Engine shaking at cold startup, no codes

Another one

 

Possible early head gasket issue. Hopefully; whomever you bought the car from didn't put head gasket sealer into the cooling system to cover it up, so they could sell her. There's plenty of YouTube videos on this issue and how to diagnose it.
I would hookup a P10 HUD to monitor the engine operating temperature. Normal operations is 185F-210F; running above those temps, will cause head gasket damage. The temp lamp doesn't pop till around 248F. There's been multiple incidents of owners running gen2 Prius with less than half the required coolant. They only find out when they're asking why the heater wasn't working around this time of year. This is what happens when people don't do fluid checks periodically.
Why are you thinking it's an ignition issue, when the problem doesn't happen when the engine is warm?? In my experience, intermittent ignition coils fail when the engine get warm to hot; NOT the other way around. How much oil is it burning between oil changes; because that's going to take-out the CAT; if it's more than 0.50 quart between changes. The electronic ABS system are also know to fail on that model, and your traction pack is approaching end-of-life too.

Good Luck....

 

Your Prius is having classic symptoms of a bad head gasket. Search for bad head gasket in this Gen 3 forum. You will find hundreds of threads to read.

 

Did you get the plugs from Amazon?

Other than that?
Yeeeeah.

Another "Prius Death Rattle" victim.....

Check your coolant regularly and stop driving the car if at all possible.
It's not going to make THAT much difference for a pre-teen car.
You're probably looking at a head gasket now - or an engine replacement later if you keep driving it.

Good Luck!

 

^LMAO^
"frequently resolved by cleaning the EGR & intake manifold and replacing plugs, coils, PCV valve" False hope, waste of time and money. "Loose heat shield?"; wouldn't that rattle all the time and/or whenever you go over a bump?????
Another winner for google AI......

 

See EGR cleaning and head gasket links in my signature. (on a phone turn it landscape to see signatures)

I would concentrate on the head gasket now: Presumably EGR cleaning is long overdue, damage is done.

Borescope inspection of combustion chambers is the usual diagnostic first step, preferably with engine cooling system pressurized (to accelerate leakage. You're looking for evidence of coolant, say beads forming at the head gasket seam, running down cylinder wall, exceptionally clean piston(s) top(s), and/or pooling coolant.

Bottom link in my signature is the full engine section from repair manual.

Attached has parts no's for the Toyota gasket kit (includes head gasket), and head bolts (good to replace).

Also attached is an explanation of an alternate Toyota gasket kit. Bear with me, I believe there are two kits, and one is more complete, has items for a full engine rebuild. The two kit part no's are:

04112-37254

04111-37315

If you google "04112-37254 versus 04111-37315" the AI summary is pretty good I think. Apparently the latter (04111-37315) is more complete, and now has a revised part no:

04111-37316

 

A Prius head gasket leak fools many "good" mechanics.



The op's symptoms are 99% head gasket. Coolant loss is not obvious at first; it can be weeks or longer before loss occurs. Combustion gas tests are negative for a long period. Compression tests will always be negative.

A proper borescope test on a cold engine with the coolant system pressurized is a test that may show positive.

Car Care Nut HG Borescope at 660s

The real question is what to do about it? A simple head gasket job is rarely done by pros or dealers on this engine due to comeback warranty expense.

A rebuilt or JDM engine is a solution if the car is worth it.

 

That elephant needs to roll-over in the middle of the room to get acknowledgement

 

Oil burning is another big issue on these engines and needs to be addressed with revised parts you should get with a good rebuild. Again most average shops don't know this.

See this post and the post following:
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