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Car Stalls at low idle after Service
- GKEJ
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11 Jul 2025 15:12 - 11 Jul 2025 15:16 #22954
by GKEJ
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Car Stalls at low idle after Service was created by GKEJ
Hi, I had a service to drain and refill the coolant, change the oil and also the air filter.
When I started the car, it showed check coolant level. I assumed this was related to the coolant change. Drove the car for about 10 miles and at idle while waiting at traffic lights, the engine turned off. I did notice the Anti Lock light, mainly because this in my line of sight came on, however this could be because the engine stalled. Took the car back to the garage and they after waiting for the car to cool down a bit, added more coolant to the seam on the reservoir. It was showing halfway between the seam and bottom of reservoir when checking the levels before the mechanic had a look. The mechanic indicated that it was probably an air pocket. Whilst in the garage, at idle the engine stalled several times. At first the garage mechanic thought it was the fuel pump as it was audible. My thinking now is that when they changed the air filter, that maybe the MAF sensor was knocked or debris got in.
On the way home, when coming to a stop, on occasion, not every time the car would cut out, I also noticed the oil pressure guage fluctuating before it cut out and the Anti Lock light came on.
Before I go and get a replacement fuel pump, does anyone think that the issue maybe related to the change of air filter, which somehow affected the MAF sensor. The car before hand was running perfectly at idle and I had no warning lights, especially with the Anti Lock light.
I would say it was particularly warm in the UK, 30 degrees, but given that my car is an ex-Los Angeles car, I would have thought it should be able to handle a bit of heat. It might be worth mentioning that the car temp has always been near the three quarter mark when warmed up. See attached picture, my car just shows four markers, with the last red. Typically the needle will sit near the third mark.
Another odd thing was the Stop Light came on, but went off when I applied the brakes.
Any advice most welcome.
Porsche 928 S4 1989 LHD
Based in the UK
When I started the car, it showed check coolant level. I assumed this was related to the coolant change. Drove the car for about 10 miles and at idle while waiting at traffic lights, the engine turned off. I did notice the Anti Lock light, mainly because this in my line of sight came on, however this could be because the engine stalled. Took the car back to the garage and they after waiting for the car to cool down a bit, added more coolant to the seam on the reservoir. It was showing halfway between the seam and bottom of reservoir when checking the levels before the mechanic had a look. The mechanic indicated that it was probably an air pocket. Whilst in the garage, at idle the engine stalled several times. At first the garage mechanic thought it was the fuel pump as it was audible. My thinking now is that when they changed the air filter, that maybe the MAF sensor was knocked or debris got in.
On the way home, when coming to a stop, on occasion, not every time the car would cut out, I also noticed the oil pressure guage fluctuating before it cut out and the Anti Lock light came on.
Before I go and get a replacement fuel pump, does anyone think that the issue maybe related to the change of air filter, which somehow affected the MAF sensor. The car before hand was running perfectly at idle and I had no warning lights, especially with the Anti Lock light.
I would say it was particularly warm in the UK, 30 degrees, but given that my car is an ex-Los Angeles car, I would have thought it should be able to handle a bit of heat. It might be worth mentioning that the car temp has always been near the three quarter mark when warmed up. See attached picture, my car just shows four markers, with the last red. Typically the needle will sit near the third mark.
Another odd thing was the Stop Light came on, but went off when I applied the brakes.
Any advice most welcome.
Porsche 928 S4 1989 LHD
Based in the UK
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Last edit: 11 Jul 2025 15:16 by GKEJ. Reason: Correction to Grammar
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- Rich928
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16 Jul 2025 23:30 #22955
by Rich928
Rich
Membership Chairman
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1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
Replied by Rich928 on topic Car Stalls at low idle after Service
As long as the MAF has a screen in place, I don't believe there is much correlation between the air filter change and the MAF problems.
However, many owners do not know that the MAF is a service item, it drifts out of calibration (most often reporting lean) to a point where the lambda air/fuel regulation cannot compensate. The original MAF in my 1993 928 GTS had drifted out of calibration enough to require a rebuild/recalibration around 60,000 miles/100,000 km.
A noisy (significantly louder than normal) fuel pump is a good indication that it is failing. Insufficient fuel pressure could cause stalling.
The 1987 and newer 928s have automatic regulated idle speed. A small electronically activated valve opens and closes to maintain proper idle RPM. If your 928 doesn't hold proper idle, I'd first have a full tune-up done. Have the spark plug wires ever been replaced? If the idle speed still is too low, verify that the fuel pressure is within spec 3.6 (52 psi) to 4 bar (58 psi).
If the fuel pressure is proper, the idle speed regulation (ISR) valve may be sticking or carboned up. The intake manifold must be removed to access the ISR valve. It may clean up, or it may make sense to replace it. If the intake manifold is removed it would be a good idea to replace all the vacuum lines and fuel lines.
Regarding the engine temperature indication, please verify that both of the electric fans are operating. If one has failed that will cause this kind of issue. Check the coolant temperature with an IR heat gun to determine if the temperature gauge is accurate. My 928 S4 & GTS normally displays around 50% but on warm days or on steep hills requiring a lot of throttle the temp does display in the 3/4 range. A clogged radiator or failing thermostat can cause overheating.
However, many owners do not know that the MAF is a service item, it drifts out of calibration (most often reporting lean) to a point where the lambda air/fuel regulation cannot compensate. The original MAF in my 1993 928 GTS had drifted out of calibration enough to require a rebuild/recalibration around 60,000 miles/100,000 km.
A noisy (significantly louder than normal) fuel pump is a good indication that it is failing. Insufficient fuel pressure could cause stalling.
The 1987 and newer 928s have automatic regulated idle speed. A small electronically activated valve opens and closes to maintain proper idle RPM. If your 928 doesn't hold proper idle, I'd first have a full tune-up done. Have the spark plug wires ever been replaced? If the idle speed still is too low, verify that the fuel pressure is within spec 3.6 (52 psi) to 4 bar (58 psi).
If the fuel pressure is proper, the idle speed regulation (ISR) valve may be sticking or carboned up. The intake manifold must be removed to access the ISR valve. It may clean up, or it may make sense to replace it. If the intake manifold is removed it would be a good idea to replace all the vacuum lines and fuel lines.
Regarding the engine temperature indication, please verify that both of the electric fans are operating. If one has failed that will cause this kind of issue. Check the coolant temperature with an IR heat gun to determine if the temperature gauge is accurate. My 928 S4 & GTS normally displays around 50% but on warm days or on steep hills requiring a lot of throttle the temp does display in the 3/4 range. A clogged radiator or failing thermostat can cause overheating.
Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
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