Poor idle after cold start and a p0420 code.

99 prerunner 2.7 with 177k miles. So I had a check engine light for a bad IACV changed the part and the code went away. But than about 2 weeks later I started getting a rough idle and poor running engine for about 10-15 seconds after start up than it clears up and runs fine after that. Been dealing with that for about a month or more and now I threw a code again and it's a P0420 for o2 sensor limits low for bank 1

Anyone might know what's going on? Possibly leaking fuel injectors. Or even worse coolant leaking into a cylinder?

I did a block test last weekend and the fluid didn't turn yellow but it did turn a lighter blue almost clear.

Also the poor idle seems to go away if I restart it once it clears itself up. But if I let it sit for an hour or more it will usually come back. Although sometimes it doesn't. And after a long 3day weekend this weekend it seemed to start fairly fine, it only idled poorly for about 1-2 seconds.

 

Are you sure that the code was not PO420? 402 is excessive air flow or EGR issues. It has nothing to do with cats as far as I know.

PO420 is cat operation below threshold. Often an exhaust leak between the cat and the muffler can trigger that one. The exhaust flange is next to the Os sensor.

 

Yes that's it sorry. I get those 2 mixed up easily. So it's a P0420 and the P0402 was the one I had for the IAC valve that I fixed. I also do constantly have exhaust leaks with the Doug thorley header I have. And I'm pretty sure I have one again and been wanting to get in there and get it fixed but haven't had much time with work and a baby on the way. So maybe the code isn't related to the poor starting condition.

 

Like I said, check the O2 sensor gasket and the flange right next to it. Spray some soapy water on the areas and look for bubbles after you start the truck.

420 code can be a pain. It takes a lot to kill a cat on a Tacoma. As long as that CEL was not on for a long time, its most likely fine.

 

Ok will do, probably won't have anytime for the next few weeks to get in there. But I'll get back here after that's done. But I'm still curious to see if anyone's had similar poor idle after a cold start.

 

So no rough start this morning. Kinda odd but we'll see how it goes after work today

Also found out from a ase certified mechanic friend that if the fluid changes color at all even if a little bit that it failed the block test. There may be a little oil in my coolant hard to tell really without draining it, but there is for sure no bubbles or excess pressure

 

Ok so another update

Last 2 days I haven't had the rough idle when I started the car after sitting over night but after work yesterday if fired up way to quickly, almost instantly. Usually I hear the starter crank 2 times. Than this morning after sitting all night it started just fine But just now I had to leave work for an apointment and it started fine again than after I drove for about 45 min it sat for 30 min and when I fired it up it hesitated as if it almost didn't want to start but than it fired up with no rough idle.

This is so confusing and weird that after a few monthes of idling like shit for about 20 seconds after start up it just stops yet it's still doing odd stuff.

Although I remember it didn't always do it every time but it did it every morning. I'm just paying more attention now and logging it here.

I know it's almost pointless to ask for help without having the time to do diegnostics on it but I just would like to have a conversation about the symptoms with knowledgeable Toyota owners/mechanics

Soon enough here in a few weeks I'll have some time to get under the hood and run a compression test and a fuel injector leak test and get the exhaust leak snugged up.

I'll keep updating this thread with how the engine is acting during starts.

Oh and it runs fine other than the start up.

 

Your starting issues sound a bit like a leaking injector. I just replaced mine at 180K because I had a misfire code and some strange, inconsistent start-up issues. I found a set of 4 OEM injectors on ebay for under $100 and the job is fairly easy. And it fixed the problem.

 

Upon reviewing your mod list on your profile, I notice you have the infamous "gay ass" mod. Is this available through Toyota or do I need to try and track down a Gay ass on ebay. Thanks

 

That was my first thought but I'm not getting all the symptoms. No hard starting when warm, no misfire code.

I feel like my symptoms are more closely related to coolant weeping into a cylinder. But than

Ha I actually need to update that. Got rid of the gay ass mod last year

 

How much did you get for it. Sounds like it could have really, Penetrated, the market.

 

Well they penetrated as deep as 3 inches can go. But it was definitely hard to remove the from the crevices of my trucks body....had to grease them a little and get a friend to help.

 

Well the truck started great after work but I stopped at the groceries store after work and about 30 min later started the truck and it fired up way to quick again almost instantly.. as if it had fuel in the cylinder ready to ignite.

 

To update this thread my truck started consuming water like no tomorrow, and was burning about 1.5 letters of water every 60 miles. The poor idle at start up got worse but always cleared up still once the water was burned off. It even hydrolocked on day and I thought I bent a rod but it eventually fired up Borascoped the cylinders to find #4 looked like this and 1-3 looked like this

The truck has been parked now and I'm waiting to drop in a new engine. I will also be testing the fuel system and flushing the coolant system.