O2 sensor, idle problems and air flow sensor?
03-05-2002, 10:53 PM
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O2 sensor, idle problems and air flow sensor?
After buying a 93 C4 a year ago and driving it daily with no problems I finally took it to a dealer for a 35k mile service (I got it with 18k on it!). Straightforward and friendly - but as I drove away the engine light came on intermittently for several minutes at a time. Drove 20 miles to work, car very hard to start when I left work later. Idle overshot, oscillated 3-4 times and died whenever car stopped. Checked DME code (I dug this up on the web when I realized there was a problem); it was 1_24 = O2 sensor. Took the car back to the dealer, they reported an open circuit on the sensor (does this mean unconnected?) and replaced the sensor. No charge for labor since I argued that the sensor got screwed up during removal for the valve adjustment, but I was willing to pay for a new sensor. Ten days later after daily 25+25 mile commutes and a 5+5 hour round trip from Boston to Maine, the car was very hard to start one cold evening after work (25 deg F). Idle was completely missing - I had to keep throttle down to keep car from dying. Engine light on. Drove 20 miles on expressway, light went off and idle returned. When I got home I checked the DME code and got 1_22 = idle speed control. Dropped car off at dealer this morning; their diagnosis is to replace air flow sensor (not the error code I saw!) for $800+. I told them to hold off, and contacted an independent mechanic to take it to next week. I will pick up the car tomorrow.
After spending the evening looking over recent posts I have become even more sceptical than I was before. It seems plausible that the idle problem is with the idle microswitch, which failed to close but eventually warmed up or jiggled loose after driving. After the service and oil change I had noted that the oil level was high - the needle was pegged at the top, although the dipstick was right on the top mark, and not noticeably over. Is it possible that it was overfilled and excess oil has caused the idle switch to stick? (not to mention possible effects the airflow sensor).
In any event I would appreciate hearing some other opinions and getting some advice from those more knowlegable and experienced than I am. This is my fourth daily driver, starting with a 356C in 1964, a 1970 911T (the last one to see a dealer in the mid 70s), and a 1979 911SC before I got the 964. All have been solid and reliable, although things have broken and worn out as expected. But this rash of problems immediately after servicing is puzzling. I won't have time to poke around much myself until the weekend.
Thanks for all the info I already found on the list - you all have been doing a great job.!
Rick
After spending the evening looking over recent posts I have become even more sceptical than I was before. It seems plausible that the idle problem is with the idle microswitch, which failed to close but eventually warmed up or jiggled loose after driving. After the service and oil change I had noted that the oil level was high - the needle was pegged at the top, although the dipstick was right on the top mark, and not noticeably over. Is it possible that it was overfilled and excess oil has caused the idle switch to stick? (not to mention possible effects the airflow sensor).
In any event I would appreciate hearing some other opinions and getting some advice from those more knowlegable and experienced than I am. This is my fourth daily driver, starting with a 356C in 1964, a 1970 911T (the last one to see a dealer in the mid 70s), and a 1979 911SC before I got the 964. All have been solid and reliable, although things have broken and worn out as expected. But this rash of problems immediately after servicing is puzzling. I won't have time to poke around much myself until the weekend.
Thanks for all the info I already found on the list - you all have been doing a great job.!
Rick
03-06-2002, 03:17 AM
#2
Rick:
Your car is pushing 10 years old, and the previous cars you've owned (Porsches anyway) really didn't have as many sensors (in some cases, maybe none!). Things age and wear out. An overfill of oil may be responsible for your idle problem, but I don't think it's likely it's causing your sensor problem (it's probably a long shot, but it could be possible). I think it's probably just bad luck.
You need to make sure you're reading the codes properly. I responded to your quotes in a previous post about the "_" you have identified. All the codes will be four digits (except the 1500 which means all is well and means you get a "1" for DME id, then 5 flashes followed by two "non-flashes" so all you see is one flash, followed by five flashes, and this repeats itself). All other codes will be four digits. If you see the _ as a pause or something, then you're probably misreading the codes. The "_" should be one or two flashes, with a single flash meaning a continuous problem and two flashes meaning an intermittent problem. The DME will always start off reporting a single flash for the DME id, then one or two flashes to indicate continuous or intermittent problems respectively, followed by another two sets of flashes that will identify the source.
To make matters worse, the possible cause of the problem you're referencing (idle microswitch) is code 12, so it would either show up as a 1-1-1-2 flash sequence or a 1-2-1-2 sequence. The DME will also store codes sequentially as they occur, so in the event that you had two faults occur over time (let's say the idle microswitch failed, followed by the O2 sensor, both with INTERMITTENT failures, then the codes would read 1-2-1-2 followed by 1-2-2-4 before repeating).
Maybe you know all of this already and if so, I appologize, but there's probably someone out there who isn't familiar with this stuff so I though I would spell it out in detail...plus I have a lot of time on my hands tonight
FWIW Porsche used the "_" in some of there descriptions of the engine codes, so that's probably where it came from.
Hope this helps <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Bill Wagner
Your car is pushing 10 years old, and the previous cars you've owned (Porsches anyway) really didn't have as many sensors (in some cases, maybe none!). Things age and wear out. An overfill of oil may be responsible for your idle problem, but I don't think it's likely it's causing your sensor problem (it's probably a long shot, but it could be possible). I think it's probably just bad luck.
