Coolant service--intake manifold?

I took my 09 4.0 tacoma in for a couple of things, including a coolant service and replacing radiator and heater hoses.

It ran rough and threw codes when I picked it up, so they took it back in and checked it out. They think they pinched a gasket when reinstalling the intake manifold,causing a vacuum leak. They're fixing it.

I know there's a coolant bypass pipe under the intake, and they told me they take the intake manifold off for the coolant service.

Can anyone clue me in to why removing the manifold is necessary for a coolant service? I'm perplexed.

 

They musta broke something or dropped something under the intake. No reason to touch it when doing rad hoses or a coolant drain/fill

 

You happen to remember what the codes were?

 

Oh wait, I missed the part about heater hoses.. maybe the heater bypass pipe broke or the hose was stubborn and wouldn't come off. I'm trying to picture how buried the heater hoses are back at the firewall but I'm not that familiar..

 

PO171 and PO174, bank 1 and bank 2 lean condition.

MIL and VSC malfunction lamps both illuminated.

 

I think the hoses for the heater core are over by the brake booster.
I think something got let unhooked.

No idea why they pulled the intake?
Weird?

 

All I can think of is maybe they replace the coolant bypass pipe when replacing the hoses. It sure seemed like the service manager said it was part of the coolant service though... Very puzzling.

 

man what
Coolant service

take a pan underneath
Drain the coolant

put new coolant

and if you wanna get real fancy
Instead of only draining the radiator
The engine block has two drain bolts as well, by each exhaust manifold.

 

So, the situation seems resolved, but it's still bizarre.

Disassembly revealed no apparent vacuum leak. They continued diagnosis and found what looked like cloudy, bad gas when they took a sample from the fuel trail.

They drained the tank and put a few gallons of fresh known good gas, and after stumbling for a bit it started to run smoothly. So, it was the bad gas.

But the tank was almost completely filled (over 18.5 of 21 gallons) at a relatively new station of a well reputed brand. There's no dirt on the fill tube, so it doesn't seem like it was a prank. I've never had any fuel problems before, so this is narrowing it down to that specific tank.

I'm surprised the VSC malfunction light illuminates for overly lean trouble codes.

I filled it with a different brand gas and a bottle of Techron. I've driven about 40 miles since then with no lean conditions, codes, stumbling, or misfires.

 

Did they charge you for diagnosing it?

 

Out of curiosity, was this preventative maintenance or replacement was required? Curious as my 2010 with original radiator ages.