my 02TT was parked for about 2 weeks, this morning I took her out for a spin and she ran fine for about 10 mins, I stoped to get gas and inmediately after I started her the engine felt strange, the idle was erratic (very low) and if I pressed the gas the engine would hesitate (felt like PSM feels like when kicks in). I drove her home carefully, she would drive normaly above 2,5k rpms but if I pressed the gas a bit she would start hesitating again.. she is stock and has 28k miles. 6sp. got no CELs no noises, nothing...
I am seriously worried I hope is something minor.
It was cold outside (30F) could it be a bad MAF? any ideas?
Thanks

 

I have had this problem for a long time, ONLY happens after fill up and only for a few (annoying) minutes. Almost feels like the car is doing a split second power dump and makes the car buck slightly under acceleration. Never was able to diagnose it but exact same scenario as you described.

It will be interesting to see if it happens again when you fill up!

 

With no check engine light and thus no error codes to suggest a cause hard to say if cause minor or not. Chances are it is minor but likely hard to trouble-shoot. Mainly involves a process of elimination that is eliminating what are not the causes until, well, until you find something you can't eliminate.

Generally last thing touched is always suspect #1 so that the car ran fine until you stopped to get gas suggests to me "bad" gas. I hate this explanation cause I have a hard time imagining how the gas could be so bad as to cause the symptoms. OTOH, some stations move so little gas and premium gas moves even slower, the gas may be quite stale. But it would have to be real stale I would think to cause the symptoms you describe.

As an aside: You want to buy gas from a busy station to ensure you get fresh gas. Fuel tests have shown that gasoline -- premium anyhow -- can lose some of its premium characteristics after some time (few weeks), so buying gas from a busy station ensures you'll get gas that is as fresh as it can be. (I've talked with some gas tank delivery truck drivers and some report they make deliveries several times a day to the busiest stations -- one in particular was the Shell station in I-35 in Olathe KS, where a driver told me at some times of the year he made up to 4 deliveries a day to this station.) This gives you some cushion against the gas going stale while in the gas tank if the car sits unused for awhile.

Next any time I hear/read of any car that has sat unused for a while then acts up upon its next use, I always think "rodents". At the right time of the year, it doesn't take much time for rodents (mice or rats) to set up housekeeping in a car.

Be sure to give car a good inspection looking for signs of rodent presence. Check the engine air filter element and air box for any signs. Look back into engine compartment as best you can. Use bright flash light. Look down on top of engine, all around engine and engine compartment. Also, look at top surfaces of engine and underbody panels for presence of rodent litter, leaves, grass, droppings, etc.

I came across a Turbo Cab in dealership service bay that had rodents and the reason it was brought in was the engine was not running right.

Once the tech had a look it was clear rodents had gotten into the car and had done considerable damage, gnawing their way through the rear seats and into the engine compartment, where they chewed upon hoses, and the engine wiring harness. Engine/tranny had to come out and the extent of the damage assessed. Expensive to put right.

If you want, if symptoms are still present, you can unplug MAF from wiring harness and then start engine and drive the car, normally, and see if symptoms still present. If not, MAF becomes more likely cause. If symptoms still present, MAF less likely to be the cause. Be sure to drive car a while to give ECU time to adapt to absence of MAF input to unlearn possibly erroneous fuel mapping resuting from bad input from MAF.

Driving with MAF disconnected may result in check engine coming on, though, so you might want to consider buying an OBD II code reader/data viewer that provides you a means to not only read codes, but to clear them. Data viewing is nice cause it lets you view engine sensor data in real time which can help you track down cause of symptoms.

Which could be a bad coolant sensor or air temperature sensor (in the MAF). Either one delivering the wrong temperature reading can result in the engine running wrong cause the engine controller of course has the wrong temperature to base its fueling and ignition timing choices upon.

Be sure oil filler tube cap on tight and not leaking.

If you enable boost display does engine still make boost? No need to try to drive boost gage to max boost but a good press of the gas pedal in a higher gear with engine up to temp should see some boost and it is should persist a moment or two.

And always if symptoms get worse, if engine starts smoking, idle starts moving up and down -- not much but is no longer as steady as it once was -- shut off engine first and ask questions later, after you have car flat bedded to dealer for professional diagnosis.

Sincerely,

Macster.

 

vwow, Macster, thanks a lot for your reply!
after I parked the car this morning, I decided to take it to the dealer but since its sunday I would have to leave it there (the car is still under CPO warranty). I asked someone to follow me to the dealer so I could drop the car, so when I start the car and start driving she ran perfectly, no hesitation, perfect idle, she pulled all the way up tp redline full boost with no issues at all, so I decided to drive back home and maybe try to fix it myself or take her in person to the dealer(which I hate doing) during the week. Here in MD the weather has been crazy, this morning when I took her our it was 30F, the second time (when I was taking her to the dealer) it was 50F, so it seems like the car didnt like the cold temps, or at least huge delta Ts.
Thanks for your help

Turbomark: does this haped everytime you fill up?!?!

 

Sounds like there's a temp sensor that's delivering false or incorrect info and its failure point is between/betwixt 30F and 50F. Or the Ecu is able to deal with a smaller error at the warmer temperature.

Why not take the car to the dealer? It is under warranty after all.

However, before you head off, what you want to do is learn how to reproduce the symptom without fail. If you take car to dealership and its warm like it was the day you headed out service will start engine and drive car and will not see any untoward behavior. For better or worse this puts you in a bad light and you'll have less credibility the next time.

If symptom only present when temperature is cold, say at or below 30F be sure you pay attention to the weather forecast and the temperatures and arrange to take car in day before and instruct dealership to leave car out in the cold and start it cold first thing the next morning.

Another thing you can try is to try to follow the same steps you followed the other day. Fill up gas tank and then do what ever you did afterwards. The closer to the same temperature the better, but you may not be able to arrange it of course.

Sincerely,

Macster.