07 Yaris Sedan rough idle after sitting

[blain]

So what I have here is a 2007 Yaris Sedan, the unit has roughly 198K miles on it and generally runs like new. But over the last year I have started to notice that after the car sits unused for a couple of days (think parked on Friday after work and not started until Monday morning) the unit wants to run rough. The problem is compounded if I have to start the unit for a very short period of time (think moving it a couple of feet to access a work bench in a garage) and shut it down in under a minute. The issue on Monday morning is 10x worse and possibly takes 3x as long to get started. This morning was one of those bad ones and started but ran rough, I then noticed for the first time with this issues the CEL was illuminated. Anyone have a suggestion on where to start or what might be the problem.

[WeeYari]

Originally Posted by blain

CEL was illuminated

Get that read. That is your first concrete starting point.

Next easy thing would be to clean the MAF sensor.

[scratchpaddy]

Lots of parts stores, like Autozone, will scan your codes for free, if you don't have a scanner.

[blain]

Okay, so I pulled the codes last night and it showed a misfire on cylinders 2-4 at the time of the rough idle. So the question becomes why do I have a misfire after two days of sitting in a nice warm garage.

[Motzking1]

What do cylinders 2 and 4 have in common? If you can answer that you will likely answer your question.

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[dogsridewith]

um. they're both next to 3?

[Motzking1]

That is true. I was looking for more like they both have manafold vacuum ports, common ignition coil in a waisted spark system, something more along those lines. But thank you that was funny and witty!
I thought about it. I can't come up with much in my head besides they are companion cylinders. We look for the similarities because it's not likely 2 separate components simultaneously failed. There are very few things the cylinders have in common. And there are a lot of things we can eliminate that they do not. This is just kind of a good way I'm breaking down the possibilities to fewer components.
I like to break it down all the way to the most basic. In order for a cylinder to fire it must have only three things
1) proper air fuel ratio
2) compression
3) timed Spark
So when you first started up you're missing one of these. And then when it gets warm the missing one somehow comes back? Kind of an odd situation. Do you have a misfire code on two and four so we would look for what is similar between two and four. I can't come up with the whole lot besides their Companion cylinders.
So I'm going to take a blind stab at this one based on experience. I'm going to throw out a scenario with here and you think about it tell me what you think.

On Friday when you park the the car in the garage you turn the key off and walk away from the car. Hypothetically speaking let's say your number two or number 4 or less likely both fuel injector were really dirty (200k mi there is a good chance) and some of that grime was blocking the pental and seat in the tip of the fuel injector. Causing a very very small leak of fuel into the intake tract. Now normally the fuel injection pressure would remain in the fuel injection system for quite a long time. But in this case it's slowly leak out of the fuel injector or inject tours the next couple days saturating the intake manifold or cylinder with liquid fuel. Being as the intake manifold is a closed system it's sits there just like it would in your gas tank in liquid form. Couple days later you come to start your car on Monday morning and it has a pool of fuel in intake manifold causing an overly rich condition. You have to crank quite a while to bring her through there and evaporate that liquid fuel. When you crank long enough and you get that fuel out of there finally starts to fire up spits and sputters a little because you still have to much fuel on there. As it warms up it finally evaporates all that excess fuel. Now the engine computer is able to control its air fuel ratio properly and it runs good.

Now let's run that same scenario when you start it for one minute to move it. You crank and crank and crank and crank and crank you get it started. You move it to get it out of the garage and you shut it down again. It didn't really run it long enough to eliminate that pool of fuel in the intake manifold just long enough to get it to start and move so they're so like 50% of that fuel still left in it. Then you turn it off and let it sit for another day or two and leek a whole nother puddle of fuel in there on top of that 50% you still haven't burned yet. Let it sit and saturate then try to start it again in a couple days and now it's really difficult to start.
That's just a theory. One that is very easy to test. Install a fuel pressure Guage start the car. Turn it off and see how much the pressure dropped over time.
I do not know what Toyotas exceptable specification is???
But you're looking for a pretty big leak over time I would say if the fuel pressure cuts and half within a couple hours something's wrong.
Like I said that's just a theory based on my experience. Take what you want from it


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[blain]

Thanks for the reply's. To be clear when I say "cylinders 2-4" what I mean is cylinders 2 thru 4 (2,3,4). The injector theory is interesting. When I pulled the codes I did do a power balance test and it was acted the same when I shut down a single cylinder. I will try a tank of injector cleaner to see if that helps. Best to my memory I do not recall ever doing this so maybe it will help. Also as a side note I did do plugs when the car was at 130k.

[Motzking1]

Injector cleaner in not likely to fix the problem unfortunately. It's kind of like flushing your cooling system when its rusty and your radiator is pluged up. The problem is a part failure at that point. Not to say it could not help, just very unlikely.
The best course of action is the fuel pressure test.
If that's beyond your ability there are some other more crude methods of testing. Let the car run till it gets hot and is running well then pull the fuel pump fuse and attempt to keep it running as long as it will run that will take at least a fair amount of pressure out of the fuel injection system. Do that on Friday when you're going to let it sit for a couple days when you go to start it back up crank several times with a fuel injection fuse out. Then replace the fuse and see if it fires right back up. If it does it's definitely fuel-related

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[Motzking1]

That is kind of a really crude way of doing it but it should work

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[JimKellyfan]

Originally Posted by dogsridewith

um. they're both next to 3?

LMFFAO

[JimKellyfan]

If no misfire on cylinder 1, I would take a coil from 2, 3 or 4 and swap with one, clear codes and see if misfire moved to 1.

If not, then flip spark plugs too.

Make sure NGK or my choice Denso.

For sticky throttle, clean throttle plate.