AOS failure on Sunday

My 2002 2.7 base with 207K still my daily driver. Starting to have an issue with low speed lunging/surging going up a grade a low rpms (tiptronic). I am wondering if this is a transmission problem, and have been waiting for it to get worse before I take it to my local indy. If I downshift to increase rpm's, seems to go away. Any thoughts on what this could be?

BarryL
2002 2.7 Seal Grey Tip
Santa Cruz, CA

Does it also surge at idle speeds? If so, its probably an air leak.

Do you have any codes (including pending codes, which don't trigger the CEL)?

Tiptronic
MAF
Fuel delivery (clogged injectors, e.g.)

As I recommended in another thread, I would recommend running a bottle of Techron fuel system cleaner (not fuel injector cleaner) through the system and see if the problem gets better or goes away.

But before you go much further my recommendation is to have an experienced Porsche tech road test the car and advise you. He should be able to distinquish between a stumble/hesitation caused by the engine vs. one caused by a misbehaving Tip.

Assuming it is engine related, any pending error codes?

Hi Marc,

It's been a while since last service (9 months), about 40 k on spark plugs. Probably time to have my local Indy check it out. Thanks so much and I will post the out come. So great to have you still around on this board for invaluable source. Boxsterra too,

Barry

Coming back from golf up along the coast from Monterey. smoke began bellowing out my exhaust and I pulled over as soon as I could(about 30 sec). Engine lost power in vapor lock as I was coming to a stop. Flatbed tow to my local Indy. He will be working on it tomorrow but indicated total engine freeze up. He seemed confident he could drain oil out of the spark plugs holes and that it should be fine. Fingers crossed.

BarryL

My 2002 Boxster suffered something similar although at the hands of the tech when I had it in for what proved to be the first AOS replacement of 3 (so far).

The lock up occurred while the car was in for the AOS replacement. Not sure of the circumstances now. (I recall being told the lock up occurred during a compression test. A compression test was apparently "SOP" in these cases which is insane in my opinion.)

Apparently the lock up didn't do any harm. That was at around 80K miles and the engine has over 313K mile in total on it now and still runs fine. And it has suffered 2 more AOS failures both which ended in the engine smoking like crazy but in which the engine was shut off and not run anymore until after the AOS was replaced.

When you get your car back the engine will probably smoke upon the 1st and maybe the new few subsequent starts especially if the engine is not run much after the AOS was replaced or you don't run the engine much when you drive it. It takes time for the oil that has gotten into the intake due to the failed AOS to work its way out of the engine.

You want to try to run the engine a while to get the engine fully up to temperature and ideally the intake warm as it can be which means driving the car around town with its stop and go driving which has the intake as warm as it can be.

The engine may trip a check engine light so don't be too surprised if this occurrs. The odds are the light arises from the oiling the engine was subjected to and the oil in which is being worked out of the engine. So a read of the code or codes, a check for any pending codes, and after writing all these down just clearing the codes followed by a road test to see if the CEL comes back on is called for.

If you want a treatment of Techron could be called for. Get a bottle that treats 20 gallons and at the gas station shake the bottle then dump its contents in the gas tank followed by filling the gas tank with whatever premium gasoline you use then just driving the car. The Techron will remove any engine deposits -- those that have been accumulated from the recent "oiling" and any that were present before. The general rule is if you notice any improvement in how the engine runs to follow the 1st bottle with a 2nd bottle after the gas with the first bottle added is way down to say a quarter a tank. My advice would be to just plan on using two bottles -- one right after the other -- regardless.

After the last tank with Techron is down to 1/4 of a tank or so then plan on having the oil and filter replaced. The Techron in doing its job can add to the oil's contamination level and it is best to then remove this oil and the filter.

This will be my 4th AOS. Like in your case, my mechanic didn't expect there to be a problem in getting this cleared and back on the road. He said there is a lot of inaccurate hype on the internet that this type of event destroys engines. It came on so fast, without warning and I shut it down pretty soon, but not immediately as I was in on highway 1 coming up the coast and it took me 30 sec to find an place to safely pull over. Funny I was thinking it was about time to replace the AOS, but didn't act preemptively. He will be working on the car today.

