest of the way back.

Any ideas on this? could it be a vacuum leak?

 

[Buckaroo]

Hintz1031 -

With the limited info provided, I would start by looking at ignition and injectors as they can fail intermittently as they heat up. Also O2 sensor because you enter closed-loop control which utilizes the O2 sensor after reaching operating temp. Resist the temptation to just start replacing stuff (can get very expensive) - do the diagnosis and attempt to verify the problem before hanging new parts.

Easy stuff first - Make sure that the electrical connections on the injectors and the spark plugs are seated firmly. Make sure your vacuum lines are all connected. Check your spark plug wire routing to make sure it's correct. Do a visual on the O2 sensor connection (primarily focus on the one if front of the Cat) and make sure the wiring looks good and the connectors are seated.

Where did you get the injectors? New or rebuilt? Have the O2 sensors ever been replaced? If so, were they Denso?

Buckaroo