autobonrun

I'm wondering is there a somewhat general consensus on this board on which sensors can over time degrade in performance and impact the TT's performance without outright failing and tripping a CEL? I ask because it is generally accepted on my BMW board that hall effect cam position sensors for example can do this on an M5. In fact, replacing all 4 of these sensors on my M5 smoothed out the idle and eliminated the jerkiness I felt when I first started out in the mornings with a cold engine.

I only have a bit less than 25k miles on this TT, but have decided to take it in for it's 30k mile maintenance within the next month or so. I'm doing it because the car did not have the maintenance history I like to see on a used car so I want to establish a baseline by knowing what's been done. I'm not one to throw parts at non existent problems but would like to get this car sorted out to my satisfaction quickly. By sorted out I mean I have knowledge of the maintenance done and the car is running well consistently.

In addition to the 30k mile maintenance items, I was thinking about replacing the MAF, O2 sensors, and coils as well. I've tried cleaning MAF's in the past and am not a big proponent of that method. I'm curious if you feel O2 sensors and coils on the TT can degrade in performance over time without actually tripping a CEL? What other important performance sensors can also degrade over time on the TT?

rmc1148

I personally believe spark plugs- O2 sensors do not degrade over time to the point of needing to be replaced prematurely. You my pick up a bit of performance by replacing these parts early you may not. The MAF again at your mileage is probably fine. The coils can be checked for cracks. I replace o2 sensors at 50k mainly because I'm ****. You will get a lot of opinions and one really long winded one= use common sense. If it makes you feel better about your car replace parts mentioned its not expensive and easy to do yourself.

Kevin

Plugs might not degrade, but the electrode gap increases due to erosion. On can remove your plugs and clean then and regap/reinstall them.. But with the cost of plugs being cheaper than the labor it's easier to install new.

The MAF sensor degrade over time due to the oxide that build up over time. Resistance increases and voltage sent to the ECU are distorted. I suggest changing the MAF every 4 years.. Depending on miles driven.

Bosch recommends O2's being changed every 50K or 10 years of service.. I think the post CAT O2's can be run longer..

autobonrun

Thanks for the input. I'll get the plugs changed now only because that's part of the 30k mile checkup. I'll hold off on the O2 sensors. As far as the MAF, I will go ahead with that replacement but delay it a few weeks after the 30k mile tune. I always like to replace parts separately if I can easily access them. That's the only way I can tell what part had what effect on the car's performance.

What I'm really wondering are there other type of sensors on the TT that can degrade? Are there cam position sensors on the TT that you guys ever change out? I'm thinking for example of a throttle position sensor. I assume the TT uses one. What made me think of it is I notice a slight hesitation intermittently if I try to hold the TT at a constant speed with the throttle; for example there's a momentary bobble at 70 mph using the accelerator pedal. I did read something on this board about this happening at some RPM's. Strangely, if I use cruise control to hold the same speed, there's no hesitation. It kind of leads me to think it's an issue with me getting use to the throttle response from the pedal.

Just curious.

"02996ttx50

the cps ( hall effect ) sensor in my car according to my handheld code reader ( p0342 ) says my bank one cps is sketchy but i have not ONE cel since fully charging and keeping on the ctek my barely 1 yr old battery. batteries are the real weak spot in these !

add: "cleaning"? mafs is total BS and a fools game. works for some.. for a minute lol

TeCKis300

I'd definitely add the O2 sensors to this list, especially the primary sensors.

It's not so much a vulnerability in the Porsche, but an inherent quality of all O2 sensors. Their response gradually slows down over their useful life until it no longer meets a predetermined threshold at which point it will trip a check engine light. O2 sensors are sensitive to heat and high performance cars generate more of it, hence they may degrade faster especially in a modded/tuned car that might be tuned to run leaner (i.e. hotter).

rmc1148

Hold onto your used but good MAF as it could come in handy later for trouble shooting.

Kevinmacd

When you do plugs change to new coils. Also check the cam solenoid brackets for cracks! If I am not mistaken I think the new coils available are 997 coils that are an upgrade form the original 996 coils. Maybe someone can verify that. I know the coils I replaced had 997 in the part number.

"02996ttx50

I change plugs to coils at a 2 to 1 ratio, since plugs burnout faster that coils do. of that I am certain.

the 997 part number for the coils ( supercedes ) the 996 part number but that has nothing to do with an upgraded/improved part per se, but rather the older part number with the "996" designation is no longer manufactured, hence the 997 part# which is suitable for both cars. this is same for bosch or beru, though I am only familiar with the bosch part # from my last replacement.

but again, plugs two to one to coils as a change ratio is NOT a mistake on a TUNED mid level ( 500/600whp ) modded car.

Kevinmacd

Thought the upgrade was in the epoxy material used to prevent any cracking. So I was told.

"02996ttx50

good advice. just don't anyone think that "cleaning" them is worth a damn lol

oh, I know someone's experience will be contrary to that, such is the nature of i'net forums. mafs once dirty/fouled/fried need replacing with NEW bosch 996/986 part ending in '124-00 for the 996tt.

