hunting idle = bad O2 sensor?
04-25-2007, 11:54 PM
#1
Intermediate
Thread Starter
hunting idle = bad O2 sensor?
My name is Scott and I have a problem... and I have searched but not been able to find the solution...
My 90 C4 has had a hunting idle and sometimes stalls once it warms up since I bought it. I have replaced the plugs, replaced the caps and rotors, and set the valves. The problem has not gone away. The plugs all looked perfect and did not indicate a rich or lean running condition.
My thought it that since this only happens once the car warms up (and gets into closed loop mode), it is related to the O2 sensor - the fluctuation is possibly tied to the O2 sensor reading as is goes rich - lean - rich - lean...
What are your thoughts? Is it likely that my MAF is to blame? I remember that when my 944 did something similar, I took apart the MAF and cleaned the rheostat and it resolved the problem.
I don't want to spend $150 on an O2 sensor if I don't need one. I do have a durametric - will this help me to diagnose this problem?
My 90 C4 has had a hunting idle and sometimes stalls once it warms up since I bought it. I have replaced the plugs, replaced the caps and rotors, and set the valves. The problem has not gone away. The plugs all looked perfect and did not indicate a rich or lean running condition.
My thought it that since this only happens once the car warms up (and gets into closed loop mode), it is related to the O2 sensor - the fluctuation is possibly tied to the O2 sensor reading as is goes rich - lean - rich - lean...
What are your thoughts? Is it likely that my MAF is to blame? I remember that when my 944 did something similar, I took apart the MAF and cleaned the rheostat and it resolved the problem.
I don't want to spend $150 on an O2 sensor if I don't need one. I do have a durametric - will this help me to diagnose this problem?
04-26-2007, 09:05 AM
#3
Three Wheelin'
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Location: Halifax, Nova Scotia , Canada
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If the O2 sensor goes slow in operation that will give the problem. Try looking at the sensor signal with a multimeter and access operation speed ? Too slow and you need a new O2.
Geoff
Geoff
04-27-2007, 09:38 AM
#6
Do you have access to a Hammer?
If so, try an Idle Adaptation.
If so, try an Idle Adaptation.
Code:
Idle Adaptation
"What exactly is a 'system adaptation', and how is this different from a
battery disconnect reset of the DME?"
The 964 DME ECM has two adaptations:
1. Idle Adaptation -
On the earlier 3.2 DME system the idle was set by an external jumper
(caused open-loop idle) & then the idle screw was set to "center"
the idle RPM. On the 964, the Hammer causes the DME to go open-loop
and then causes the DME to "step" to the center for 880 RPMs. This
results in the closed-loop idle being "centered" for full
regulation.
2. CO adaptation -
The 964 DME ECM goes thru a CO adaptation whereby it runs open-loop
without the O2 sensor to "center" the CO setting to allow for small
variable changes, e.g. air leaks, fuel pressure, so in the
closed-loop mode the O2 system has optimal range (similar to TRA in
OBDII).
Both of the adaptation values are "lost" if the constant battery
voltage (pin 18) is removed. #1 above requires use of the Hammer. #2
occurs at initial running after battery voltage "loss".
"What happens with the idle in the case of a battery disconnect and no
hammer adaptation?"
The closed-loop still maintains the target idle of 880 RPMs but it's not
optimized for load changes, e.g. the A.C. compressor, the fans, the
lights, and the adapted CO setting.
04-27-2007, 01:41 PM
#7
Burning Brakes
Originally Posted by dfinnegan
Do you have access to a Hammer?
If so, try an Idle Adaptation.
If so, try an Idle Adaptation.
Code:
Idle Adaptation
"What exactly is a 'system adaptation', and how is this different from a
battery disconnect reset of the DME?"
The 964 DME ECM has two adaptations:
1. Idle Adaptation -
On the earlier 3.2 DME system the idle was set by an external jumper
(caused open-loop idle) & then the idle screw was set to "center"
the idle RPM. On the 964, the Hammer causes the DME to go open-loop
and then causes the DME to "step" to the center for 880 RPMs. This
results in the closed-loop idle being "centered" for full
regulation.
2. CO adaptation -
The 964 DME ECM goes thru a CO adaptation whereby it runs open-loop
without the O2 sensor to "center" the CO setting to allow for small
variable changes, e.g. air leaks, fuel pressure, so in the
closed-loop mode the O2 system has optimal range (similar to TRA in
OBDII).
Both of the adaptation values are "lost" if the constant battery
voltage (pin 18) is removed. #1 above requires use of the Hammer. #2
occurs at initial running after battery voltage "loss".
"What happens with the idle in the case of a battery disconnect and no
hammer adaptation?"
The closed-loop still maintains the target idle of 880 RPMs but it's not
optimized for load changes, e.g. the A.C. compressor, the fans, the
lights, and the adapted CO setting.
Trending Topics
04-29-2007, 11:48 PM
#10
Rennlist Member
I have a 1990 C4 and every time I disconnect the battery I have the same problem. My mechanic resets the computer with the hammer (adaptation) and the car is 100% - This happens every time.
04-30-2007, 10:04 PM
#11
Burning Brakes
Originally Posted by BaysideC4
I have a 1990 C4 and every time I disconnect the battery I have the same problem. My mechanic resets the computer with the hammer (adaptation) and the car is 100% - This happens every time.
05-01-2007, 07:21 AM
#12
Rennlist Member
No, there is not alternate method. I tried the spirited drive, etc.. Nothing works.
Instead of disconnecting my battery I now use a battery tender (plugs in the cigarette lighter) - I also store my car and use it a few times a month.
The Porsche battery tender is great , it keeps the battery at 100% and maintains it. no overcharging.
Instead of disconnecting my battery I now use a battery tender (plugs in the cigarette lighter) - I also store my car and use it a few times a month.
The Porsche battery tender is great , it keeps the battery at 100% and maintains it. no overcharging.
