I’m trying to fix this no start condition on my 99 300D, 265K miles. I’m thinking it’s the crankshaft position sensor after replacing the fuel lines-air bound.

The car has been a little finicky to start after running in the past, but always did start after a few tries. This all started 2 Fridays ago coming back from NJ. I got caught in a traffic jam and the engine warmed up to just at the top of the 80C mark and stayed there for about 15 mins or so and then the car stalled. Here's where I am currently.

1st attempt of the day, she will start up w/o issue. It seems that after the engine has warmed up to 80C that the issue comes up. If I turn off the engine, it will crank but not start. It definitely seems to be temperature related. At anywhere between 60-80C the car cranked over, but no start. If I let about 40 mins go by, temp lowers to below 60C, she will startup w/o issue.

I have replaced all the plastic lines to the main filter and IP, except for the return line on the engine side of the IP. I replaced the pre-filter. I replaced the o-ring on the shut off valve(I think my mechanic replaced that a few years ago) and the o-ring on the return line from the IP to the main filter. Lastly I replaced the fuel hose from the feed pipe on the firewall to the preheater on the engine block.

I am seeing air in the line from the bottom of the shut off valve to the lift pump when revving. I occasionally see air bubbles in the 1st line from the preheater to pre filter, but not in the other lines. I've checked for leaks under the shut off valve and lift pump with a paper towel, but nothing conclusive. I hope this helpful and better than "it wont start"

After reading a number of posts here and other forums I’m thinking CPS is the next logical step. Thoughts??