Vibrating Idle in neutral – E30 318I Auto

[Sameer Adams]

Hi guys,

I have a 1991 E30 318i Automatic.

The problem:
The whole car vibrates when idling in neutral when in normal operating temperature.
Power delivery is smooth when driving with no flat spots, so its just the idling that rattles the car.

• The brake system was reconned by previous owner but but takes quite low down to stop the car
• I've cleaned out and dried the oxygen sensor with spark cleaner
• Cleaned out and dried the throttle butterfly and the pipe between filter box and intake with carb cleaner
• Cleaned out and dried the idle control valve
• There is an issue with the radiator leaking transmission fluid (that feeds the gearbox) but thats being replaced now.
• I replaced the spark plugs with BMW specced ones
• The vac hoses all seem fine

My mechanic told me that the automatic e30 318i's never have a completely smooth idle but I'm reluctant believe this.
Can anyone please shed some light on how to further solve this issue?

Much thanks in advance!

 

[samman325]

Hi Sameer,

What is the condition of the engine and transmission mounts?

 

[JayDrft]

Im leaning towards a loose torque converter.

Thats the only bit in the car that has enough momentum to vibrate the whole car...As far as I can understand.

 

[M302]

Does the vibration only happen at operating temperature ?

 

[bobbychoo]

as some have said already it can be drive shaft related, check your prop-shaft coupling, engine mounts.

 

[Don1]

Check if the cooling fan is ok. It could have a broken fan blade

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[Jeremy.d]

I commented on e30ClubSA also, but could it be the airflow meter?
Is the vibration because the revs are low, or is it idling at the right RPM?

 

[Sameer Adams]

Thank you for all your responses! :ty:

@ samman325
Engine and transmission mounts are in very good nick

@ JayDrft
If the torque converter is lose can it be tightened DIY style?

@ M302 and Jeremy.d
Yes only starts when in normal operating temp cos then the revs drop to between 7000 - 8000 rpms

@ bobbychoo
The car only rattles when not in motion, meaning that the drive shaft is not spinning it rattles

---

Check if the cooling fan is ok. It could have a broken fan blade

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That component is in good nick too.

 

[Don1]

Also check if the heat shield is clear of the exhaust and all exhaust hangers are ok. Vibrations can transfer from the exhaust system to the body of the car

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[zippy320]

I had a similar issue with my 320i Auto a long long time ago, I did the same to my ICV many times , It seemed to have cleaned it , the ICV worked when i tested it ,but it never solved the problem , I eventually replaced it with a new part from BMW and that fixed the problem . Makes me wonder if the motor inside gets weak over time .

Much Much Later on the problem resurfaced so I replaced the coolant temp sensor , the one that gives the ECU a signal I think its the brown one. The Bosch ones are cheap and its an easy swap . If its giving the wrong signal that could cause a rough idle as well as high fuel consumption. If its only happening at normal operating temp then I suspect its that temp sensor . If I remember correctly When cold , I know my car is supposed to work at a default value , then as it heats up the temp sensor gives the ECU a reading to optimize fuel / air delivery or something like that . This also fixed my problem .