xbdition

I have a new 2011 XB with only about 1500 miles on it. Since I bought it a couple months back, the engine at times sounds quite thrashy and mpg isn't that great, and as the title states, idle is rough, engine bogs pulling away from a stop with a hard stumble, and is low on power.

However, every once in a while it runs great. Power is smooth and strong, engine is quiet, and response is snappy and connected.

I've read that adding fuel injector cleaner can help, but does it make sense that without any sort of cleaner, and on the same tank of gas, these problems come and go?

I checked my engine oil level to make sure it wasn't overfilled or underfilled, and it is at about 3/4 level between the dots on the dipstick.

Any technical input would be appreciated.

bignoog

If it's brand new then this isn't your problem to solve. Take it back to the dealer and make them fix it. Bumper to Bumper!

xbdition

I deleted the last sentence of my original post wherein I wrote to please refrain from telling me to just take it to the dealer, and replaced it with asking for technical input. I didn't want to have to go into it, but taking it to the dealer and leaving it there is no simple task for me. Also, my experience with dealers is that they will say, "No codes, no problem" and send me on my way after wasting a day.

I suppose I'll take the first step of running some seafoam through it, and see how it goes. However, I'd also appreciate some technical feedback if anyone has any ideas.

tweetertc

now as you said... the vehicle has 1500 miles on it?... my first thought would be a tank of bad gas, but you say it comes and goes.. any possibility that these symptoms come and go as you use your AC... the ac compressor running can make these cars seemingly weak off the line and idle a little poorly.. i have noticed it on corolla's and and tc's..

is there any consistency in when your car performs poorly i.e. temperature, humidity, long drives, short drives anything... little things as such can help out huge

now just because your car has no check engine light doesn't mean with the right technician behind a decent scan tool he cant find a problem. i would honestly bring it to the dealer or a reputable drive-ability mechanic to have a look see, it seems its not the easiest for you... but you should make time for it, its best to have it looked at before it gets really bad... any further details could possibly help

xbdition

The ac compressor was suspect to me also, but unless the compressor turns on and off by itself occasionally without me having the fan on, then I doubt that is the issue. I leave the AC button depressed all the time, but the compressor isn't working unless I have the fan on right?

Just last night however, I drove with the AC button disengaged, and still had the issue. It doesn't seem to be weather dependent either, as it happens during the day, night, from the spring, and into this summer, all intermittently.

The perplexing thing is that the car's character will change sometimes within the same drive. So it may start running well, but by the end of my trip, it will have gone back to its odd behavior, or vice versa.

I know, its all quite confusing. Perhaps I can ask a more pointed question to start narrowing down the possibilities.

First, does anyone know what the MAF reading should be at idle for the 2az engine?

TrevorS

iTrader: (1)

Your description suggests the misbehavior is typical, not the exception -- I'd definitely try the dealer and if they talk in terms of codes, try a different dealer. At worst, try contacting Scion directly and describe to them what you're experiencing. You absolutely should not need to run Seafoam through it, 1500 miles is not enough to build enough deposits to hurt your engine's operation, and if it were, it wouldn't come and go. I could think of it as a moisture related problem, but you say nothing about rain. If it's not gas fill-up related, then there is probably an electronics problem, an intermittent sensor connector maybe? You say you never see any dash lights when the problem arises?

tweetertc

what you could try.. just a quick test... next time its running poorly you could pull over.. and disconnect the MAF then see if the idle improves.. its a super quick test and could tell eliminate a possible problem.. you'll get a check engine for MAF open circuit.. but you can always clear it..

i wish it wasnt the weekend i would run out at work and hop in a xb to see if i can duplicate the problem to see if its normal or not..

your not in the Chicago area by chance are ya?... i would take a quick look at it for ya..

xbdition

Rain? Never heard of it.

Damnit, took the car out for an errand and its purring like a kitten and running smooth as butter. Not a damn thing changed between the two runs I made today.

Our cars have a VVT-i solenoid like the H cars with their VTEC right? I wonder if that switch is causing my problems.

I'm going to try to figure something about taking it to a dealer, but its a larger PITA for me than anyone would reasonably guess.

Trevor, you think they'll void my warranty for swapping crossover capacitors?

TrevorS

iTrader: (1)

Not a chance on voiding your warranty! Your situation, as you present it, is a major drag, and I wish I could provide more assistance ! I'm not familiar with a VVT-i solenoid (though I'm aware VVT-i is controlled via oil pressure). I'd love to learn the solution to your problem, but I'm unable to predict it ! Still, the 2AZ-FE has been around for at least nine years and so your problem shouldn't be a complete mystery.

xbdition

I know I'm bringing this back from the dead, but I think I've resolved the problem. My car has just shy of 5000 miles now and I just reset the fuel trims via an OBDII scan tool. Afterwards the idle is rock solid, acceleration is consistent and strong, and mpg's are way up.

I knew that resetting the ECU is recommended when adding aftermarket parts, but my car is bone stock and was behaving strangely from the get go and so never considered it. I think the ECU parameters were way off from stock because the car was sitting on a lot with cheap and old gas for a long time.

Now that everything is reset, its smooth as butter. Curious though that nothing was reset when I disconnected my battery. Ah well.

Now to tackle a bit of NVH.

TrevorS

iTrader: (1)

So you're suggesting the entire problem was the need to perform an ECU reset? Interesting! Hope it continues behaving for you !