420 error code and also high idle

[Langcow1]

Two things occurring with my 4runner that may or may not be connected… In the Spring I had the check engine light on with the 420 code and also several misfire codes. Since then I’ve done a bunch of work on it fixing many things, including a tuneup with new O2 sensors, and also a new (reconditioned) set of Motorwest injectors. These seemed to have resolved the check engine light issues and it’s been running well.

Recently I went on a 600 mile roundtrip roadtrip and the rig ran great. 30 miles from home though, the stupid check engine light came back on. 420 code again. I think I should reset it and see if it comes back — there’s always a remote chance that the Oregon gas pumping guy didn’t get the gas cap back on tight.

I have also recently noticed that it idles around 1700 rpm when I first start it up, and then this gradually decreases as I drive a few miles until it finally settles in around 800-ish once it’s warm. I’m not sure if it was doing this before the check engine light came back on so I don’t know if it is connected or not. I do think it is something relatively new — IIRC it was simply idling around 800 all the time after I completed the tuneup.

Definitely appreciate any thoughts and advice. It does seem to be running alright overall at the moment.

 

[RandyBobandy]

P0420 is a catalyst code I think? If you replaced both your o2 sensors with good denso sensors and not aftermarket junk your catalytic converter could be the issue, there’s a thread on here somewhere about how to make a rear o2 simulator to get rid of that code without having to buy a new cat

 

[shadow247]

P0420 is a catalyst code I think? If you replaced both your o2 sensors with good denso sensors and not aftermarket junk your catalytic converter could be the issue, there’s a thread on here somewhere about how to make a rear o2 simulator to get rid of that code without having to buy a new cat

Just buy the URD simulator for like 80 bucks. No sweat, plugs in and you are done. Mine is still running strong since 2014.

 

[Devbot]

Huh funny, I'm in nearly the same exact boat. Had it thrown last year, replaced both sensors with OEM, was good until a couple weeks ago. It's not uncommon for P0420 to pop up randomly for us so feel free to clear it and pay more attention if it comes back.
If it does come back, the next steps I would take would be running some lacquer thinner, looking for exhaust leaks, clean the O2 sensors/check their bolts and maybe even replace their gaskets, etc - start cheap and work your way up. If you have a scanner that allows it, you can check your cat and O2 sensor efficiency and if it's a steady signal+within optimal range.
In the past I've seen some people pop out an O2 sensor, stick in a can of carb clean and blast away - that cleans them really damn good but I personally find that to be a little sketchy. Believe it or not when a cat sees a lot of unburned fuel over a decent period of time, it melts a tennis ball sized hole completely through the honeycomb; which is effectively what carb clean is, just a bunch of white spirits (xylol/toluene/naphtha). Granted a quick blast of it probably wont do any damage, it still worries me personally and should be done at your own risk. Adding lacquer thinner to your gas won't hurt a thing however.

 

[fathousecat_]

Interested to see what others say about the idle.

 

[RandyBobandy]

Just buy the URD simulator for like 80 bucks. No sweat, plugs in and you are done. Mine is still running strong since 2014.

That’s an option too if the op doesn’t want to do a diy simulator, however I can confirm from my own experience that the method in that thread does work very well too

 

[Bad Luck]

I have also recently noticed that it idles around 1700 rpm when I first start it up, and then this gradually decreases as I drive a few miles until it finally settles in around 800-ish once it’s warm. I’m not sure if it was doing this before the check engine light came back on so I don’t know if it is connected or not. I do think it is something relatively new — IIRC it was simply idling around 800 all the time after I completed the tuneup.

Definitely appreciate any thoughts and advice. It does seem to be running alright overall at the moment.

All 3rd gen's have a high idle until they warm up enough. Mine will idle around 1500-1600 rpm's when in park until it warms up enough. Normal operation.

 

[19963.4lsr5]

Yes, the first cold start high idle is normal. As soon as the pre-cat O2 sensor warms up the pcm goes closed loop and you notice the idle start to drop.

I never had luck making the O2 simulator work. It never reset my P0420 code. And I figured if it wouldn’t reset it then it wouldn’t allow the readiness monitor set either if I cleared the code. My cause was from it burning antifreeze.


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[gamefreakgc]

Idle speed really varies based on a lot of different factors. One of the biggest is ambient air temperature and the coolant temperature. If the coolant doesn't hit near 170 degrees the idle will increase slightly to keep the engine warm. Consequently in the summer, if it gets very warm near 100 degrees and the coolant around 200-210 the idle speed will drop a little. This may also be because of the lack of air density and the MAF voltage reading is lower when the air is hot. All that being said, it's hard to make a judgement if 800 RPM at idle is "bad" or "good". For the most part it's just a side effect of something else. If you are really bugged by it there IS a way to manually adjust your idle speed but I don't recommend doing it if there's no ill-effect of idling at 800 RPM.

 

[19963.4lsr5]

In my experience all three 3.4l equipped 4Runners I’ve owned…..it’s up to temp idled is 750 in park or neutral and 600 in gear with your foot on the brake.

I’ll admit I never seen 210 to observe the idle. And I had to block 80% of it just to hit 195 while testing a AFR PID for my ScanGauge. But my engine is fresh with new Rad, water pump, clutch for cooling fan, and a flushed/clean oil cooler.

I’ll check my 170 idle tomorrow. I thought my idle was normal by 165.


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[Langcow1]

Ok thanks everybody. I won’t sweat the idle. It always sounds smooth to me, just higher and then lower once warm.

For the 420 code, I’m going to reset and then see what happens on my next road trip in a couple of weeks. I won’t be in OR this time so I’ll be curious whether or not the CEL comes back on. It seems like it often comes on after gassing up in OR.

 

[Honda pc]

here is the post I created....almost same as yours...

Code PO420 PASS/NO PASS smog test??

I am working on same thing here in socal.... still testing it out...its a pending light warning....not a full check engine code 420 yet.... But it was before...had a code 420 and full check engine light.... I reset it and started on 3 tanks of 92 octane diet.... and have since no check engine lite....have only pending 420 data on reader...
so I am really thinking of taking it to test emission soon... right now... I loaded up 1 gallon of lacquer thinner with 1/2 tank gas 92 octane... running that out and will load up 2 more tanks of 92 to see what happens...

have not done the infared temp check yet.... or clean cat, O2 sensor yet...

I am thinking I might pass with a pending 420...since I don;t have a real check engine code lit or a real fail code 420 yet.... I have done some 100 mile test runs ,,,high speed and low and what not....

another option seem to be doing a diode install in the O2 wiring...google it.

 

[DenverAirport]

I also know about the 420 code and high idling