Hesitation when cold and poor idle – Possible Cause/Fix??????
01-30-2002, 01:24 PM
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Hesitation when cold and poor idle – Possible Cause/Fix??????
I have a ’90 C2 Coupe, 5 speed. It has 42,000 miles, and I am the third owner. The car recently (200 miles ago) had a major service (valve adjustment, plugs, caps, rotors, belts, filters). The distributor belts have been replaced and a vent kit installed. The car is completely stock. I have owned it for 2 months.
Since I took delivery, there has been a slight hesitation when cold. Idle was fine, but there was a pronounced hesitation between 3,000 and 4,000 RPM. After the first mile or so of driving at moderate speed, and with the oil temp gauge beginning to move up, the problem cleared. It was hoped that the tune-up would take care of that, but other, more obvious problems have begun to occur (possibly related, or perhaps not). The minor hesitation was not noticed by the shop at the time of the major service.
Another issue, although a very intermittent one, was that on 3 occasions, I experienced a complete cut in power. Twice pulling away for a stop sign, and once at about 45 MPH in third gear. The car did not stall (I quickly put the clutch in, and was able to modulate the throttle), but it was a pretty severe loss of power. When I mentioned this to the shop, his first thought was that there were an issue with the DME relay. This was replaced with a new relay, but as you will read, did not solve the problem.
As of a couple days ago, when starting in the morning, the idle is unstable, and the engine will want to stall. I can keep it running by modulating the throttle, but the revs oscillate between 1300 RPM and stalling. Over the first mile or so of driving, the car bucks severely, as if the throttle were cutting out completely. I can keep it from stalling but putting the clutch in and modulating the throttle. Again, after the first mile or so, the car seems fine. I would also mention that the car is stored in an unheated, but attached garage. The overnight outside temperature has been in the mid thirties to low forties lately.
The car is heading to the shop this afternoon (an independent shop that is regarded as the best shop for Porsche in my city). In speaking with my mechanic and describing the problem, his first guess is a problem with the head temperature sensor or possibly the oxygen sensor. He also mentioned the idle control vale.
I have my fingers crossed, and can only hope the problem will rear its ugly head when in the presence of the mechanic.
My purpose here is to see if others have seen the same problem, and to get a handle on what the possible solutions may be. I want to have a list of possible solutions based on the experience of others.
As a side note, my shop does not have the ability to read the codes in the DME. My question regarding the DME is this: would the DME tell me anything in terms of an intermittent sensor, or would it only be useful to detect only total failure?
Thanks in advance for any input you may have.
Brian Leduc
Since I took delivery, there has been a slight hesitation when cold. Idle was fine, but there was a pronounced hesitation between 3,000 and 4,000 RPM. After the first mile or so of driving at moderate speed, and with the oil temp gauge beginning to move up, the problem cleared. It was hoped that the tune-up would take care of that, but other, more obvious problems have begun to occur (possibly related, or perhaps not). The minor hesitation was not noticed by the shop at the time of the major service.
Another issue, although a very intermittent one, was that on 3 occasions, I experienced a complete cut in power. Twice pulling away for a stop sign, and once at about 45 MPH in third gear. The car did not stall (I quickly put the clutch in, and was able to modulate the throttle), but it was a pretty severe loss of power. When I mentioned this to the shop, his first thought was that there were an issue with the DME relay. This was replaced with a new relay, but as you will read, did not solve the problem.
As of a couple days ago, when starting in the morning, the idle is unstable, and the engine will want to stall. I can keep it running by modulating the throttle, but the revs oscillate between 1300 RPM and stalling. Over the first mile or so of driving, the car bucks severely, as if the throttle were cutting out completely. I can keep it from stalling but putting the clutch in and modulating the throttle. Again, after the first mile or so, the car seems fine. I would also mention that the car is stored in an unheated, but attached garage. The overnight outside temperature has been in the mid thirties to low forties lately.
The car is heading to the shop this afternoon (an independent shop that is regarded as the best shop for Porsche in my city). In speaking with my mechanic and describing the problem, his first guess is a problem with the head temperature sensor or possibly the oxygen sensor. He also mentioned the idle control vale.
I have my fingers crossed, and can only hope the problem will rear its ugly head when in the presence of the mechanic.