You need to make sure you're reading the codes properly. I responded to your quotes in a previous post about the "_" you have identified. All the codes will be four digits (except the 1500 which means all is well and means you get a "1" for DME id, then 5 flashes followed by two "non-flashes" so all you see is one flash, followed by five flashes, and this repeats itself). All other codes will be four digits. If you see the _ as a pause or something, then you're probably misreading the codes. The "_" should be one or two flashes, with a single flash meaning a continuous problem and two flashes meaning an intermittent problem. The DME will always start off reporting a single flash for the DME id, then one or two flashes to indicate continuous or intermittent problems respectively, followed by another two sets of flashes that will identify the source.
To make matters worse, the possible cause of the problem you're referencing (idle microswitch) is code 12, so it would either show up as a 1-1-1-2 flash sequence or a 1-2-1-2 sequence. The DME will also store codes sequentially as they occur, so in the event that you had two faults occur over time (let's say the idle microswitch failed, followed by the O2 sensor, both with INTERMITTENT failures, then the codes would read 1-2-1-2 followed by 1-2-2-4 before repeating).
Maybe you know all of this already and if so, I appologize, but there's probably someone out there who isn't familiar with this stuff so I though I would spell it out in detail...plus I have a lot of time on my hands tonight
FWIW Porsche used the "_" in some of there descriptions of the engine codes, so that's probably where it came from.
Hope this helps <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Bill Wagner
03-06-2002, 04:38 AM
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Dear Rick,
Unfortunately there are 55 pins on a DME connector and a failure on each one can cause idle problems.
From your post I feel that you are getting unrelaible data in the fault codes because the whole system is sort of failing and the DME cannot genuinely work out what is happening. This is an inbuilt problem with these diagnostic systems of the 1980s and 1990s.
Having no idle at all indicates a failed idle microswitch first. If this microswitch is not being made when you take your foot off the pedal the idle speed control valve will not open to its idle position and the 964 will stall. Failure of the switch can also be an adjustment or mechanical problem.This can also fire up an air flow sensor fail because there is no airflow if you know what I mean.
So I would start with the microswitch circuit.
Overfilling of oil is a major problem and can trash your air flow sensor. It is easy to check. Pull of the airbox cover and filter, put your hand inside of the airbox and check for oil residue.
I would also check the dipstick. If the dipstick is not seated and correctly sealed, guess what, idle problems and stalling.
It is a matter of basic troublehsooting. Start cheap and then get expensive.
Some of these things you can check yourself like the microswitches. You may just have a bad connector. Good luck. One last question. Was the DME reset return to service drive carried out. It could be as simple as the DME memory was erased and a proper test drive was not carried out. Not the first time this has happened.
Ciao,
Adrian
911C4
PS: Open circuit O2 sensor will not normally cause idle problems. If it fails whilst you are in closed loop it will fire up a failure this is true and you will be switched to emergency mode. Stalling in this mode is not uncommon. However next time you start up you will be in open loop mode and stay there.
Unfortunately there are 55 pins on a DME connector and a failure on each one can cause idle problems.
From your post I feel that you are getting unrelaible data in the fault codes because the whole system is sort of failing and the DME cannot genuinely work out what is happening. This is an inbuilt problem with these diagnostic systems of the 1980s and 1990s.
Having no idle at all indicates a failed idle microswitch first. If this microswitch is not being made when you take your foot off the pedal the idle speed control valve will not open to its idle position and the 964 will stall. Failure of the switch can also be an adjustment or mechanical problem.This can also fire up an air flow sensor fail because there is no airflow if you know what I mean.
So I would start with the microswitch circuit.
Overfilling of oil is a major problem and can trash your air flow sensor. It is easy to check. Pull of the airbox cover and filter, put your hand inside of the airbox and check for oil residue.
I would also check the dipstick. If the dipstick is not seated and correctly sealed, guess what, idle problems and stalling.
It is a matter of basic troublehsooting. Start cheap and then get expensive.
Some of these things you can check yourself like the microswitches. You may just have a bad connector. Good luck. One last question. Was the DME reset return to service drive carried out. It could be as simple as the DME memory was erased and a proper test drive was not carried out. Not the first time this has happened.
Ciao,
Adrian
911C4
PS: Open circuit O2 sensor will not normally cause idle problems. If it fails whilst you are in closed loop it will fire up a failure this is true and you will be switched to emergency mode. Stalling in this mode is not uncommon. However next time you start up you will be in open loop mode and stay there.
03-12-2002, 05:52 AM
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Dear John,
Only USA versions of the 964 were fitted with the check engine light system. ROW versions all need the Bosch Hammer to read out fault codes or the 9268 Led Flasher test set to see the flashing codes,
Ciao,
Adrian
911C4
PS: This difference was not rectified until the 996 series as I found out yesterday. The 993s have different DMEs with different capabilities as well.
Only USA versions of the 964 were fitted with the check engine light system. ROW versions all need the Bosch Hammer to read out fault codes or the 9268 Led Flasher test set to see the flashing codes,
Ciao,
Adrian
911C4
PS: This difference was not rectified until the 996 series as I found out yesterday. The 993s have different DMEs with different capabilities as well.
