V8 Misfire at idle

[4RunnerV8]

Long time since I've posted, but I've had what appears to be an unusual problem for a V8. Over the past few weeks, I've had a random misfire - rough idle - issue. At idle, particularly in drive, the engine sometimes stumbles badly. Almost to the point of shutting down, but if I accelerate or throw it in neutral and rev, it clear up until the next idle. The only things that have changed prior to this were 2 02 sensors, and a battery. O2 sensors were causing CEL to come on, and would have prevented successful emissions inspection. They were replaced by an independent mechanic that has a great reputation. It's only thrown codes once (at least codes I can read via Torque) and they were misfires on 2,4,6,8. They were also registered as pending codes...

Need some help on this - it does need a tune up - but the single side of the engine misfiring and only at idle seems to point to something different? Timing belt & water pump changed about 20K ago.

Any thoughts?

 

[gshadow325]

Long time since I've posted, but I've had what appears to be an unusual problem for a V8. Over the past few weeks, I've had a random misfire - rough idle - issue. At idle, particularly in drive, the engine sometimes stumbles badly. Almost to the point of shutting down, but if I accelerate or throw it in neutral and rev, it clear up until the next idle. The only things that have changed prior to this were 2 02 sensors, and a battery. O2 sensors were causing CEL to come on, and would have prevented successful emissions inspection. They were replaced by an independent mechanic that has a great reputation. It's only thrown codes once (at least codes I can read via Torque) and they were misfires on 2,4,6,8. They were also registered as pending codes...

Need some help on this - it does need a tune up - but the single side of the engine misfiring and only at idle seems to point to something different? Timing belt & water pump changed about 20K ago.

Any thoughts?

change your plugs. since it misfire on 2468 then move one to 135 or 7 see if the misfire follow you to that cylinder. if it does then lucky for you you have 4 bad coils

 

[4RunnerV8]

Thanks for the advice - it just seems really strange that everything ran perfectly until the O2 sensors were replaced, and that only one bank was affected. Could aftermarket 02 sensors cause problems upstream?

 

[BlackWorksInc]

How recently was the Timing Belt replaced? There's a bit of a trick to the Timing Belt when installing it, otherwise you can get one or both banks off a little and it COULD cause this type of issue.

 

[4RunnerV8]

Timing belt was replaced roughly 6 months ago (dealership)- car is at 232K now, and replaced timing belt at roughly 210K. I'd read about some timing belt and cam issues, but the issue came at roughly 229K, so a significant amount of time had passed. It was, however, the week after the 02 sensors were replaced. I was early for a client meeting and was idling in a parking lot while in drive, but stationary, and felt the misfiring - almost like it was going to stall. It's happened several times since then, and revving it or driving seems to eliminate the misfire. It seems worse when the A/C is on as well. When I let it go on, the CEL intermittently lights, and it throws pending codes for misfire on 2/4/6/8 and a miscellaneous misfire. Any thoughts? I figured I'd check the PCV for the helluvit, but couldn't it to unscrew - threaded valve. No other signs of a PCV problem (oil leaks, air filter issues, etc.)

Thanks for any help, folks!

2004 SE V8 4WD

 

[TRDCal]

I don't think it's possible for O2 sensor to cause a misfire. 4 bad plugs and/or coils seems unlikely but possible I guess, swapping them from side to side is always a good start for troubleshooting.

My guesses would be cam skipped a tooth, clogged cat, or maybe even a bad head gasket.

 

[4RunnerV8]

The only time I had a vehicle with a bad cat was several years ago - clogged, and the symptoms were an inability to rev very high, not stumbling at idle. But that was in the early 90's. I've never had an overheat, and haven't yet heard much at all about the 4.7 V8 having head gasket problems. Coolant level hasn't changed at all. The cam tooth does seem to be a serious possibility. I'm going to take it in to the shop today and see what they can find out, but I just don't want to start replacing items in a blind hunt. It does need a tune up, though.

 

[4RunnerV8]

One more thing - when the truck is cold, no problem - only happens after the vehicle is warmed up and idling for several minutes. From cold, idling for 10 minutes before misfire appears.

 

[97hb]

When your car is cold or warming up or at wot it is running open loop or off a predetermined fuel map. When warmed up its running closed loop using o2 feedback to maintain AF ratios. I would check those o2's especially if not OEM. I'm not a fan of non OEM sensors.