BarryL

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BarryL
This will be my 4th AOS. Like in your case, my mechanic didn't expect there to be a problem in getting this cleared and back on the road. He said there is a lot of inaccurate hype on the internet that this type of event destroys engines. It came on so fast, without warning and I shut it down pretty soon, but not immediately as I was in on highway 1 coming up the coast and it took me 30 sec to find an place to safely pull over. Funny I was thinking it was about time to replace the AOS, but didn't act preemptively. He will be working on the car today.

BarryL

4?! Thought being on the 3rd replacement AOS (4 total) I was the record holder, but I guess not.

While it is not common for an engine to be destroyed there is the risk. I always caution owners that if an AOS is suspected don't delay in getting it diagnosed and if found to be bad replaced.

Oil removed from cylinders, new AOS, sparkplugs and oil/filter. My indy said to expect burn off of oil for awhile, and when I drove home from the shop, particularly on startup, quite a burn off. My indy is going on vacation and didn't have time to check out the low speed shudder issue I was having on this visit. The new spark plug replacement did not fix this. I will be taking it back in a couple weeks to address this and a slight grinding sound that he said he had heard that he needed more time to locate. Nice to have my car back, but will be better when I find out what else is going on.

BarryL '02 2.7 Seal Grey Tip 207K
Santa Cruz, CA

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BarryL
Oil removed from cylinders, new AOS, sparkplugs and oil/filter. My indy said to expect burn off of oil for awhile, and when I drove home from the shop, particularly on startup, quite a burn off. My indy is going on vacation and didn't have time to check out the low speed shudder issue I was having on this visit. The new spark plug replacement did not fix this. I will be taking it back in a couple weeks to address this and a slight grinding sound that he said he had heard that he needed more time to locate. Nice to have my car back, but will be better when I find out what else is going on.

Did the tech give you any feedback on the shudder issue? I would hate to advise you to try X or Y when the shuddering is clearly severe enough the car needs not to be driven and the car turned over to a professional tech for diagnosis.

If the shuddering is of a mild sort you can try a couple of things. First do an E-GAS calibration. Start with the ignition key off. Keep your foot off the gas pedal through the entire procedure. Turn the key to the on position and leave on for at least 60 seconds. (I use the dash digital clock as a minute timer.) After 60 seconds on turn the key off for at least 10 seconds. The next time the engine is started this is complete.

With my Boxster even given my usage -- 60 miles a day mostly high way miles (my work commute to/from work) -- a tank or two after I switched from Shell V-Power to Chevron Supreme the Boxster engine was running noticeably better particularly at low engine speeds.

A tank or two of Chevron gasoline might take too long. You can speed up this process by buying a bottle of Techron and adding this to the fuel tank then filling up the fuel tank. I get the black bottle that treats 20 gallons and just dump the entire bottle in even though the tank only holds 16.9 gallons of gasoline.

The recommendation is if you notice any improvement after burning through the tank of gasoline with Techron added to repeat the treatment with a 2nd bottle.

Afterwards my info is an oil/filter service is advised. The Techron as it works adds a bit oil contamination. While I don't bother to change the oil change schedule of either of my cars when I run Chevron gasoline if I use Techron out of a bottle I try to arrange to do this before an oil/filter service is due so that the last of the gasoline with the Techron added is nearly gone when I book the car in for an oil/filter service.

Be sure the engine air filter is ok. I recently changed mine after letting it go probably a couple of years (or more?) and I don't know how many miles. The filter was nearly covered with a layer of trash (leaves mostly) and the filter element folds were full of black dust (mostly tire dust I think). The filter was in such bad condition a change in the air filter had the engine running better. I've never experienced this before. I won't let the filter go again that's for sure.

