Cold running issues

[Laird Scooby]

Originally Posted by Forrest

The main pump had been noisy since at least 2009. I have almost certainly been running the car with a failed in-tank lift pump for over ten years and 100k miles.

I replaced the main pump in late 2018 with a new Bosch unit. Of course, the new pump became noisy almost immediately. I finally decided to tackle the in-tank pump because of the early stages of this problem; so yes the fault does predate the new lift pump.

It has crossed my mind that the 2018 replacement main pump has worn prematurely because of being used for two years without a lift pump. Especially since I hadn't been aware of it being noisy recently, even before replacing the lift pump. However, I thought the main pumps tend to either work or not rather than exhibit intermediate failure modes. It also seems odd that this problem is only noticeable when the engine is started from cold.

That suggests that (for now at least) it would be reasonable to assume the in-tank and main pumps are doing their job.

I'd be inclined to look at the CTS and the ignition components as suggested. The CTS has two thermistors inside, thermistors don't live forever and after 10 years begin to degrade, it could well be yours has degraded to the point where it's giving problems.