 

[4RunnerV8]

Any suggestions on how to test an installed 02 sensor to see if it's up to OEM quality/spec? I'm thinking along the same lines. Another issue is that the VSC/VSC TRac lights came on - no CEL - after the O2 sensor install, and after inspection. I read a thread about different scanners not being able to zero out the VSC system, or doing it incorrectly, and the pin short option for fixing. I'm guessing these two things are only slightly related.

 

[boondoggle]

I remember a while back some folks were posting about an issue with some of the VVTI V8's having an issue with some 'blower' thing (no, not a supercharger). I think the issue was opposite though, it would only give them a problem initially at startup. Can't remember what that thing was called.

With the high mileage on yours, I'm guessing it's not one of the VVTI V8s.

Probably not a helpful post, but perhaps it will jog someone else's memory...

 

[97hb]

Needs to be around 11-16 ohms around room temp. They show another way holding idle at 3k rpms for 3 min then testing with dlc3 or oscilloscope.

 

[4RunnerV8]

Thanks for all the suggestions and keep 'em rolling! It's not a vvti engine - I think that the variable valve timing showed up in 2005, and mine is an 04.

 

[progress4m]

When your car is cold or warming up or at wot it is running open loop or off a predetermined fuel map. When warmed up its running closed loop using o2 feedback to maintain AF ratios. I would check those o2's especially if not OEM. I'm not a fan of non OEM sensors.

I agree with that as well: check O2 sensor;
The other thing I would check is TPS (Throttle Position Sensor)

 

[4RunnerV8]

I'm guessing first 02 sensor would be the passenger side, since the misfires were on 2/4/6/8. I'm hoping the garage that installed the sensors will stand behind their work and the item they installed. No reason to think they won't.

 

[BlackWorksInc]

One more thing - when the truck is cold, no problem - only happens after the vehicle is warmed up and idling for several minutes. From cold, idling for 10 minutes before misfire appears.

This is something I saw consistently with some of the 3rd Gens I worked on. The injectors start to fail internally and when the vehicle gets hot enough the resistance is too great for the injector to function properly. Granted this is the first I have heard of it on a 4th gen or a 4.7L, but you have a serious amount of mileage on it at the moment so its a possibility...

Can you get a scantool and see if the pulse width of the injectors is the same on both banks?

 

[4RunnerV8]

Bump

Hey all - long time again. I ultimately replaced the rear o2 sensor, and changed the plugs. Things seemed a bit better, but in reality, I don't think I had a scenario where I idled for any time at all. The problem, however, is still there. I don't have access to a scantool for measuring fuel injector issues. It's still only when the vehicle has been running for a while, and at idle - in gear or park - that it comes back. Any additional ideas? I've had a mechanic - the one who replaced the o2 sensors - who said that it must be the cats. No indication whatsoever of cat problems - mileage as good as ever, acceleration and power as good as new. The only indication of cat problems is the code intermittently thrown when the truck is at idle. Another mechanic said that that p0420 code (I believe) can be completely unrelated to the cats in reality and is simply a symptom of another problem than the cats. I'm left with injectors, or the possibility that the initial 02 sensor (front) was faulty, as the issue didn't show up until that sensor was replaced. In full disclosure, the front 02 sensor had been bad for a bit less than a year. My mechanic told me not to worry unless driveability issues came up until I needed an emissions inspection. Prior to that inspection, I got the 02 sensor changed. Any help from this knowledge pool would be greatly appreciated!

 

[cloh09]

I also had a misfire on one cylinder. It was after 1000s of miles after a timing belt and spark plug replacement. I drove it from NJ down to South Carolina for vacation and that's when the problems started there. CEL came on and would flash when the vehicle was misfiring. Turns out it was a loose wire coming out of a distributor. I guess it was never clicked in and had rattled loose over time. Check to see if all the wires are tightly connected.
That was just my experience with a misfire. Haven't had a problem since, but I haven't replaced any o2 sensors yet, either.
Best of luck on your findings.

 

[4RunnerV8]

Thanks for the info. I may be a bit slow, but I thought these were distributorless ignitions. Where would I find the distributor?

 

[gshadow325]

I was thinking the sane thing, but I think he means not clicked on referring to the connector at the coil pack at the spark plug