Engine rumbles at startup

What causes y ford taurus engine to rumbel when it starts up? I have repolaced wires, sparkplugs and the clock where all the wires come in

How many miles on the car?

Could be momentary low oil pressure or worn rod bearings or both.

The car has about 136000 miles on it and when I check the code for the engine light, it always shows #1 cylinder Misfire. And if I run fuel injector cleaner- the system seems to go away for a few days

Whole new set of symptoms.

Inspect the spark plugs. Swap fuel injectors. Check for vacuum leak. Get a compression test.

What year is it and when was the last tuneup?
How’s the maintenance history been?

Rumbling on startup is generally a symptom of a failure to be able to produce a good strong spark on cold cylinders. While your results with the fuel system cleaner suggest a gummed up injector…perhaps more than one, one sticking and triggering a fault code…a good strong ignition system is also important for a good strong spark when cold.

If a customer told me their car “rumbled upon start-up” I would have to ask a couple of more questions to get on the same page,you seem to be right there,what is “rumble upon start-up”?

I interpreted it to mean that throaty, shaking sound a cold engine makes when it’s struggling to get running smoothly. Sort of like an old cold diesel truck makes on a winter’s day.

But I see your point.

I wonder what the “clock where all the wires come in is”. The distributor perhaps?