Unstable engine idle at start up.
08-28-2007, 04:47 PM
#1
928 Engine Re-Re-Rebuild Specialist
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Unstable engine idle at start up.
Before I tear into my ISV or MAF to find the source of my unstable idle, I'm curious why the symptom is worst at cold start-up. It starts fine, but wants to stall when in idling gear. Putting it in neutral keeps it from stalling, but the idle still fluctuates.
Once the car is warm, the problem is almost non-existent. Idle holds (almost) steady.
I'm too lazy right now to use the "search" feature and sort through the results.
Once the car is warm, the problem is almost non-existent. Idle holds (almost) steady.
I'm too lazy right now to use the "search" feature and sort through the results.
08-28-2007, 06:08 PM
#4
928 Engine Re-Re-Rebuild Specialist
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I checked the ISV when I had the engine apart. Applying low voltage (6v from a latern battery) caused the valve to rotate its 90 degree path. It didn't seem to be sticking, but I guess shooting some WD-40 won't cause any permanent harm if it's not sticking.
08-29-2007, 06:15 AM
#7
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A badly aged MAF will make it impossible to set idle CO up to 1%.
Have you set idle CO and speed as per the workshop manual ?
Tenp 2 is much more important as regards cold start etc. Temp 1 is only used to alter igntion timing.
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08-29-2007, 10:41 AM
#8
928 Engine Re-Re-Rebuild Specialist
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It depends...... when the engine is cold, the O2 loop is ignor, as so fuelling is critically dependant on MAF calibration, but also depends on whether the idle CO has been set up as per the workshop manual. Also, ilde speed has to be set as per the workshop manual.
A badly aged MAF will make it impossible to set idle CO up to 1%.
Have you set idle CO and speed as per the workshop manual ?
Tenp 2 is much more important as regards cold start etc. Temp 1 is only used to alter igntion timing.
A badly aged MAF will make it impossible to set idle CO up to 1%.
Have you set idle CO and speed as per the workshop manual ?
Tenp 2 is much more important as regards cold start etc. Temp 1 is only used to alter igntion timing.
08-29-2007, 11:49 AM
#9
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It would be a good idea to go through that procedure, then you will know where you are....
To set the mixture is quite straightforward. Engine at normal operating temperature.
Disconnect the O2 sensor (this defaults the O2 loop to mid point) then adjust the pot on the MAF. (3mm hex) You may find there is a blanking plug over the CO pot. I drill a angled hole, and then force a self tapping scrw into the hole. Then use that to grip with pliers and lever out the bung.
You have to measure the CO before the cats of course....
Turn the pot clockwise to enrichen the mixture. Stop turning if the mixture stops getting richer. This is because the pot has no end stops, but can be damaged it turned repeatedly against its stops. If you think you have reached the end stop, disconnect the MAF and measure between pin 6 and the body of the MAF with an ohm meter. Maximum rich on the pot is 1000 ohms.
To set the mixture is quite straightforward. Engine at normal operating temperature.
Disconnect the O2 sensor (this defaults the O2 loop to mid point) then adjust the pot on the MAF. (3mm hex) You may find there is a blanking plug over the CO pot. I drill a angled hole, and then force a self tapping scrw into the hole. Then use that to grip with pliers and lever out the bung.
You have to measure the CO before the cats of course....
Turn the pot clockwise to enrichen the mixture. Stop turning if the mixture stops getting richer. This is because the pot has no end stops, but can be damaged it turned repeatedly against its stops. If you think you have reached the end stop, disconnect the MAF and measure between pin 6 and the body of the MAF with an ohm meter. Maximum rich on the pot is 1000 ohms.
08-29-2007, 11:53 AM
#10
928 Engine Re-Re-Rebuild Specialist
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Thread Starter
It would be a good idea to go through that procedure, then you will know where you are....
To set the mixture is quite straightforward. Engine at normal operating temperature.
Disconnect the O2 sensor (this defaults the O2 loop to mid point) then adjust the pot on the MAF. (3mm hex) You may find there is a blanking plug over the CO pot. I drill a angled hole, and then force a self tapping scrw into the hole. Then use that to grip with pliers and lever out the bung.
You have to measure the CO before the cats of course....
Turn the pot clockwise to enrichen the mixture. Stop turning if the mixture stops getting richer. This is because the pot has no end stops, but can be damaged it turned repeatedly against its stops. If you think you have reached the end stop, disconnect the MAF and measure between pin 6 and the body of the MAF with an ohm meter. Maximum rich on the pot is 1000 ohms.
To set the mixture is quite straightforward. Engine at normal operating temperature.
Disconnect the O2 sensor (this defaults the O2 loop to mid point) then adjust the pot on the MAF. (3mm hex) You may find there is a blanking plug over the CO pot. I drill a angled hole, and then force a self tapping scrw into the hole. Then use that to grip with pliers and lever out the bung.
You have to measure the CO before the cats of course....
Turn the pot clockwise to enrichen the mixture. Stop turning if the mixture stops getting richer. This is because the pot has no end stops, but can be damaged it turned repeatedly against its stops. If you think you have reached the end stop, disconnect the MAF and measure between pin 6 and the body of the MAF with an ohm meter. Maximum rich on the pot is 1000 ohms.
08-29-2007, 12:24 PM
#12
928 Engine Re-Re-Rebuild Specialist
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08-29-2007, 10:45 PM
#15
Man of many SIGs
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I have this same problem on my 84. Do I have an IFV or Temp I or II sensors?
Whats an IFV? I searched and this is the only thread that came up.
Whats an IFV? I searched and this is the only thread that came up.