Cold start 1300 RPM 5 min then 900 RPM 10 min before dropping to 600 RPM

I have a 2017 Ford Edge
Titanium AWD 3.5L V6
naturally aspirated with
39,065 km. I bought it used
17 months ago when it had
32,500 km. Everything was
perfect when I bought the
SUV. Then after 2 months I
noticed oil leaking from rear
main seal. I had it repaired
January 27th 2020..
I noticed when I would start
the SUV in the morning
after it sat overnight it
would idle at around 1300
RPM to 1400 RPM for
anywhere between 4 to 8
minutes, and then it would
drop anywhere between
1100 RPM to 900 RPM and
stays there for about 7 min
to 9 min before finally
dropping to it's normal RPM
at 600, and running much
quieter & smoothly.. I've
brought it in to have it
checked at 2 Ford
dealership but out of 2
times they found nothing.
When summer came along
this cold start prolonged
high RPM problem stopped
completely the moment it
got warmer than 17 Celsius.
In the summer I would start
SUV after it sat overnight,
and within 30 seconds RPM
drop to 600.
As soon as the temperature
got down to 17 Celsius I
started having the issue
again. At 17 Celsius it
begins slightly taking longer
for RPM to drop to 600. As
it gets colder the wait time
for 600 RPM drop takes
longer with each Celsius
that drops.  It wasn't taking
as long as it did when the
weather is colder in winter
months.
The weather is now
between 0 Celsius and 5
Celsius and I have 1300
RPM for first 4 minutes, and
then it drops between 900
RPM to 1000 RPM and
stays there for about 8 to
10 minutes before dropping
to 600 RPM.
The issue was completely
gone while it was summer ,
and now with the weather
changing up here in Canada
it's showing itself once
again.
I've looked around for air
leaks and exhaust but I
haven't found anything yet.
I've cleaned the Throttle
body.
When the RPM drop to it's
normal 600 and I stand in
front of SUV or near, at the
moment it drops to normal
it sounds like the engine is
being dampened or slowly
muffled like the moving
engine parts randomly feel
in mud and slowed down,
as it gets quiet to the point I
sometimes think engine
isn't on if I'm inside the
vehicle Another way to
explain the symptom when
it drops to 600 RPM would
be to imagine engine was
only getting a bit of oil
dispersed throughout and
covering parts, and filling
gaps. Then out of know
where the oil pressure goes
up, and the engine parts get
completely covered
100%....noise, and space
between piston and cylinder
gets filled causing less gas
needed.
I should also mention that
when I plug in my block
heater overnight the engine
will have difficulty starting
in the morning. With block
heater still plugged in i
press the remote starter,
and I hear it crank 7 to 8
times without stopping in
between, and at 8 cranks it
starts. I also tried without
remote starter and getting
in vehicle while block heater
is plugged in, and it cranks
but doesn't start on first try.
Takes 7 to 8 cranks every
time I have block heater
plugged in. I have never
heard of anyone having this
problem.
The other thing I have had
since the beginning is a
hissing noise coming from
underneath vehicle at the
rear...near drivers side rear
tire.  It sounds exactly like a
full propane tank valve is
wide open underneath SUV
near the rear drivers side
tire where I fill up with gas
side. Sometimes it's a low
hiss, and other times it's a
louder hiss. The longer I
drive will usually make the
hiss sound like a high
pressure air leak of sorts.
I've had this since may
2020 when I bought it with
32,500 km.
While driving, if no other
vehicles around, and I shut
radio, and heater or A/C and
I listen to my left rear side
of me I will hear a whine
sound only if my foot is
pressing gas pedal and
accelerating.
If I press gas pedal down
slowly.... The whine slowly
gets louder and higher
pitched. If I press gas pedal
down fast.... The whine just
becomes louder, and more
noticable. Basically
synchronized with gas
pedal. I believe this whine
may become a hiss once
listened from exterior of
SUV.
t's been 9 months since
these symptoms began.
I think it's also important
that I mention in  detail the
rear main seal repair I had
done January 27th 2020 at
Ford dealership, because it
is from that very moment
afterwards that these
symptoms began. Unless I
didn't notice the issues
before. That is possible
since after any repair I
listen and pay attention
much more. Also that was
the first winter that the SUV
has been in my possession.
I'll try to make a long story
short as possible.
The Ford technician who
replaced my rear main seal
ended up breaking 2
exhaust manifold studs
flush with the block. I had a
slight difficult time trying to
get  information on how the
Ford technician removed
the studs. At first he would
run around the subject, but  
he kept forgetting to answer
my question.
So eventually I flat out
asked him if he drilled them
out, and he responded yes,
and didn't say anything
more. I found the whole
exhaust manifold broken
studs thing to be very
strange.... Almost seemed
as though he knew
something but was
confused if he should
mention it or not. Anyway
I've always felt that the
exhaust manifold area in
bank 2 might be a
nightmare waiting to be
unraveled.
The thing that concerns me
is when I dropped off SUV
for rear main seal
replacement I had just
bought some expensive
Gatorback mudflaps that
are custom fit for a 2017
Ford Edge Titanium. I payed
$550.00 and I decided to let
the ford technician Install
them after he is done with
replacement of rear main
seal. Anyway long story
short when I went to pick
up my SUV and I was
walking towards my vehicle
I could ASAP notice all the
mudflaps cricket. So I
ended up taking a closer
look , and to my horror the
technician forgot the bolts
that are placed towards the
inner of SUV. He placed the
bolts that go on the outer
metal frame that are on the
very edge of the rubber.
There was only the very
edge held in place, and I
was able to grab the
mudflap from the inner part
and pull it away from its
supposed place.... basically
exposing  behind the flaps
by simply pulling. When I
seen this I became worried
about the rest of the work
on rear main seal. I went
back in the dealership to
complain, and technician
grabbed new hardware, and
while he is next to the
mudflap, he had to ask me
where exactly I wanted the
bolts. Keep in mind the
mudflaps cake in 2 thick
clear plastic bags. The 2
front flaps with a easy to
read instruction that has in
big black  letters 2017 Ford
Edge Titanium. Then below
this 4 pictures of the tools
needed. Then 4 easy steps
showing all bolts, and nuts
with washers used. Nothing
to throw away. From the
way he did the mudflaps, it
was clear he doesn't care
and is simply going through
the motions and waiting for
payday. He removed the
transmission, PTU transfer
case, exhaust manifold, and
down pipe exhaust. When it
comes to mistakes.....every
possibility is on the list.
From missing gasket, to
forgetting to change
gaskets, and from wrong
bolts/nuts to over or under
tighten can very well all be
possible.
Any help would be greatly
appreciated. Thank you.