Start-up engine knock; disappears after 30 sec

Most likely your engine is hosed (bearing/rod etc)...I just bought a car with 266k miles same symptoms and was throwing misfire codes. I replaced the ICE and all is well. Good used Prius ICE's are only a few hundred $$, not worth opening them up IMHO.

Just drive yours till it grenades then replace the ICE. Won't be any cheaper if you do it sooner than later.

 

You have an opportunity to try something I heard on "Click and Clack" the NPR program . . . the various miracle additives. One 'shade tree trick' is to try a heavy grade oil. But in the meantime, look for 'opportunities' and possibly scheduling the engine replacement at a time and place that matches your schedule.

I am a little uncomfortable with not trying some standard engine diagnostic tricks. See if you can get cylinder pressure reading. Also, it may make sense to take the valve cover off and look for unusual cam wear. Possibly swap injectors and plugs into different positions . . . all are long shots.

If it is rod, piston pin, or bearing knock, it is just a question of time. The engine is hammering itself apart from the inside. Fortunately, the control laws are running the engine about as 'softly' as can be . . . unless you are accelerating up hills and mountains.

Bob Wilson

 

Is this the best you can do?

It could be something as simple as bad spark plug: http://www.aecs.net/techniek2012/March%20prius.pdf

 

Check for a bad coil,or in my case had some water that had leaked down the coil tube and did almost the same thing...

 

This is a good one too. Anything that gives a temporary misfire.

 

You might give these East Coast folks a call in the morning:
Auto Careers Development Center - Hybrid and Electric Vehicle Repair Training

They have a web page of recommended shops but sometimes the updates lag:
Hybrid Shop Finder | Auto Career Development Center

GOOD LUCK!
Bob Wilson

 

I have something simular when I start my 01. Only it lasts about five seconds on startup. Seems to only happen when there has been a signigicant outside temp difference from the car's last run time. For instance, when I shut down the car and its 50 outside. Car sits over night and I start it when its 18 degrees in the morning. It sounds horrible but corrects itself within seconds. I figuring this is some sort of timing adjustment that is made by the car to compensate for the outside temperature.
I don't know if its related to what you're experiencing. 30 seconds is a long time.

 

Interesting, this sounds exactly like the infamous 3gen knocking issue that is basically water condensation in intake manifold that shorts spark plugs and produces misfiring. I was able to duplicate the issue in mine by simply disconnecting one of the ignition coils. Check my video on youtube. Knocking is produced at 1:10. Is that what you are talking about?

 

It is that same knock. It starts with the intense knock and then fades away quickly. Again, this only happens durring those big temp changes. If the temp is within 20 or so degrees, it doesn't seem to happen. I'll see if I can record it with my phone one of these mornings to share