Will bad guides throw misfires and rough idle?
08-02-2005, 04:33 PM
#31
Originally Posted by Laura
Mike,
Do you have the original dual mass flywheel?
With the miles you stated, if you do it could be signs that it is failing. The clutch operation could be working fine and as such gives no indication. But the crank sensor obtains readings from the fywheel and if those are interrupted because of wear it senses misfire, sends codes to the computer, CEL light illuminates, fault code reads misfire.
Have your mechanic read the computer and note at what RPM the misfires occur.
Do you have the original dual mass flywheel?
With the miles you stated, if you do it could be signs that it is failing. The clutch operation could be working fine and as such gives no indication. But the crank sensor obtains readings from the fywheel and if those are interrupted because of wear it senses misfire, sends codes to the computer, CEL light illuminates, fault code reads misfire.
Have your mechanic read the computer and note at what RPM the misfires occur.
Laura,
I have 92k on my 96 993. The DMF and clutch were replaced at 86k due to the CEL and misfires with a rough idle. The codes were cleared and off (although the car still ran rough at idle) until yesterday. I was driving around the city and got in and out of the car a few times, starting and stopping the engine. It came on out of the blue when I started it. Today I checked it with an obdII scanner and up came P0300, mulriple random misfires. I called the dealer who replaced the DMF and clutch (6k miles ago) to see if it'd be under their warranty or Porsche's for that matter. I booked an appointment for next week and hopefully it's covered.
Any other ideas on what it could be? Just before the DMF and clutch were replaced, they did the plugs, caps, rotors, wires, and belts. If i had to guess I couldn't. I just hope they take care of it. I looked at the back of the reciept and it states a warranty of 24 months and unlimited mileage on the repair.
08-08-2005, 01:59 AM
#32
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Hi Allill,
I think that a failed DMF will not give a rough idle but fool the crank sensor into thinking there is a misfire. A failed DMF could be "sloppy" running at an inconsistent speed ; hence the sensor gets inconsistent signals and thinks its a misfire. In my case the car actually shakes and there is a misfire noise at idle in both exhausts. The PO also replaced my DMF about 30,000 miles ago. Because of the backfire noise and the crappy leakdown test I have concluded its guides.
Can you feel the rough idle? Does it go away when the clutch is depressed?
At 92K you certainly are getting ready for guides. What is your oil consumption?
Cheers,
Mike
I think that a failed DMF will not give a rough idle but fool the crank sensor into thinking there is a misfire. A failed DMF could be "sloppy" running at an inconsistent speed ; hence the sensor gets inconsistent signals and thinks its a misfire. In my case the car actually shakes and there is a misfire noise at idle in both exhausts. The PO also replaced my DMF about 30,000 miles ago. Because of the backfire noise and the crappy leakdown test I have concluded its guides.
Can you feel the rough idle? Does it go away when the clutch is depressed?
At 92K you certainly are getting ready for guides. What is your oil consumption?
Cheers,
Mike
08-08-2005, 02:19 AM
#34
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Originally Posted by gst
check if its the defective MAF, or air flow meter , whatever its called
Cheers,
Mike
10-28-2007, 12:05 AM
#35
Burning Brakes
I've subscribed to this thread. I'm having the exact same problem in terms of rough idle and random misfires. Even had a blinking CEL for a moment today. Car runs hard at the track (was at Sears Point today, going back tomorrow), but on the grid she idles pretty rough. The choices outlined: valve guides, DMF - ouch.
10-28-2007, 01:54 AM
#36
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I've subscribed to this thread. I'm having the exact same problem in terms of rough idle and random misfires. Even had a blinking CEL for a moment today. Car runs hard at the track (was at Sears Point today, going back tomorrow), but on the grid she idles pretty rough. The choices outlined: valve guides, DMF - ouch.
As you might know it did turn out to be the guides. I did the DIY rebuild and the car is running strong now (in fact people comment how strong the car really is...I advanced the cams a bit more than stock and that seemed to help the top end quite a bit). Anyways the guides were worn quite a bit and close to the limit...but not excessively. But after I rebuilt the engine and put it back together the **phut** **phut** went away and the engine is good.
What is your oil consumption and do you get a **phut** **phut** sound?
Cheers,
Mike
10-28-2007, 02:15 AM
#37
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Mike:
FWIW,..advancing cam timing boosts low-end power to the detriment of upper RPM
output.
Retarding the cam timing gives a small higher RPM boost, with a reduction in low-end torque.
This works the same way in all engines unless the camshaft profile is wildly off to begin with. In those instances, there are usually other issues.
FWIW,..advancing cam timing boosts low-end power to the detriment of upper RPM
output.
Retarding the cam timing gives a small higher RPM boost, with a reduction in low-end torque.
This works the same way in all engines unless the camshaft profile is wildly off to begin with. In those instances, there are usually other issues.
10-28-2007, 02:18 AM
#38
Burning Brakes
Hey Don,
As you might know it did turn out to be the guides. I did the DIY rebuild and the car is running strong now (in fact people comment how strong the car really is...I advanced the cams a bit more than stock and that seemed to help the top end quite a bit). Anyways the guides were worn quite a bit and close to the limit...but not excessively. But after I rebuilt the engine and put it back together the **phut** **phut** went away and the engine is good.
What is your oil consumption and do you get a **phut** **phut** sound?
Cheers,
Mike
As you might know it did turn out to be the guides. I did the DIY rebuild and the car is running strong now (in fact people comment how strong the car really is...I advanced the cams a bit more than stock and that seemed to help the top end quite a bit). Anyways the guides were worn quite a bit and close to the limit...but not excessively. But after I rebuilt the engine and put it back together the **phut** **phut** went away and the engine is good.
What is your oil consumption and do you get a **phut** **phut** sound?
Cheers,
Mike
I don't think I get a phut phut sound - I'll check again tomorrow. Just a stumbling idle and many CELS. Don't really think I have much oil consumption - it's a little hard to tell in the sense the car is driven only very, very hard.
10-28-2007, 02:31 AM
#39
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Mike:
FWIW,..advancing cam timing boosts low-end power to the detriment of upper RPM
output.
Retarding the cam timing gives a small higher RPM boost, with a reduction in low-end torque.
This works the same way in all engines unless the camshaft profile is wildly off to begin with. In those instances, there are usually other issues.
FWIW,..advancing cam timing boosts low-end power to the detriment of upper RPM
output.
Retarding the cam timing gives a small higher RPM boost, with a reduction in low-end torque.
This works the same way in all engines unless the camshaft profile is wildly off to begin with. In those instances, there are usually other issues.
In the rebuild I swapped in the 964- gearset and my cams had the woodruf keys so I could time the cams the old fashioned way using a gauge. I used solid lifters with the standard valve lash and did it that way since I do not own the expensive factory tools to do this...and I would rather do it with a guage anyways.
Cheers,
Mike
