Hey all! I'm a new 240 owner as of last month. I've been looking for a while and finally came across one that had a fairly easy life but needed some love. I've taken care of a few preventative things that I had no history for, in the hopes they might fix a couple other pesky issues that I'm almost certain some of you have experienced. I'll start with what I've done:
-Oil Change
-Plugs, Cap, Rotor
-Thermostat
-Air Filter (there was an actual NEST in the air box. It's a miracle the car ran as well as it did.)
-Exhaust from the cat back
-Timing belt done 20k miles ago

Here's the peculiar part. I live in Northwestern Vermont where the average temp for the last month has been in the high single digits to low teens. This car LOVES to start cold. It starts right up without hesitation even at -12F. When I park for five minutes, it starts back up no issue. When I park for 30 minutes to a couple hours, it needs some coaxing. The starter cranks and giving it a little gas helps. Let it sit overnight or for several hours and it starts up with NO hesitation at all. Once it's running, it runs strong and smooth.

I replaced the thermostat because it seemed to be running cold. Sometimes the temp gauge is where it should be, and sometimes it's buried. I thought the thermostat was stuck open but replacing it did not solve the problem.

Some things I've considered:
-If it was a fuel pump issue, I'd expect the issue to happen every time, or even intermittently without pattern. There is a very clear pattern of when it will be a struggle to start.
-If it was the foot valve in the tank to keep the line primed, I'd especially expect this to happen after sitting all night.
-If it was a cold start injector issue, I would expect it to happen when it's cold.
-Would a faulty coolant temp sensor cause this problem?
-I haven't replaced the vacuum valve on the fuel rail yet -- in fact, all of the parts sites say that item it isn't compatible with a 1988 245 but I think it is. I haven't removed the vacuum line to check for fuel smell because I want to be ready to replace the line first.
-The only other remaining thing that I know very little about is the mass air flow sensor. Would that or the air box thermostat cause this starting issue when the engine is warm(ish)?

I'm curious to know your thoughts!

That is just what I pulled out by hand...I pulled more out with the vacuum!

 

You may have a bad fuel pump check valve. If you have 0 rest pressure the engine will be hard to start warm.

Easy to test - before a start attempt when you know it will malfunction - turn the key to the on/ignition position for 2 seconds, this will run the fuel pump building pressure. Repeat that two more times. On the 4th time engage the starter. If the engine cranks right up - you have no rest pressure. The pressure can leak from the check valve, fuel pressure regulator, injectors, or cold start injector if equipped. The check valve is the most common failure, fuel pressure regulator will have gas leaking from the vacuum line if it's leaking down. Injectors leaking will be either missfires or extremely rich mixture.

 

Thank you for the tip! I just tried that with no luck. I had previously ruled the check valve out simply because after sitting overnight it starts right up with no hesitation and I would have expected the line to drain over that time period.