97-993C4 rough idle
#1
97-993C4 rough idle
Ok gang, a little help please.
I'm the 2nd owner of the car which is coming up on 100k miles. I've had the car for almost 4 years and it's always had a rough idle. Even to the point that on occasion it stalls as I slow down for a stop light.
However... If I've got the a/c on the car idles fine and never stalls. Any ideas on why? Everyone just recommends getting the top end done. I'd love to not spend the $6.5k to do that if I don't have too!! All ideas will be greatly appreciated!
Dan
I'm the 2nd owner of the car which is coming up on 100k miles. I've had the car for almost 4 years and it's always had a rough idle. Even to the point that on occasion it stalls as I slow down for a stop light.
However... If I've got the a/c on the car idles fine and never stalls. Any ideas on why? Everyone just recommends getting the top end done. I'd love to not spend the $6.5k to do that if I don't have too!! All ideas will be greatly appreciated!
Dan
#2
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Probably a tiny vacuum leak somewhere ... my car idles just a little bit low without the AC on, and I've never been able to chase it. It doesn't come close to stalling (and I have the RS clutch and lightweight flywheel which makes the car easier to stall and it never has) but it shakes a tiny bit -- unless the AC is on, then it idles like a champ. (When the ECU senses that the AC is on, it bumps the idle a little to compensate, and that's just enough to smooth it out.) You might clean and try adjusting the idle stabilization valve to see if that helps (ISV).
I've also been told that this is just an inherent a characteristic of some 993s (and this is not the first 993 I've owned that has done the same thing), and it can be fixed with a custom ECU that just bumps it up 100 rpms or so (TechArt, Rennsport, etc.), but I can tell you definitively that my car shook a little at idle before I did the top end, and it did it after the top end, too, so I don't think that will cure you.
I've also been told that this is just an inherent a characteristic of some 993s (and this is not the first 993 I've owned that has done the same thing), and it can be fixed with a custom ECU that just bumps it up 100 rpms or so (TechArt, Rennsport, etc.), but I can tell you definitively that my car shook a little at idle before I did the top end, and it did it after the top end, too, so I don't think that will cure you.
#3
Drifting
First thing you should do, as vjd3 suggests:
http://www.pcarworkshop.com/index.ph...-_ISV_Cleaning
Last thing you should do, is rebuild the motor to fix an idle problem.
http://www.pcarworkshop.com/index.ph...-_ISV_Cleaning
Last thing you should do, is rebuild the motor to fix an idle problem.
#4
Nordschleife Master
If your service is all up to date, it's either a vacuum leak (vacuum lines pop off easily) a dirty/bad ISV ( idle valve), or a failing flywheel sensor. The MAF might also need a cleaning, but it should throw a code, it may not hurt to see if there are any stored codes that are not throwing a CEL.
#5
There are a few threads that attribute a failing dual-mass flywheel to rough idle. I don't quite understand what happens to the DMF to cause this- maybe someone can chime in with an explanation.
#6
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You can also adjust the ISV to get a slightly higher idle...I did this due to my RS pulley setup in order to help the alternator at idle..
Cheers,
Mike
Cheers,
Mike
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#8
Rennlist Member
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.
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.
#9