Mechanically illiterate dealing with random stalling

[Little Lady]

My 2008 Scion xD has has some issues the past few weeks. It occasionally idles pretty rough at red lights and a week ago it shuddered and stalled at a red light. There are no service indicators or malfunction lights and I was quickly able to restart it and continue driving it. Then a few days later it began to shudder at a stop light so I put it in park prepared to stall but doing so seemed to stop the shuddering and I was again able to continue driving it. I took it to a mechanic who ran a diagnostic, drove it and inspected it but found no problems. I made an appointment for tomorrow at the Toyota dealership here but I cringe at the thought of going there after being ripped off several times in the past by this place. It is my opinion that they prey upon mechanically illiterate military wives forced to deal with such issues alone. HELP! It's on schedule with oil changes and routine maintenance and it runs perfectly most of the time. What could it be?

[bobolinko]

Before you go there... Try this:

Go to a place like autozone or car quest or O'rilleys....

Ask the counter person for additive to remove water from the fuel tank, and a injector cleaner, (2 separate things) and pour them into the gas filler opening. Then go to a fuel station, and fill with premium gasoline.
It would be best to put the additives just when you're filling the gas, and would be most opportune to do it when the fuel is low and not almost full :>)

Good luck!
Don't go to the dealer just yet!!!!! By All Means..... They would most probably do an extraction from your pocketbook and just change the blinker fluid.

[HATEnFATE]

Well there Bobo, Not all dealers are like that but thanks for the vote of confidence.

The reason your xD quits wanting to die when you put it in park or neutral is that you're taking the "load" or restraint off of the engine when you do that so there is no drag coming from the transmission.

My first quiestion is now many miles are on your xD? Do you still have any warranty remaining? Keep in mind that this is possibly a powertrain issue and might be covered by the 5 year/60,000 mile powertrain warranty.

I do agree that doing some kind of a fuel flush might help the situation.
You might have an ignition coil starting to go out(it's a problem with the xB's though the engine's are not related and the coils are different)

There might possibly be an issue with the Mass Airflow Sensor. It might be a little dirty from the salt in the air if you are close to the ocean. It might just need to be cleaned/replaced.

The Throttle Body might be in the same situation as the Mass Airflow Sensor. Maybe some salt has crystalized on the inside of it, causing a port to become partially blocked?

I can think of a number of small things that could cause a "stumbling" issue like you are descibing. Not many of them are likely however if your car isn't setting off a "check engine" light or MIL(malfunction indicator lamp) as toyota refers to it. Since there is no light, whomever is looking at the car, be it a Toyota technician or a local mechanic that you trust, finding the problem will be a little difficult because there isn't a cut and dry spot that the car is telling him/her to look first.

Make sure when you take the car to Toyota, you tell the service advisor exactly what happened, when it happened, and what happened when you put the car in park/neutral.

P.S. Do NOT put in any fuel additive because it might make the problem harder to diagnose.