Won't always start...

#1
Hello. I hate for my 1st post to be a question like this, but I have been fighting with my stepdaughter's car for a month now and I am at my wits end.


She has a 2012 Corrolla. Lately it has picked up the nasty habit of not starting every time you wanted to. It seems to start more reliably when the engine is cold, but it is not a guarantee.

Additionally, the tachometer has developed a bit of a twitch. It seems to randomly fluctuate up-and-down about a 100 rpm. This is not just a feeling gauge, as the engine sound actually does change with the fluctuations come up both while driving and while rubbing it in park or neutral.


I have replaced the Crankshaft position sensor and verified that all of the wiring and connectors between it and the PCM are intact.

I also diagnosed and replaced a weak fuel pump. While that did improve the overall power the car has, it has done nothing to remedy the random no start issue.

It behaves as if something is affecting the fuel trim. My operating theory is that without a good RPM signal, the computer is playing it safe to the point of paranoia and refusing to fuel it at all. The CPS is just fancy magneto, so if it is crapping out at high temperatures, that would explain why the car starts more reliably 1st thing in the morning then it does after it's been driven around for a while.

I have noticed that if I just stay on the key long enough, and I mean 30 seconds or more, it will go ahead and start about half of the time, but I don't like putting that kind of stress on the starter.

Anyone else ever had this issue?
 
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