Roger Johnsen

I just recently (in the last few days) got my '04 TT as a surprise. The car has been great but recently my wife took it and the "check engine" light came on. She said it just happened - no events or details to offer. Has anyone heard of this? My search turned up MAF sensors and the owner's manual indicates a loose gas cap could cause this. The gas cap is tight so I don't think it's the latter. Anyway - I'll take it to the dealer to get it checked out...

Barn996

Get yourself a code reader that will not only tell you the fault codes, but erase them as well. GL

adam_

Do yourself a favor and find a good indy...

But you really need to get a code pulled... free at some auto parts places. There can be 100 things that can trip a light.

How many miles? Maintenance history?

Oh, re: dealers...I knew a guy that took it in for a CEL, dealer said, "Probably covered by your CPO, but I need to put $280 as the estimate to cover 2 hours".

Picks it up, SA says there was a gas tank evap leak, so we did a complete diagnostic, but it passed, so we assume it must have been a loose cap... took two hours, and CPO didn't cover it since there was no actual failure"

My point being it can get mighty expensive to allow dealers to poke around..

GL

A

Roger Johnsen

Thanks for the advice - I'll look into getting a code reader. I just turned 30K miles on the car - took it to Porsche of North Scottsdale for a 30K mile service and to check the car over before I bought it.

doubleurx

And check your gas cap!

Roger Johnsen

I borrowed a friend's code reader and it reported "P0300" as the diagnostic code. A quick search online provided the following:

A random misfire code can be set on newer vehicles with OBD II onboard diagnostics when multiple misfires occur randomly in multiple cylinders. The cause is typically a vacuum leak in the intake manifold, throttle body or vacuum plumbing, a defective Exhaust Gas Recirculation (EGR) valve that is leaking exhaust into the intake manifold, or even bad gasoline. Less common causes include bad spark plug wires, worn or fouled spark plugs, a weak ignition coil, dirty fuel injectors, low fuel pressure, or weak valve springs. If a misfire is occurring in only one or two cylinders, you will usually find a misfire code for that specific cylinder rather than a random misfire code.

Hopefully it's just bad gasoline but will have it checked and go from there. Thanks for the replies!

ECB

I think that's the 'Don't let your wife drive' code.

adam_

"Bad Gasoline"???

That is almost an urban myth. It is exceedingly rare.

See what comes back. Were the spare plugs changed?

A

porka

could be caused by a misfire if it was real low on gas!

Roger Johnsen

I cleared the diagnostic code and took it out for a drive. Filled up the gas and went ballistic. No more codes reported. She did manage to stall it out a couple of times so maybe that was related. She's taking my 986 S so hopefully that will keep her from driving the new toy...

Macster

My info is the Ecu will not record a misfire (lean misfire anyway) if the gas tank level is low, real low. And by this I think the low fuel level warning light needs to be on.

If you tell me the vehicle is equipped with a stick it could then be caused by starting the car out at too low an rpm. I've seen women (and some men) get into cars and to get the car moving from a stop just sort of dump the clutch at engine idle and then feed the engine some throttle and the engine's protesting some before it picks up rpms.

That no specific cylinder misfire codes were recorded suggests to me this is what happened, unless of course the car's equipped with a Tip.

Bad gas gets blamed and while it is not true in every case bad gas does exist.

It can arise in several ways:

One is someone just fills up at some no name off brand station that while it has 'premium' gas the gas meets the premium requirements, barely.

Also, gasoline is pumped through pipelines. A batch of regular gas is put into the pipeline, then a batch of premium, then another batch of regular and the whole slug is pumped through the pipeline. Surprisingly, there is not that much blending/mixing. But there is some. At the receiving end the various batches are removed from the pipe. The trick is to take the premium from the sweetest area of the pipe's contents. There is a chance for error, miscalculation, and of course if say 1M gallons of premium was put into the pipe as close to 1M gallons of premium that can be removed means profits are highest. So there's some incentive to cut this close. Guess which stations might get the premium gas that is closest to the sandwiching batches of regular?

Two is the gas is good, started out good, but has sat in a storage tank at the gas station and has grown stale. A gasoline test in Evo magazine a few years ago (Evo's a UK published car magazine) found stale gas to be real. The mag recommended buying from a busy station. There are two benefits: 1) the gas is not likely to be stale cause the tanks are replenished frequently. (I've found some busy stations get refills up to 4 times a day.) 2) A busy station usually has the lowest prices.

Three is old gas sits in a car's tank for weeks which of course allows the gas to grow ever staler.

And four is the gas fresh (or not) but is not the right blend for the climate conditions. This happens most often in the fall and spring. Someone fills up with 'summer' gas and then a month passes and the cold sets in. The gas does not have the proper blend for the colder temps and the engine suffers a bit for it. Or someone fills up with 'winter' blend gas in early spring and then an unexpected hot spell comes in and this can cause problems.

Lastly, I do not know the history of the car, but it might benefit from a treatment of Techron, maybe two. Fuel system deposits and combustion chamber deposits can interfere with the proper combustion and misfires of the sort responsbile for that P0300 can arise.

Sincerely,

Macster.

adam_

Lugging/ almost stalling at low rpm at start can cause a CEL? Thats a first.

Bad gas probably exists and hundreds of people would be affected- and once in your tank you will have repeated issues until diluted or drained.

But so many people, at a loss to understand cars, just think 'well, what did I do different?' and the answer is 'filled the tank'. Someone says bad gas and there you go...

So how can someone get a tank of "bad gas" that is OK for say 100, 200 miles, then just "goes bad" and causes a single P0030 misfire?



OP has 30k miles and we don't know if the plugs were changed.

Anyway, not much to do until the code comes back repeatedly. Maybe even cylinder specific, then you have more data.

Macster

Since the symptoms appeared with a change of a driver the possibility the driver drove the car differently and contributed to the symptoms is always a possibility. And many drivers based on my observation tend to lug these cars. But the odds are not in favor of this being the cause.

Sincerely,

Macster.

Roger Johnsen

I was hoping the problem was the wife driving and would simply "go away" but looks like it's not that easy. I went to take the car for a drive and had the CEL go on again with P0300 and P0306. This happened when the car had just been started and was running at idle in my garage. I've noticed it seems to be running a little "rough" over the past couple of days as well. (Not exactly mechanic speak but the passenger seat back was shaking back and forth when I was at idle.) I've gone through at least three tanks of gas since the first code was triggered / CEL came on so would rule out bad gas theory.

The car is just over 33k miles now. The 30k mile service was performed just under 29K miles by the dealership prior to my purchase. The invoice lists a quantity of 6 spark plugs among other items from that service. (Part # 999-170-195-90) I should also add the dealership did a full inspection on the car during the 30K service and only noted the front brakes should be checked on the next visit.

ms4cd

The seat shaking is almost normal. My 996 does the same thing. I would be interested as to the final outcome of this problem.

My car was purchased used, initially under hard acceleration I felt stuttering and boost loss. Random but, I did not have a CED even under those conditions.

Spark-plug change did the trick. No more stuttering. I see you have done that, if you do not mind me asking what dealer did the car come from?