Idling/stalling issue - '89 635csi

[psd360]

Hi,

I've got a 1989 635csi (UK), when the car starts cold the idle is smooth, however after 20-25 mins (when the car is up to temperature), it will start to jump/fluctuate in revs, the only way to keep the car from stalling is by stopping the car from idling, which means applying acceleration and even when accelerating it can be hesitant to accelerate/fluctuating revs.

As mentioned before, this only happens when the car is fully warmed up. In the first 20 mins of driving the car from cold, it drives perfectly.

Idle control valve has been replaced
AFM has been replaced
Throttle body/Throttle position sensor checked
2 vacuum leaks next to the AFM were detected, those pipes were replaced and no other air leaks were detected
The ECU was tested and came out with no issues, we also tried swapping the ECU with a test ECU

The above has been done, and the result has been not much difference, it will still constantly die at idle after warm up.

There were also a bunch of parts changed before I took on the project: HT ignition leads, crank sensor, temp sensor, coolant level sensor, ignition coil, distributor cap+rotor arm, spark plugs, air filter, fuel filter (underwent a full service).

Any ideas what the issue could be here?

[Ralph in Socal]

Check coolant temp sensor and it’s wiring. My experience with the B35 is limited but on the earlier cars it’s very easy to misconnect the connectors and sensors

Ralph

[Ronnie Wilson]

Hi , Have you checked your Injectors for good spray pattern. Check the Fuel Delivery rate, as per Bentley Manual and the Fuel Pressure regulator.
Checking both of these will require a Fuel Pressure Gage kit.

Good look.

[miklilmag]

Check coolant temp sensor and it’s wiring. My experience with the B35 is limited but on the earlier cars it’s very easy to misconnect the connectors and sensors

Ralph

THIS!
Replace the coolant sensor and check the wiring, special attention to where the wire meets the plugins!

Good luck!
Franke

[psd360]

Hi, thanks for everyone’s replies.

I tested the harness connector that goes into the temperature sensor for the ECU (with the blue top), when the ignition was on the multimeter was showing 5 volts, so the wiring to the sensor seems to be fine.

I then tested the resistance on the temp sensor for the ECU, when I started the engine cold it was around 1800 ohms, 5-10 mins later it went down to around 700/750.

Are these values correct ? Could the coolant temp sensor need replacing ? This is a new sensor that was replaced a few months ago from the previous owner, but was not bought from BMW. This is the sensor which was bought:

https://www.eurocarparts.com/p/bosch-te ... -224110077



Thanks

[baders]

This is the applicable paragraph from the Bosch Motronic Guide by Hi Performance Store;

If you have a 528e with Motronic 1.1 or a 535i you are looking for a slightly different set of values. With a coolant temperature of 12-16F (-9C to -11C) resistance between the two terminals should be 8200-10500 ohms. At a coolant temperature of 66F-70F (19C-21C) it should be 2200-2700 ohms. When the engine is fully warmed up the coolant temperature should be 174F-178F (79C-81C) and you should have 300-360 ohms of resistance.

It's not far off but MAY be wayward enough to be a problem. Here's a cheaper option from FCPEuro, though delivery may make a difference;
https://www.fcpeuro.com/products/bmw-vo ... escription

The above is a Bosch Volvo/BMW part and is the superseded BMW 13621709966 @ US$15.10. Part number BMW 13621709967 is the genuine BMW replacement for 966 @ US$62.11 . RealOEM page describing both;
https://www.realoem.com/bmw/enUS/showpa ... Id=11_0708

Why not just replace the CTS at these prices ?

[psd360]

Fitted a new CTS, no improvement I'm afraid, car began to stall whilst in Park after around 25 minutes of warming up.