SSST

The last week, when I started up one morning, everything was fine. Car started right up and idle was smooth and even. Let out about half clutch to get it out of the garage, and then pushed the clutch in and let it coast down the driveway (about 30 yards). At that point the revs started cycling steadily between 900 and 1100 rpm.

I get to the bottom of the driveway and I have to brake and ease at an angle down the sharp incline where the driveway meets the street. Let out the clutch a bit to get it into the street.

When I push the clutch back in, no more reving. Shift in to 1st and off I go. No problems, no lights, power is normal, guages are normal. I forget about it.

This morning. The exact same thing happens again. It doesn't do it at startup. Only once I get the car moving and only as long as it takes me to get down the driveway. After that, everything is normal.

Any ideas?

Kevin

My money is on your MAF, because the cold start fueling is running without O2 control.

Don't clean, replace... If you engine starts to die, as you back out of the driveway or stalls rolling into lights>> fuel pump is suspect.

When have you done your plugs..

raineycd

That and do a system leak test to find any boost or vac line leaks.

SSST

No issues this morning. Everything was normal. The only difference was that I filled up the tank last night, but bad gas would have resulted in more consistent odd behavior or loss of power.

I also checked and it hasn't thrown any codes. I'll just keep an eye on it and see if it happens again or becomes more consistent. The weird part os it's only happened twice and only while coasting backward about 30 yards down my driveway.

Macster

What was the fuel level when the symptoms appeared? Near half empty? If so could be a fuel siphon problem.

Sincerely,

Macster.

SSST

Probably close to a full tank the first time it did it, so I don't think that is the problem.

Kevinmacd

Unless there is a little water in the tank from all this ethanol stored in the ground. Going backwards incline puts the water close to the pickup. It's just a thought but hopefully it doesn't pop it's head up anymore!

SSST

I thought of that. It had been sitting for a couple of days both times.

Hopefully that's it. Probably need to top off the tank before it sits.

Macster

I do not believe water is the cause of the symptom.

While the fuel filter of the Turbo maybe different my experience with other vehicles is if water hits the fuel filter element (which is paper) the paper element simply absorbs the water and this blocks fuel flow. When this happened to one of my vehicles -- making a sharp turn with a very low fuel level (in a metal tank no less) -- the engine stopped like a switch had been flipped. I could see inside the filter and spotted some rusty drops of water. I removed the filter and blew it out and put the filter back and the engine fired right up.

Futhermore, when my 02 Boxster's fuel pump failed and was replaced the tech found no signs of any water in the tank and the tank has had about 8000+ gallons of gas go through it and save for a few times I've used a bottle or two of Techron I've never added any fuel additives to the tank that specifically are intended to address water in the fuel tank.

The fuel pump sits very close to the bottom of the tank so if there were any water in the tank the filter element and the 'stuff' caught in the fuel filter in the tank (which is the fuel pump housing and its fine (very fine) mesh) would have shown signs of being wet at various times. There was no sign of this. The tech told me the bottom of the tank was free of any signs of water and the amount of trash in the tank was quite low. The fuel filter mesh had some particulate matter 'trapped' in the mesh but the matter looked as if it had never been subjected to any water.

So, not water is my opinion.

But it could have been the gas stratified some and the ethanol and gasoline separated to some degree and it is entirely possible the fuel pump ingested a bit of gas that was more than a few percent of ethanol.

Now, if the Turbo's fuel pump works any way close to the one in the Boxster, there is some agitation of the fuel from the pump.

In fact the Turbo fuel pump may agitate the gas even more than other Porsche fuel pumps since in the Turbo the fuel supply system relies upon a fuel siphon to siphon fuel out of one of the two saddles into the one with the fuel pickup.

Anyhow, my Boxster's fuel pump has a bypass that reroutes some fuel around the pump and out again to cool the pump and this rerouted fuel works to 'stir' up the fuel thus this works to remix the ethanol and gasoline.

In the case of your car, though, it is not hard to imagine though that if the car sits long enough unused and if the gasoline gets stale (and depending upon where you bought the gas it may have been stale to begin with) this might result in a much more severe degree of stratification of the ethanol and gasoline. If so then shortly after engine start there might be a window of opportunity during which some gasoline with more ethanol than the engine can tolerate was ingested by the pump and fed to the injectors and the result is the behavior you noted.

Anyhow, you can keep the fuel level up or down, but I prefer for longer periods of inactivity to keep the fuel level close to full to keep the fuel pump and fuel lines and the rest of the in tank hardware submerged under gasoline.

Also, you might consider adding a fuel additive designed to help gas and ethanol remain blended and which helps combat stale gas until this tank of gas is used up.

Be sure you buy from a busy station to avoid getting gas that might have gone stale. With high gas prices many owners of cars that use premium gas cut back on and premium gas can sit in the tank at the station along time then a Porsche owner comes along and gets stale gas.

(Medium octane grades of gas are 'blended' at the station by combining gas from the premium storage tank and the regular storage tank but even so the amount of premium gas used is of course half what would be used if the car was filled with premium.)

Sincerely,

Macster.

SSST

Thanks macster. There are a lot of cars that use premium in my neighborhood and the station I use (Chevron) sells lots of the stuff. I will watch the tank level though.

Other than these two incidences, the car is running brilliantly.

Macster

Well, as long as the car runs ok then you can attribute the episode to a glitch.

If there's anything really wrong -- and I dont' really think there is -- it will make itself known in due time.

As I mentioned some time ago (back in Feb.) my Turbo generated a check engine light and the codes were misfires. (The car had sat out overnight in a motel parking lot in heavy rain.)

Save for a bit of rough running at engine start during which the check engine light came on just a moment or two after the engine settled into its characteristic idle and afterwards its behavior was as before this 'glitch': impeccable.

I checked in with the techs at my local dealer and was advised to clear the codes and continue to drive the car. If the coils or something else was the cause of the misfires the check engine light would come back on.

I followed the advice, even leaving the car out in the rain once or twice and treating it to a through soaking when I washed the car and the misfires have not returned. That was probably 10K miles or more ago.

Sincerely,

Macster.

Kevinmacd

In ethanol fuel, you get phase seperated alcohol. You get a degradation of blended fule since alcohol absorbed water.

SSST

It still hasn't happened again, but it's going to be sitting until Friday, so I may get another read on it then.