Whine/rough idle
04-11-2012, 07:27 PM
#16
650RPM at idle is way off. The DME is set to idle these cars at 880RPMs, something is wrong. Would you say the car is idling much lower than before? Could be an intake air leak.
04-11-2012, 07:52 PM
#17
Burning Brakes
Thread Starter
I have only owned the car for 3 months and the idle was perhaps a bit higher, but not alot. When I PPi'd the car, the leakdown/compression numbers were near perfect. I think this weekend I'll dive in for some serious looking around.
04-11-2012, 08:00 PM
#18
I haddah Google dat
Rennlist Member
Rennlist Member
Leakdown and compression are totally different.
A more accurate description of the sound is needed.
What scarceller is saying is that a vacuum leak would cause a lean mixture because it admits false or unmetered air into the intake, which would result in a low idle. A vacuum leak is very likely.
A more accurate description of the sound is needed.
What scarceller is saying is that a vacuum leak would cause a lean mixture because it admits false or unmetered air into the intake, which would result in a low idle. A vacuum leak is very likely.
04-11-2012, 08:24 PM
#20
I haddah Google dat
Rennlist Member
Rennlist Member
Yes, please re-read Post #5, which mentions starting fluid. I would add, do a visual check of all hoses, manually check all hose clamps, and go over everything with a strong flashlight and an inspection mirror.
You can re-torque the intake manifolds with a swivel (universal joint), and a wobble extension on an allen head bit.
You can re-torque the intake manifolds with a swivel (universal joint), and a wobble extension on an allen head bit.
04-11-2012, 08:40 PM
#21
Burning Brakes
Thread Starter
Thanks guys.....everytime a part or area of the car is mentioned, I have to find out what and where it is....yes, thats where I am on the learning curve, but I am diligent with my learning. I did find this diagram to help me learn some of these things, but I think its a 964....anyone with something like this for an '86 911 ?
04-12-2012, 10:18 AM
#25
When you jumper pin B & C at the test connector it parks the ICV at 1/2 open 1/2 closed position. Once the ICV is parked it no longer can control idle, at this point you can use the air bypass screw on the TB to set the base idle near the target of 880RPMs. I suggest setting base idle at around 900RPMs, slightly above target. If this procedure can not get the base idle to 900 then something else is wrong.
Also note that setting the base idle usually should be proceeded by setting the CO level, you can also simply use a Wide Band O2 and set the idle AFR to 14.2 instead of setting CO.
One more common problem is a faulty O2 Sensor, I suggest a quick test where you just unplug the O2 sensor and see if you notice a change in RPM and exhaust sound. If all is well you should not notice anything when you unplug the O2. These sensors sometimes short out to ground, if this happens it tricks the DME to think the mixture is lean and the DME tries to correct by riching the mixture and this instantly results in a over-rich mixture.
Also note that setting the base idle usually should be proceeded by setting the CO level, you can also simply use a Wide Band O2 and set the idle AFR to 14.2 instead of setting CO.
One more common problem is a faulty O2 Sensor, I suggest a quick test where you just unplug the O2 sensor and see if you notice a change in RPM and exhaust sound. If all is well you should not notice anything when you unplug the O2. These sensors sometimes short out to ground, if this happens it tricks the DME to think the mixture is lean and the DME tries to correct by riching the mixture and this instantly results in a over-rich mixture.
04-12-2012, 12:39 PM
#26
Burning Brakes
Thread Starter
Yes, please re-read Post #5, which mentions starting fluid. I would add, do a visual check of all hoses, manually check all hose clamps, and go over everything with a strong flashlight and an inspection mirror.
You can re-torque the intake manifolds with a swivel (universal joint), and a wobble extension on an allen head bit.
You can re-torque the intake manifolds with a swivel (universal joint), and a wobble extension on an allen head bit.
I got some carb cleaner....thinking thats what Ed and yourself said to use, now I see he said starting fluid......can I use carb cleaner or should I get some starting fluid ?
04-12-2012, 01:01 PM
#27
04-12-2012, 02:02 PM
#30
Burning Brakes
Thread Starter
One more common problem is a faulty O2 Sensor, I suggest a quick test where you just unplug the O2 sensor and see if you notice a change in RPM and exhaust sound. If all is well you should not notice anything when you unplug the O2. These sensors sometimes short out to ground, if this happens it tricks the DME to think the mixture is lean and the DME tries to correct by riching the mixture and this instantly results in a over-rich mixture.