My purpose here is to see if others have seen the same problem, and to get a handle on what the possible solutions may be. I want to have a list of possible solutions based on the experience of others.
As a side note, my shop does not have the ability to read the codes in the DME. My question regarding the DME is this: would the DME tell me anything in terms of an intermittent sensor, or would it only be useful to detect only total failure?
Thanks in advance for any input you may have.
Brian Leduc
01-30-2002, 01:29 PM
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Brian
These problems are much easier to rectify if the garage has a Bosch Hammer.
Otherwise it is long process of swapping parts and trial and error
Do you not have a garage close by with Bosche diagnostic equipment or an official porsche dealership?
Otherwise you are paying a high labour cost for their lack of eqipment
These problems are much easier to rectify if the garage has a Bosch Hammer.
Otherwise it is long process of swapping parts and trial and error
Do you not have a garage close by with Bosche diagnostic equipment or an official porsche dealership?
Otherwise you are paying a high labour cost for their lack of eqipment
01-30-2002, 02:51 PM
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Hi,
I agree - definitely try to find somewhere that can at least check fault codes with a hammer, because this may save you lots of time / money in the long run. You can still use your current mechanic for the actual fix.
One other point - if the cold start problem is there the instant that the car fires up, then it's probably not the O2 sensor. I remember from when I had idle hunting problems and looked back through the archives, I saw a number of posts saying that the O2 sensor is not used from stone cold - it cuts in about 90s after totally cold start I believe. Of course, your problems may have more than one cause so the O2 sensor could still be faulty.
Dave
90 C4
I agree - definitely try to find somewhere that can at least check fault codes with a hammer, because this may save you lots of time / money in the long run. You can still use your current mechanic for the actual fix.
One other point - if the cold start problem is there the instant that the car fires up, then it's probably not the O2 sensor. I remember from when I had idle hunting problems and looked back through the archives, I saw a number of posts saying that the O2 sensor is not used from stone cold - it cuts in about 90s after totally cold start I believe. Of course, your problems may have more than one cause so the O2 sensor could still be faulty.
Dave
90 C4
02-03-2002, 06:27 AM
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Brian,
you may want to check out an earlier thread titled "total muscle failure". I too experienced a similar problem with my C2 - total loss of power, without stalling. It was an intermittent problem (i.e. tended to disappear when the mechanic was near) and was difficult to diagnose, but was eventually traced to the idle control valve. Had it replaced and the problem has not resurfaced for a few months now.
Some other problems (not sure if they are related) have happened in the interim (ocassional stalling, poor hot starting) which was also intermittent was eventually to a faulty air flow meter...had it replaced and it's fine now.
Good luck with your car, I know how annoying these faults can be.
Raymond
you may want to check out an earlier thread titled "total muscle failure". I too experienced a similar problem with my C2 - total loss of power, without stalling. It was an intermittent problem (i.e. tended to disappear when the mechanic was near) and was difficult to diagnose, but was eventually traced to the idle control valve. Had it replaced and the problem has not resurfaced for a few months now.
Some other problems (not sure if they are related) have happened in the interim (ocassional stalling, poor hot starting) which was also intermittent was eventually to a faulty air flow meter...had it replaced and it's fine now.
Good luck with your car, I know how annoying these faults can be.
Raymond
02-03-2002, 11:14 AM
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Annoying and frustrating does not begin to describe it......
The car has been with the mechanic since Wednesday. If I understood corerctly, he beleives that the problem is related to the "reference sensor", although given the transient nature of the problem, it is not 100%.
I did note the posts about "total muscle failure" and mentioned the idle control valve (he had also mentioned it as a possible cause). I believe that he checked this over and found no problem. It was his opionion that the O2 sensor would not cause this symptom, but he did check it, and feels it is OK.
FTR, I have seen mention of the Ref Sensor elswhere (the Bodymotion site), and it does seem to produce similar symptoms. He laso has swapped the head temp sensor, since he felt it was easy enough to do while changing the reference sensor.
Unfortunately, while checking into that problem, he noted a problem with the #1 cyclinder not firing properly. The cap, plug, rotor, and plug wire, are all OK, so he is looking at other problems (injector??).
To be truthful, at the moment I do not fully grasp the scope of this new problem, but will discuss on Monday morning.
I appreciate the tips so far, and will post the results once this minor nightmare is resolved.
