If no change the 35C switch could have failed.
Per Bentley, 35C temp switch provides cold enrichment off idle (2-3 degrees) and, here is the interesting part for you, again at 15 degrees throttle movement.
I think I was not as clear as I should have been. Unplugging the the 35C sensor will make the car surge all the time, even in cruise. With it unplugged the car thinks it is always under 35C, so you get enrichment any time the throttle is moved even a bit like in cruise. You will see this happen on your AFR gauge.
So you are trying to identify whether the 35C switch has failed open above 35C. If failed open, with it plugged in it will act the same as if its unplugged, enriching for 2 seconds every time throttle is cracked or hits 15 degrees in cruise, causing a surge.
Two ways to test. Much easier to see if the car is set to run with O2 sensor unplugged as the lambda system will counter the effects somewhat. But you can still do it with O2 plugged in if thats how you are currently set up. Just have to look a little closer at the AFR gauge.
Leave the 35C temp sensor plugged in, drive til engine above 35C then look at the AFR gauge in cruise. Push the throttle enough to open the off cruise 15 degree switch. Just a tiny bit should be enough. If the 35C sensor is working, there should be no 2 sec enrichment. If it has failed the AFR will drop instantly way down to 12 or so, you feel a slight surge, then after 2 seconds (per Bentley) AFR pop back up to wherever it was. It’s very obvious.
Other way to test 35C temp switch is with temp based continuity while in the car or on the bench. Normally open (NO) below 35C, closed above 35C.
Your comment about warm starting is unexpected.
AFAIK this temp sensor works with the off idle and cruise 15 degree throttle switch. So it would never affect the start, either cold or warm or plugged in or unplugged because you don't on purpose open the throttle for start. Is your off idle switch adjusted correctly? You should feel a click just after sight throttle movement.
Anyway none of this may be relevant but when you mentioned surging in cruise this came to mind as something that could induce that.
Regards