Euro 520i lousy when warm weather

[fahrenheit]

Hello,

I have following problem:
Car feels really lousy and idle is rough at warm summer days. Now it's colder (0 Celcius, 32 Fahrenheit) and it get revs much much guicker and feels more powerful. What could cause the problem?

Thanks!

[tn535i]

I assume this car has a coolant temp sensor (CTS). I would start there.

[fahrenheit]

I assume this car has a coolant temp sensor (CTS). I would start there.

There is two sensors on thermostat housing but can't really tell what those are measuring.

[Mike W.]

Brown is thermo time switch for the cold start valve, white or sometimes blue is the FI coolant temp sensor.

[fahrenheit]

Brown is thermo time switch for the cold start valve, white or sometimes blue is the FI coolant temp sensor.

Thank you very much. Can I just remove that temp sensor without coolant loss?

[Mike W.]

Brown is thermo time switch for the cold start valve, white or sometimes blue is the FI coolant temp sensor.

Thank you very much. Can I just remove that temp sensor without coolant loss?

Maybe without too much coolant loss if it's cold, but make sure you have the cap off just in case so you don't get a facefull of scalding water. It is in direct contact with coolant so you will have some loss, but not too much if you are reasonably quick.

[tn535i]

While the car is cool or has cooled significantly remove the expansion tank cap to relieve any pressure. Reinstall the cap so that when you pull the sensor it will make a slight vacuum and hardly anything will come out if you are quick. You will also not need to re-bleed.

If you have access to a meter you can check the resistance hot and cold. Something like 2500+ ohms cold and 3-400 hot is about right. If not replace it. If you want to test the theory and have access to resistors stick a 400 ohm resistor across the harness leads once it warms up and see if it runs better.

There are two part numbers, the old one is white usually and the new one is blue. Get the newer blue one and try to get a Bosch. The newer one uses a separate seal washer and has a tighter tolerance, otherwise either will work fine.

[JohnH]

Brown is thermo time switch for the cold start valve, white or sometimes blue is the FI coolant temp sensor.

Thank you very much. Can I just remove that temp sensor without coolant loss?

From the picture it appears that you are running LE2-Jetronic.
Brown is the single wire coolant temperature connector for the temperature gauge.
Off white is the twin wire coolant temperature connector for the fuel injection computer.

Before you take it all apart check the sensor resistance measurement at the injection computer connector. Detach it from the ecu first.
This sensor part #13621709966 is used in all post 9/84 e28/30/e34. the specs for it can be found in the various manuals for these or check here https://www.bmwtechinfo.com/repair/main/247en/index.htm You are interested in Group 13 Fuel system, 62 Coolant temperature sensor. find the column with the last few digits of the part number and use the values listed there.

[fahrenheit]

First of all I want to thank all of you for being so helpful!

So I check those ohms from ecu connector? Not from sensor itself?

[JohnH]

Initially check them at the disconnected ecu connector pin 10 brown/red (for the multimeter positive) and pin 13 brown for your multimeter negative. Meter set to Ohms. Do it with the engine stone cold and then take it for a run to completely warm it up and do it again. If the hot ohms are out of range test at the sensor. If the same result, then the sensor is kaput and needs replacing. If the reading at the sensor is in range, then you have a wiring fault between the sensor and ecu.

To answer your original question. Yes you can unscrew the sensor without losing to much coolant if you are quick. It can be a bit fiddly.

Heres the LE2-Jetronic wiring diagram. 8 is the coolant sensor and 1 to ecu.

[fahrenheit]

Initially check them at the disconnected ecu connector pin 10 brown/red (for the multimeter positive) and pin 13 brown for your multimeter negative. Meter set to Ohms. Do it with the engine stone cold and then take it for a run to completely warm it up and do it again. If the hot ohms are out of range test at the sensor. If the same result, then the sensor is kaput and needs replacing. If the reading at the sensor is in range, then you have a wiring fault between the sensor and ecu.

Wow, I appreciate your help so much. Thanks!
Now it's all clear. Tomorrow I'll check those ohms and replace the coolant sensor if needed. I'll tell you the results.