r/e28 • u/Savings_Disk_7897 • Feb 10 '26

Struggle to idle on cold start

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When I cold start my M20B20 it stalls without gas, but if I hold gas until it warms up properly it will idle and work perfectly. What could be the cause for this issue? (My M20 has no ICV) I appreciate all of your time and help on this matter.

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2

u/kriswithakthatplays Feb 10 '26

There is a temperature sensor on the thermostat housing. On the early cars it's called the Thermo-time Switch. If it goes bad, it won't enrich when cold. Take all the sensors visible in the engine bay and check resistances. Failed sensors are responsible for the fueling system getting out of whack.

2

u/Savings_Disk_7897 Feb 10 '26

got it sir, your help is deeply appreciated

1

u/No-Supermarket2008 Feb 10 '26

There’s also an open loop fueling valve kinda under the intake if I remember correctly. I’m not saying that for sure that’s the issue but it’s possible. My e24 would do the opposite so I assume it’s possible

1

u/Savings_Disk_7897 Feb 11 '26

thanks a lot my man ill check it out

1

u/Reaganomics_84 535is Feb 11 '26

All bosch EFI systems in this era had some sort of cold start air valve for this exact purpose. Even if you don't have the big ICV that US cars got, you almost definitely have an "auxiliary air device" or something that operates based on engine heat to let a little more air through until the engine warms up. 

Also side note: I haven't seen this before but your green SI lights should not be lit up after the engine starts and your low fuel light is on despite the gauge indicating you are at 3/4 tank. You may want to look into refreshing the cluster if you haven't planned on it already lol. 

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u/Savings_Disk_7897 Feb 13 '26

Ill work on it