996 idle hunt with blower off only!
05-28-2015, 07:15 PM
#1
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996 idle hunt with blower off only!
Hi there,
I have a 1999 996. It runs really nicely but has one small fault:
When the blower is off, the idle will hunt between about 500-900rpm until left for about 10 seconds, then it will even out at about 750rpm. If you turn the blower on it will raise the idle to 900rpm and wont hunt at all. When reving the engine, the engine revs do not seem to drop as quickly as they should either.
Could someone please advise me as to what this could be? it is rather irritating.
Thanks in advance.
Luke.
I have a 1999 996. It runs really nicely but has one small fault:
When the blower is off, the idle will hunt between about 500-900rpm until left for about 10 seconds, then it will even out at about 750rpm. If you turn the blower on it will raise the idle to 900rpm and wont hunt at all. When reving the engine, the engine revs do not seem to drop as quickly as they should either.
Could someone please advise me as to what this could be? it is rather irritating.
Thanks in advance.
Luke.
05-28-2015, 07:23 PM
#2
Race Director
The blower? What do you mean? If you mean the air conditioner, it's true that running the AC causes idle to increase slightly and can help even out a hunting idle since the engine now has slightly greater load.
Does it hunt all the time (like at every stoplight), or when you first start the car? There are several factors that can cause the RPM to vary...a worn-out plug or coil pack, a fuel pump that isn't delivering consistent pressure, a dirty fuel filter, a dirty or bad MAF sensor, to name a few. Have you used an OBD-II scanner or Durametric to check for diagnostic codes?
One of the purposes served by your car's flywheel (assuming your car is a manual transmission) is to keep the RPMs up between shifts. If you want to defeat this, you can install a lightweight flywheel - but doing will make everyday driving less pleasant and may shorten the service life of other components, as a lightweight flywheel does not provide the harmonic damping produced by the factory dual-mass flywheel. An underdrive pulley will all the car to rev a bit more freely (although it won't affect how RPM drops off when you release the throttle)...
A video of the issue, along with as much additional detail you can provide, would greatly help.
Does it hunt all the time (like at every stoplight), or when you first start the car? There are several factors that can cause the RPM to vary...a worn-out plug or coil pack, a fuel pump that isn't delivering consistent pressure, a dirty fuel filter, a dirty or bad MAF sensor, to name a few. Have you used an OBD-II scanner or Durametric to check for diagnostic codes?
One of the purposes served by your car's flywheel (assuming your car is a manual transmission) is to keep the RPMs up between shifts. If you want to defeat this, you can install a lightweight flywheel - but doing will make everyday driving less pleasant and may shorten the service life of other components, as a lightweight flywheel does not provide the harmonic damping produced by the factory dual-mass flywheel. An underdrive pulley will all the car to rev a bit more freely (although it won't affect how RPM drops off when you release the throttle)...
A video of the issue, along with as much additional detail you can provide, would greatly help.
05-28-2015, 07:26 PM
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The blower? What do you mean?
If you mean the air conditioner, it's true that running the AC causes idle to increase slightly and can even out a hunting idle since the engine now has slightly greater load.
Does it hunt all the time (like at every stoplight), or when you first start the car?
Are you revving the engine with no load (neutral/clutch in)? If so, why?
If you mean the air conditioner, it's true that running the AC causes idle to increase slightly and can even out a hunting idle since the engine now has slightly greater load.
Does it hunt all the time (like at every stoplight), or when you first start the car?
Are you revving the engine with no load (neutral/clutch in)? If so, why?
It always hunts at idle, yes (unless AC on). And yes, when you blip the throttle with it in neutral, this is when you notice the revs not dropping as quickly as they ought to.
05-28-2015, 07:34 PM
#4
Race Director
Replacing the plugs and coil packs drastically reduced my car's hunting at idle. My car, also a '99, still had the original coil packs at 60K miles / 16 years, so it was overdue.
As far as the revs dropping off - don't know what to tell you. The engine is designed to run under load - it isn't optimized for revving in neutral. On the plus side, the car's tendency to keep the RPMs up will help keep your 996 in the power band and making decent horsepower as you work up through the gears...
As far as the revs dropping off - don't know what to tell you. The engine is designed to run under load - it isn't optimized for revving in neutral. On the plus side, the car's tendency to keep the RPMs up will help keep your 996 in the power band and making decent horsepower as you work up through the gears...
05-28-2015, 07:50 PM
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Replacing the plugs and coil packs drastically reduced my car's hunting at idle. My car, also a '99, still had the original coil packs at 60K miles / 16 years, so it was overdue.
