Engine racing following service

I had our '04, 149,000 miles in for PA state inspection and emissions test as well as to be looked at because of a P0505 diagnostic code. The symptom of the diagnostic code was that the ICE would not shut at all. The past few months I simply cleared the code (ScanGuage) and things were immediately back to normal until the check engine light came on again.

Anyway, in response to the P0505 today they replaced the air filter (I checked, it is installed correctly), checked for vacuum leaks (all okay) and cleaned the throttle body. My wife picked up the car this afternoon from the repair shop (independent, but mechanic trained by Toyota for Prius). Upon arriving home she said I needed to drive it because it is acting very strange. We drove it this evening and indeed it is acting strange. A number of times the engine revved up to 2800-3000 rpm when my foot was off the gas, e.g. slowing to go around a corner or even when sitting at a traffic light. The SOC was normal (blue bars), not high or low. It was also interesting, because even though the transmission was in D, the car was not pulling to go forward, e.g. at the traffic light-- in D, engine revving, but car just sitting there as though it was idling or ICE off.

The ICE would shut down and go to battery mode appropriately. However I noticed that the mpg would not go about about 110 when backing off the gas going down a long hill at around 50 mph (engine warm, battery normal charge). Normally this would bump it up to around 200.

This latter symptom of mpg not going about 110 is a bit subjective and we only drove around 20 miles this evening, but I know we did not experience the engine revving before the car being serviced today.

Your thoughts, o wise ones?!?

PA P

 

Thanks Patrick.

1) No warning lights last evening.

2) No DTC code.

3) After clearing the code, don't you need to drive a certain number of miles before the code is able to reappear? Maybe we are still in that code-free zone? If the code reappears I can see if clearing the code also takes care of the revving problem. However, it is revving now and the code is not showing. With the previous problem of the ICU not shutting down when the P0505 code showing, the ICU did shut down during the code-free zone. This makes me think clearing the code would not effect the revving, since it is revving now.

4) I can check to see if the tech checked the electronic throttle assembly as you suggest.

5) If the electronic throttle assembly is functioning okay, is the reflashing something that only a Toyota dealer can do? Cost to replace ECU?

I did search this site before my post last evening, but have searched more since then. I came across this thread--
http://priuschat.com/forums/gen-ii-...9887-ice-ran-high-rpm-no-apparent-reason.html
See especially John1701a's response in post #4.
Could it be this will take care of itself?

PA P

 

I tried this for ten minutes (timed). The coolant temp was at 184° when I began. The engine cycled constantly every 2 seconds between 1400 and 1800 rpm. I turned it off after ten minutes.

Can anyone else confirm whether disconnecting the 12v battery may help?

PA P

 

I disconnected the 12v battery for half an hour and then drove 20 miles. It appears to be okay so far-- no revving and driving downhill where power was not required showed higher mpg. I'll confirm after more driving.

PA P

 

Sorry I didn't get back to confirm after more driving. This is feeling like a long time ago, but I believe unhooking the 12v battery took care of it. We are now at 185,000 miles and still going strong. Putting less miles on the Prius these days since we got our Think City EV.

PA Prius