Which order to do maintenance in?

Just to minimize the number of times you need to remove things, group thus:

Since the wipers and cowl come off:

3. Change Spark Plugs
6. Clean EGR pipe/cooler/valve

Since the intake manifold comes off:

4. Clean Throttle Body
5. Replace PCV Valve
7. Clean Intake Manifold (Consider installing an Oil Catch Can too)

(Note, you do not need to disconnect throttle body coolant lines for this. Just disconnect TB and lift it off and out of the way.)

This you might want to do in conjunction with the Plugs and EGR. The EGR has coolant lines, and the drain bolt for engine coolant is round back, more accessible with cowl off:

1. Inverter & Engine Coolant Drain/Refill

This you can do any time you've got the car up, say for an oil change, although it should be raised AND level:

2. Transmission Fluid Drain/Refill

 

Pinching the hoses is (mostly) pointless, since when you pull the hoses off the the egr cooler the main source of coolant is above, in the coolers: clamped hoses or not, it all pours out of the cooler, lol. You definitely could drain the coolant first, that would resolve the problem.

What I did when cleaning the EGR, since I was not planning to change the engine coolant: drain about 2 liters from the radiator drain tap into a clean container (preferably marked with a 2 liter line).. This is enough to drop the coolant level below the EGR cooler and a bit beyond it's connecting hoses.

Then when you pull the hoses off nothing comes out. Just be careful when removing the cooler, there's a little coolant trapped in a back corner. Tip it out into your container as well.

After you're done, everything reinstalled, leave the coolant bleed bolt open (it's at the very top, above the cooler), and slowly pour the drained coolant back into the reservoir. Squeezing the big radiator hoses a bit as you go might help. When coolant starts coming out of the bleed bolt, close it, and carry on pouring coolant into the reservoir. It should end up slightly high, and with a couple of days driving will be back to normal.

 

1. Inverter & Engine Coolant Drain/Refill
2. Transmission Fluid Drain/Refill
Very independent of other repairs, do when you are waiting for something to do.


3. Change Spark Plugs
5. Replace PCV Valve
6. Clean EGR pipe/cooler/valve
All these will be easier/possible if you remove the windshield wipers and their tray. Do them together.


4. Clean Throttle Body
7. Clean Intake Manifold
If you search, you will find many threads by unhappy owners who 'thought' they should do these, wait for symptoms of bad running.

 

www.amazon.com/IRWIN-HANSON-53227-Multi-Spline-Extractor/dp/B0002SRG66

 

If it didn't bottom out it shouldn't be very tight. It looks like it is protruding a little and I assume you tried gripping it with something and tried turning it. Next, I would get a small sharp chisel and try backing it out with it.
Another way is taking a Dremel tool with a cut off wheel and grind a slot in it for a screwdriver and back it out.
A little nick in the surrounding aluminum shouldn't be a problem.

 

Item #2 here:

Ignition System for 2010 Toyota Prius | Toyota Parts

Did you see the spec'd torque for that bolt somewhere, and miss that it was inch/pound units, not foot/pounds? Someone did that a few years back.

Good rule of thumb: if it's a small, "locater" bolt, non-critical, just one-hand it with a ratchet wrench, gripping the ratchet near it's centroid. They don't need much torque.

 

I'm having a hard time finding the torque for that bolt, in the Repair Manual. I did find the very similar MAP sensor hold--down bolt spec, it's 62 inch/pounds. Dividing by 12 to get foot/pounds, that'd be 5 foot/pounds. Yeah things like that, just one hand it, snugging it firmly.

I'd like to get a screw driver with 3/8" drive bit on it, they're strangely hard to find in Canada. They're good for stuff like that.

 

What torque wrench did you used? 1/4? Or 3/8?

I’m assuming it’s the 3/8 torque wrench since the lowest you could go was 10 ft. Lbs.

For low torque value bolts, I would use the 1/4 torque wrench since they’re meant for low torque bolts so you don’t accidentally strip them.

 

I would use a 1/4 torque wrench. I know I didn’t put it in the description but I will put it in so no one gets confused, whoops.

But for those small bolts, hand tighten with the tool should be sufficient, just don’t over tighten it since they’re fragile.

And always use a 1/4 ratchet to prevent over tightening the small bolts. It happens to the best of us

 

Something non critical about that bolt I would just take it to the hardware store and get one and maybe a flat washer.

 

The Toyota bolt in the link is 67 cents though. Local dealership, it'd be a buck or two.

 

My repair manual shows 7 ft.-lb tightening torque for the little bolts that secure the ignition coil assemblies. It is great that the OP was able to remove the broken part of the bolt.

Another possibility might have been to drill a hole into the stud and use a small Easy-Out to remove the stud, if it had broken below the surface of the valve cover.