Poor Idle is driving me crazy!

[Patrick Wong]

Originally Posted by vertex

...I'm suspicious of the computer. The ECU did suffer some damage from the accident, the 5 volt output for the MAF and TPS etc. was wiped. I but on an external 5V regulator to get it working. Its not easy to get another ECU and try it because it needs to be programmed to match the rest of the computers in the car. That is very expensive, and would be the last step.

Here's my suggestion: buy a used engine ECU from eBay. There are many on sale for $200 or less:
prius engine ecu, great deals on eBay Motors on eBay!

If the engine ECU is the only issue that your car has, I believe that the car will start when you replace the ECU, although DTC P0630 will be logged. Then drive the car to the dealer and ask for the VIN to be entered into the engine ECU. That might cost you another $100 or so; however for ~$300, you can be done with this saga.

Originally Posted by vertex

Well, got the car back. It was running worse then ever! The dealer couldn't figure it out, so there was no charge! The dealer ran diagnostics on the computer, and found nothing wrong. My plan is to pull the computer and see if I can fix the 5 volt output...

Its not surprising that the diagnostics would not yield much help, if the engine ECU can't even provide 5VDC output.

[vertex]

Originally Posted by Patrick Wong

Here's my suggestion: buy a used engine ECU from eBay. There are many on sale for $200 or less:
prius engine ecu, great deals on eBay Motors on eBay!

If the engine ECU is the only issue that your car has, I believe that the car will start when you replace the ECU, although DTC P0630 will be logged. Then drive the car to the dealer and ask for the VIN to be entered into the engine ECU. That might cost you another $100 or so; however for ~$300, you can be done with this saga.


Its not surprising that the diagnostics would not yield much help, if the engine ECU can't even provide 5VDC output.

The 5volt output is only for the sensors. I don't believe it is used internally, at least not the exact same 5 volts, since the sensors do work, and they seem to have the correct output range.
I thought you could not start the car at all. However, if only a DTC is triggered, then maybe I will change my priorities.
Thanks.

[Patrick Wong]

Assuming that the engine ECU is the only fault that your car has, I think it is worth buying a salvage unit and replacing it yourself. DTC P0630 "VIN Not Programmed or Mismatch" does not appear in the table of DTC that will result in the ECM entering fail-safe mode. Hence my belief is that this DTC by itself will not prevent the engine from running.

If I'm wrong then you'll have to have the car towed to the dealer. However this plan provides a reasonable and relatively low-cost way to resolve the known bad engine ECU issue. Good luck.

[vertex]

OK, I fixed it! It was NOT the ECU. The TPS needed to be adjusted a little below spec, at 11% to work. I had tried adjusting it before, but it would never go below the 13.5% specification. I took off the TPS and bent the tabs to increase the rotation CW of the TPS at the stop. I drove it about 20 miles this afternoon, and all was well. Thanks for all your ideas and support. I now need to get the AC charged up. If I can find the bottle of oil I bought that went AWOL, I hope to get that done this weekend.
My next BIG project is plug in conversion. I do not plan on purchasing one, this will be a strictly DIY project. I'll comment more about that in the correct forum.
Have a great fourth!

[Patrick Wong]

Originally Posted by vertex

...I have not been able to pass the emissions inspection because of this problem...the engine RPM hunts between 1700 & 2000 RPM when in park, and up to 4000 RPM when in drive...
I had the idea that even though the MAF was new, maybe its output was high, causing the DTC. The voltage does go over 2.2 volts sometimes under these conditions. So, I tried to reduce the airflow through the sensor. The car ran better, much less surging etc. However, I would get a DTC for lean mixture. I tried to reduce the amount I blocked the flow, but I could not find a sweet spot between the points so that neither DTC occurs. The engine is racing when it shouldn't so mileage is under 30 MPG...

Originally Posted by vertex

OK, I fixed it! It was NOT the ECU. The TPS needed to be adjusted a little below spec, at 11% to work. I had tried adjusting it before, but it would never go below the 13.5% specification. I took off the TPS and bent the tabs to increase the rotation CW of the TPS at the stop. I drove it about 20 miles this afternoon, and all was well...

Congratulations for making the car run, even with an ECM that is off... Let us know when you pass emissions inspection.

Also, after you've logged a couple thousand miles, pls tell us what mpg you are realizing (computed by taking change in odometer reading divided by number of gallons purchased.)

[vertex]

I passed inspection yesterday, no problems. I drove the car 110 miles on Sunday, and and got 47.2 MPG on the MFD. As an aside, I drive 2.2 miles to the train station to go to work in the morining, and can make the trip in EV mode. (It is kind of cheating, in that it is mostly level and downhill. I could not go 1/4 mile back in EV, it is up hill.)

[Patrick Wong]

That's excellent, sounds like you've successfully resolved that problem. Nice to know that you can finally enjoy driving your salvage vehicle. Good work!

[jayman]

Sometimes you have to give it the old college try. Very obvious that as the fleet ages, most dealerships won't be any help

[vertex]

Love the car. What a journey! I have started a new thread under PHEV conversions.