The tech did not have any thoughts about the shuddering, only that if it were a transmission, it would be around $3500 to get a used one installed. The shuddering is not that bad at this point, more an irritation. I have been waiting for it to get worse before garaging the car. It almost feels like when you are stalling out a car with low rpm's, so if I keep the rpms up, seems to not to be an issue. I ordered some techtron, but my tech advised against using and he just changed out the oil, so I am in a quandry of what to do.... put the techtron in and then have to pour out brand new oil or just wait to have the tech check it out when I get my next appointment with him when he is back from vacation in three weeks. Air filter was just changed out. I will definitely try the E-GAS calibration.

As always Marc, thanks so much.

BarryL '02 2.7 Seal Grey Tip 207K
Santa Cruz, CA

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BarryL
The tech did not have any thoughts about the shuddering, only that if it were a transmission, it would be around $3500 to get a used one installed. The shuddering is not that bad at this point, more an irritation. I have been waiting for it to get worse before garaging the car. It almost feels like when you are stalling out a car with low rpm's, so if I keep the rpms up, seems to not to be an issue. I ordered some techtron, but my tech advised against using and he just changed out the oil, so I am in a quandry of what to do.... put the techtron in and then have to pour out brand new oil or just wait to have the tech check it out when I get my next appointment with him when he is back from vacation in three weeks. Air filter was just changed out. I will definitely try the E-GAS calibration.

As always Marc, thanks so much.

Well, I do not like to go against a professional tech, but Techron can be just what the doctor ordered. However, if the tech feels the shuddering is not engine related and the fact the oil should be changed afterwards and you have fresh oil in the engine this weighs on the side of not using Techron.

OTOH, $3500 (for a used Tip) to address the shuddering I'd want to be *darn* sure the Tip was the cause of the shuddering. I'd hate to spend $3500 on a Tip swap when a $20 bottle of Techron was all that was needed.

If the shuddering isn't bad enough to park the car and you can live with the behavior then wait until the tech returns and go from there.

After performing the E-GAS Calibration, seemed like the car ran smoother and shuttering was reduced somewhat. It is hard to describe the shuttering/hesitation...but at low speeds accelerating and more noticeably when going up an incline, the hesitation, shuttering seems to fluctulate, but the real shuttering occurs when I go over a roughness in the road or bump while accelerating, Kind of feels like the tires are out of balance, then discontinues as speed is increased. Appt with my indy in two weeks.

BarryL '02 2.7 Seal Grey Tip 207K
Santa Cruz, CA

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BarryL
After performing the E-GAS Calibration, seemed like the car ran smoother and shuttering was reduced somewhat. It is hard to describe the shuttering/hesitation...but at low speeds accelerating and more noticeably when going up an incline, the hesitation, shuttering seems to fluctulate, but the real shuttering occurs when I go over a roughness in the road or bump while accelerating, Kind of feels like the tires are out of balance, then discontinues as speed is increased. Appt with my indy in two weeks.

It is important to distinguish between "shuttering"/hesitation arising from the engine momentarily varying its output through no action on your part or from in your car's case the Tip varying the amount of torque it is transmitting.

Regardless I think you've done all you can do without getting your hands dirty. Best to just avoid using the car any and wait for your indy tech to return. If the symptoms arise from the Tip there's not much one can do. My sources tell me while a fluid change is often done in these cases the fluid change doesn't help and often seems to make things worse.

This leaves rebuilding the Tip or replacing it. Again relying upon my sources in many areas of the country there are shops that can rebuild one of these transmissions. The Tip or one very very similar to it is used in a number of other vehicles and because of the number of vehicles these shops are proficient at Tip rebuilding.

Replacement is another option. A new Tip I suspect is pretty expensive though I've never priced one but should come with a warranty. A used Tip is probably going to be less expensive but of course comes with some degree of risk as to its condition. And there is no warranty other than what the supplier of the used Tip might offer and I have no idea what if any warranty would be available.

Received a message from Mike who had a similar problem that ended up being the gas pedal potentiometer. In his case, it finally failed to the extent he had to have the car towed his mechanic. Some great information I can feed to my tech.

BarryL '02 2.7 Seal Grey Tip 207K
Santa Cruz, CA