"02996ttx50

hmmm, could well be. I was told it was as I wrote. perhaps both are true.! but I promise we will see/hear of cracked 997 coils lol

Kevin

The new 997TT coils have been manufactured with different epoxy/plastic/assembly.. We are seeing the new 997TT coilpacks fail due to mileage and years of service. The 2 to 1 change ratio is a wise practice.

Cleaning a MAF is a worthless experiment.. Replace it with a Genuine Bosch unit that hasn't been tampered with. Make sure that you buy Genuine not a Cheap clone.. If it's selling for $150.00 it's a cheap clone..

Macster

General consensus? Here? You have to be kidding.

But there are plenty of opinions.

The DME constantly "tests" various sensors -- for instance the O2 sensors -- to verify they are responding in an acceptable fashion.

As long as the CEL is dark and there are no pending O2 sensor codes, and the engine is not exhibiting any signs of issues one can assume the sensors while possibly operating at less than brand new out of the box levels of performance are still operating at a sufficiently high level to not materially affect the engine and its performance.

You have to be careful you do not attribute to the O2 sensors degradation that is really due to the converters. The DME uses the #2 sensors to monitor converter performance and if it doesn't get the performance it expects it can change fueling. This can show up at the #1 sensor and one can look at the readings, the long term fuel trims, and see the DME is making or has made some adjustment and possible mis-diagnose this due to sensor degradation when the problem is with the converter.

Since the O2 sensors play a critical role in engine fueling and emissions compliance and the performance of the converters which are I might add covered by a federally mandated warranty, automakers are pretty good about flagging a problem that can impact the converters. This includes a problem with the sensors.

(The same applies to the knock sensors, which are checked for proper operation.)

This is the long way of saying if there is no error code (active or pending) there is no problem.

In this same vein, if the sensors of the two different banks are providing close to the same reading there is no problem.

As for plugs, I think Kevin is spot on with his comments. While one can remove and clean and re-gap the old plugs, my preference is to just replace the plugs. I do not like to reuse/reinstall "old" plugs for reasons I'll not go into here. I treat plugs as an install once service item and if a plug has to come out it gets replaced. I might add with my cars no plug has ever needed come out at any time before its scheduled replacement interval.

Coils are tricky. Their service life is somewhat affected by where one lives/drives. I recall early on after buying my Boxster encountering a number of posts on the UK boards about bad coils at miles way under what miles my Boxster had accumulated. The "difference" was I live and drive in a reasonably dry climate while of course UK drivers it is just the opposite.

There are some who believe when the plugs are changed the coils should be changed. My philosophy is to certainly carefully inspect each coil and replace those that show signs of degradation. In fact I would if all the coils were the same age and "old" that if just one coil showed signs of needing replacement I'd just do the lot of them.

Even if the coils look just fine, if the engine misfires at any time even once in a great while during a cold and damp start I'd replace the coils. (I failed to heed my own advice but I will say the engine never misfires at any other time and because of where i live cold/damp starts are very rare, courtesy of the "drought", I can't recall when the engine last misfired. But having new coils installed is on my list of to do items.)

I have never found a MAF that needed cleaning. If the stock air filtration system is working properly the MAF does not need any cleaning. If it does then the bigger problem is engine is not getting properly filtered air.

The DME can flag a bad MAF rather easily so absent any signs of a bad MAF, I don't even bother this thing. The one in my Turbo has covered 131K miles and I'm leaving it in service (and uncleaned) for as long as it continues to operate with no issues.

A misbehaving coolant temperature sensor is a possibility. So far the Boxster and Turbo coolant sensors have remained in good working order. I had a VW Golf TDI that was acting up and for some reason I attributed this to the coolant sensor and my monitoring of this sensor's output in real time using an OBD2 code reader/data viewer confirmed my suspicion and i had the dealer replace this sensor and the symptoms -- I forget them now -- went away. There never was any CEL or error codes.

In any car from my 1996 Mustang GT to present I've never had a cam shaft or crankshaft position sensor fail or degrade to point there was anything obviously wrong.

Occasionally the Mustang produced an error code that was camshaft position sensor related -- I forget the code now -- and based on my history with the car I suspected just a connector was at fault and finally I went in and found this connector and disconnected it and reconnected it -- as far as I could tell the connection was ok -- and the error never returned. I believe the problem arose from surface corrosion at the connector interfering with the signal from the sensor.

The only thing in this area that has gone wrong is my Boxster's passenger side VarioCam solenoid/actuator went bad. The sensor was just fine.

Of course, cars are different and a sensor on my car that has lasted nearly 300K miles may have a much shorter life in your car. But absent any clear indication of a problem I would not resort to premature/preventative replacement.

Otherwise based on this every sensor and solenoid and actuator and tensioner would be a candidate for premature/preventative replacement and that's a big expense. And even after one does this he still has to consider the replacement hardware could suffer a premature degradation or outright failure and one has to at some level keep an eye out for any signs of degradation or failure. So even with all these items getting replaced one buys no real release from taking an active role in monitoring at some level the engine and its population of sensors and the engine and sensor performance.

rmc1148

And there it is.