This is my first Porsche, the culmination of a lifelong desire to own one, and when it is running, its is fabulous, but I sure wish that it had some of the reliability (and freedome for oil leaks!) that my Mazda's, Honda's, and Acura had!
BL
The car has been with the mechanic since Wednesday. If I understood corerctly, he beleives that the problem is related to the "reference sensor", although given the transient nature of the problem, it is not 100%.
I did note the posts about "total muscle failure" and mentioned the idle control valve (he had also mentioned it as a possible cause). I believe that he checked this over and found no problem. It was his opionion that the O2 sensor would not cause this symptom, but he did check it, and feels it is OK.
FTR, I have seen mention of the Ref Sensor elswhere (the Bodymotion site), and it does seem to produce similar symptoms. He laso has swapped the head temp sensor, since he felt it was easy enough to do while changing the reference sensor.
Unfortunately, while checking into that problem, he noted a problem with the #1 cyclinder not firing properly. The cap, plug, rotor, and plug wire, are all OK, so he is looking at other problems (injector??).
To be truthful, at the moment I do not fully grasp the scope of this new problem, but will discuss on Monday morning.
I appreciate the tips so far, and will post the results once this minor nightmare is resolved.
This is my first Porsche, the culmination of a lifelong desire to own one, and when it is running, its is fabulous, but I sure wish that it had some of the reliability (and freedome for oil leaks!) that my Mazda's, Honda's, and Acura had!
BL
02-03-2002, 02:43 PM
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Brian;
A friend of mine had a stalling/engine cut out problem with a 964 that he use to own two years ago. The car would die and stall, he replaced the coils, checked fuel pumps, checked and swapped DME's with me. It was finally traced down to a faulty crank position sensor, located on the back of the engine. On inspection, it looked as if a previous mechanic had brushed it with the flywheel on an earlier clutch job. It cured his problem. His symtoms were a complete engine cutout. It would take a while for him to restart. It looked like a fuel starvation problem, or vapor lock.
A friend of mine had a stalling/engine cut out problem with a 964 that he use to own two years ago. The car would die and stall, he replaced the coils, checked fuel pumps, checked and swapped DME's with me. It was finally traced down to a faulty crank position sensor, located on the back of the engine. On inspection, it looked as if a previous mechanic had brushed it with the flywheel on an earlier clutch job. It cured his problem. His symtoms were a complete engine cutout. It would take a while for him to restart. It looked like a fuel starvation problem, or vapor lock.
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02-05-2002, 02:32 PM
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It appears that the problem has been solved.
My mechanic found a TSB on ALLDATA refering to a reccomended update to the wiring harness for the Air Flow Sensor. For those that have ALLDATA access, the reference number is 29005, dated 4/6/90.
The procedure calls for the harness to be openned up at the plug, and certain wires seperated from certain other wires.
As luck would have it, my car was built several days before the factory began to produce the harness with a fix that eliminates the problem. They do reccomend that all cars built before this have the update performed, even if you do not have evidence of the problem.
Thanks to all those that offered assistance.
BL
My mechanic found a TSB on ALLDATA refering to a reccomended update to the wiring harness for the Air Flow Sensor. For those that have ALLDATA access, the reference number is 29005, dated 4/6/90.
The procedure calls for the harness to be openned up at the plug, and certain wires seperated from certain other wires.
As luck would have it, my car was built several days before the factory began to produce the harness with a fix that eliminates the problem. They do reccomend that all cars built before this have the update performed, even if you do not have evidence of the problem.
Thanks to all those that offered assistance.
BL
02-05-2002, 05:16 PM
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Just a point of clarification.
I actually read the TSB this afternoon, and what is actually happenning is that the harness plug cover is modified such that the harness does not contact the engine vent hoses.
The procedure modifies the harness so the wires can be routed to NOT touch the vent hoses.
All that said, I don't know that I can explain in electrical terms what was happenning, but it sure as heck sorted out the problem.
BL
I actually read the TSB this afternoon, and what is actually happenning is that the harness plug cover is modified such that the harness does not contact the engine vent hoses.
The procedure modifies the harness so the wires can be routed to NOT touch the vent hoses.
All that said, I don't know that I can explain in electrical terms what was happenning, but it sure as heck sorted out the problem.
BL