As far as the revs dropping off - don't know what to tell you. The engine is designed to run under load - it isn't optimized for revving in neutral. On the plus side, the car's tendency to keep the RPMs up will help keep your 996 in the power band and making decent horsepower as you work up through the gears...
As far as the revs dropping off - don't know what to tell you. The engine is designed to run under load - it isn't optimized for revving in neutral. On the plus side, the car's tendency to keep the RPMs up will help keep your 996 in the power band and making decent horsepower as you work up through the gears...
Obviously an engine is designed to run under load but the revs not returning to tick over would seem to be a symptom linked to the hunting, which is why I mentioned it.
In relation to the power band comment, I don't know quite what you mean. a gear change doesn't take so long as to let the revs drop to below the rpm of the next gear, so my rev issue won't help or hinder the engine to stay in the power band.
Thank you for your response.
Luke.
05-28-2015, 08:09 PM
#6
Race Director
Could be a vacuum leak, could be a MAF issue, could be lots of things.
When you turn on the AC, the added load causes the RPM to increase slightly, which can cause the idle to smooth out. Same as very slightly depressing the accelerator - just a few hundred RPM difference can make the car hunt less...at least, that's how mine worked.
A video would help others understand if what you're describing with the RPM not falling off the way you want it to is abnormal behavior or if it's consistent with how other members' cars work.
When you turn on the AC, the added load causes the RPM to increase slightly, which can cause the idle to smooth out. Same as very slightly depressing the accelerator - just a few hundred RPM difference can make the car hunt less...at least, that's how mine worked.
A video would help others understand if what you're describing with the RPM not falling off the way you want it to is abnormal behavior or if it's consistent with how other members' cars work.
05-29-2015, 03:52 AM
#7
Burning Brakes
5CHN3LL is absolutely right. It can be a number of things. I would check for codes first and start with the MAF. German cars have a tendency of MAF malfunctioning. Try cleaning it with MAF cleaner and see if that will make a difference. That would be the cheapest and easiest route to start.
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05-29-2015, 05:47 AM
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5CHN3LL is absolutely right. It can be a number of things. I would check for codes first and start with the MAF. German cars have a tendency of MAF malfunctioning. Try cleaning it with MAF cleaner and see if that will make a difference. That would be the cheapest and easiest route to start.
I will research how to remove and clean the MAF and start with that.
05-29-2015, 05:48 AM
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Could be a vacuum leak, could be a MAF issue, could be lots of things.
When you turn on the AC, the added load causes the RPM to increase slightly, which can cause the idle to smooth out. Same as very slightly depressing the accelerator - just a few hundred RPM difference can make the car hunt less...at least, that's how mine worked.
A video would help others understand if what you're describing with the RPM not falling off the way you want it to is abnormal behavior or if it's consistent with how other members' cars work.
When you turn on the AC, the added load causes the RPM to increase slightly, which can cause the idle to smooth out. Same as very slightly depressing the accelerator - just a few hundred RPM difference can make the car hunt less...at least, that's how mine worked.
A video would help others understand if what you're describing with the RPM not falling off the way you want it to is abnormal behavior or if it's consistent with how other members' cars work.
05-29-2015, 05:55 AM
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5CHN3LL is absolutely right. It can be a number of things. I would check for codes first and start with the MAF. German cars have a tendency of MAF malfunctioning. Try cleaning it with MAF cleaner and see if that will make a difference. That would be the cheapest and easiest route to start.
05-29-2015, 10:43 AM
#11
Burning Brakes
05-29-2015, 12:31 PM
#12
Race Director
You can use any OBD-II code scanner. The Durametric allows you to access and change values for Porsche-specific stuff - but a cheapo OBD-II scanner (or a bluetooth/wifi OBD-II adapter and an app on your smartphone) will be sufficient.
You may throw a MAF-related diagnostic code running without the MAF - but it's harmless. The car will run with no MAF - and if it runs BETTER with no MAF, it's time for a cleaning or a new one.
You may throw a MAF-related diagnostic code running without the MAF - but it's harmless. The car will run with no MAF - and if it runs BETTER with no MAF, it's time for a cleaning or a new one.
05-29-2015, 05:55 PM
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So i took the throttle control valve off and cleaned it with some intake cleaner and i'd say its 75% better. I have an ultra sonic cleaner at our workshop so i will take it off and clean it in there to get the last bits of carbon off and hopefully then it will be spot on.
05-29-2015, 05:58 PM
#14
So i took the throttle control valve off and cleaned it with some intake cleaner and i'd say its 75% better. I have an ultra sonic cleaner at our workshop so i will take it off and clean it in there to get the last bits of carbon off and hopefully then it will be spot on.