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95.5-2004 Tacomas & 96-2002 4Runners 4th gen pickups and 3rd gen 4Runners

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Old 06-14-2011, 05:05 PM   #1
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rough idle like misfire (but no codes)

Hi, new member here

I have a '98 3.4L 4Runner. About a 2 years ago it started idling rough then a few days later check engine light came on and then started flashing and there was a weird "burning plastic" smell. Well, it was diagnosed as a bad #3 coil. Its was replaced and plugs and wires were also replaced at that time. But only the bad coil was replaced - not the other two.

Flash forward to last week and it has started to idle rough again. I have a code reader and there are no codes. Code reader does say that Catalytic converter is "not ready" that's in the IM section of the reader. Not sure if this is normal or not. Basically, its rot really a rough idle but rather more like a misfile (but no codes). So, do you think other coils are going bad? Replace the coils and plugs again? Any other ideas?

Thanks
-Bob
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Old 06-15-2011, 08:55 AM   #2
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Does it smooth out when you start driving it?
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Old 06-16-2011, 05:00 PM   #3
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Does it smooth out when you start driving it?
Yea, when driving it seems ok but when you stop and let it idle or about 15 seconds the rps drop to abut 600 and the engine its to "put put put". The idle will jump up to 800 rpm and then it seems better but it will drop down again and feels rough. It feels like a miss fire but I have no codes.

I have 2 new Denso coils from RockAuto.com on order and today I bought a new air filter and 6 new NGK BKR5EKB-11 plugs. If the problem persists after replacing these parts I'll be back to square one so any other idea would be welcome.

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-Bob
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Old 06-16-2011, 07:22 PM   #4
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sounds like its a plug boot that could be breaking down at idle, when you pull them out to replace plugs look for tell tale black streaks on the coil boots or on the 3 plug boots. it could get worse in the next couple of days.
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Old 06-17-2011, 05:24 AM   #5
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sounds like its a plug boot that could be breaking down at idle, when you pull them out to replace plugs look for tell tale black streaks on the coil boots or on the 3 plug boots. it could get worse in the next couple of days.
Ok, I'll look for that. Do you think I should replace the wire set also? Wires (NGK TE66) were last replaced October '99 so not that long ago.
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Old 06-17-2011, 09:18 AM   #6
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Have you had a fuel system service lately?
this happens alot on chevrolet's due to alot of carbon build up around the throttle body. It could also be another coil going bad. does the scanner you have have the ability to check mode 6 or a missfire counter?
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Old 06-17-2011, 12:12 PM   #7
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Have you had a fuel system service lately?
this happens alot on chevrolet's due to alot of carbon build up around the throttle body. It could also be another coil going bad. does the scanner you have have the ability to check mode 6 or a missfire counter?
No I have not had the fuel system serviced. I have not changed the fuel filter lately (ever?) either. I don't think my scanner gives that data. Its a real cheap scanner I got from Harbor Freight real similar to this one:

http://www.harborfreight.com/can-obd...enu-98568.html
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Old 06-18-2011, 07:33 AM   #8
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sorta hijack, but my 91 3.0 truck started doing this only when cold, but once its at operating temps, it runs perfectly smooth.
but unplugging the cold start injector doesnt change anything...
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Old 06-18-2011, 07:56 AM   #9
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ohm meter the wire set, should be no more then 25k ohms, look at plug wires for teltale burn marks, look at plugs as well for burn marks, and good fuel service never hurts, plus factory filter replace atleast every 60k is good idea, toyota does not have liture on R&R for it but most techs i know like 60-100k interval,

Even the factoy scan tool does not show fuel pressure as of yet in its data sream because it is not monitered, by watching the data list and sensors you can determine if its lean or rich but it does take a while to learn the values and what ones to watch.
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Old 06-18-2011, 09:28 AM   #10
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UPDATE: I just replaced the spark plugs and the two original coils. Problem NOT fixed Still pretty much the same. After the car warms up and if I then let it sit and idle for a few minutes it cycles between running fine (700rpm) and then rough (drops to 550rpm). The rough cycle lasts about 5 seconds and then its fine for about 15 seconds. Repeats this way.

I did not see any burn marks on the wire boots and the spark plugs still looked very good - replaced anyway. I did not see any signs of ware on the old coils - replaced anyway.

I'm going to swap in one of the old coils for the #3 coil. The #3 was replaced 2 years ago. I don't suspect that will make a difference but its worth a try.

Its really difficult to listen to the fuel injectors especially the ones on the driver side under the intake. I put my ear in there and tried to concentrate on them. It did seem that the #6 injector was louder than the rest. Sounded like a washing machine instead of the clicking that is more usual.

My scanner is really only for emissions (IM) ready check and OBDII codes. It doesn't give any diagnostic info. I do have a fuel pressure gauge with a schrader port connector. Does the 4Runner have a schrader diag port? I could look into that and see if the pressure is dropping during the rough cycle.

diagnosis continues ...
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Old 06-18-2011, 09:28 AM
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4runner, burning, check, code, engine, idle, idling, light, misfire, plastic, plugs, replace, rough, smell, spark, wires

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