Poor Idle is driving me crazy!

[vertex]

I bought a totaled 2006 Silver Prius last summer. It was hit in the front drivers corner. Airbags did not deploy. Someone had removed parts before I got the car. Drivers fender, hood, radiator support, radiator, condenser, fan, TB, air intake, storage bottle, pump, & coolant valve were all replaced. Everything was new except the radiator and the TB. Some of the connectors on the transmission were broken, they were replaced. I repaired everything, and had the salvage inspection etc. I have not been able to pass the emissions inspection because of this problem. The car seems to drive fine, except under the conditions I describe below:

The main symptom is that when the engine idles (that is not shut off, not driving wheels, and not charging the battery) the engine RPM hunts between 1700 & 2000 RPM when in park, and up to 4000 RPM when in drive. This occurs when the engine is in the ultra lean mode, O2 is 0.015 volts. Once the engine warms up to over 158 F, the P0101 DTC occurs. Otherwise no codes.
I checked the MAF and it looks new (as it should, since it is). I checked for vacuum leaks, couldn't find any. Gasket under TB is new. I checked the 3 vacuum ports, and they all seem fine also.
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.

I think that I am looking in the wrong place, but don't know what the right place is. I doubt that the MAF is bad, but maybe I should change it ($$), or the ECU ($$$$$$$). I have the Autoenginuity scantool with the Toyota package.

Also, maybe someone has an idea how I can get it past inspection, so at least I can use the car while I try to figure this thing out!

Thanks in advance for all your help!

[Rokeby]

Your situation sounds somewhat similar to this very perplexing vacuum
leak problem that was discussed on one of the CleanMPG,com Forums

Hope this helps.

FWIW, this thread also discusses some incredibly strong user support by
the SccanGauge folks.

[vertex]

Originally Posted by Rokeby

Your situation sounds somewhat similar to this very perplexing vacuum
leak problem that was discussed on one of the CleanMPG,com Forums

Hope this helps.

FWIW, this thread also discusses some incredibly strong user support by
the SccanGauge folks.

Interesting, I have to check where that is located. There was some minor damage behind the inverter where the brake cylinder is.

[vertex]

I can't locate the hydro booster in the shop manual. It mentions it but does not show where it is. Anyone know which hose is the vacuum going to the booster and where the booster is?

[Patrick Wong]

The Prius braking system does not depend upon engine vacuum, so that should not cause your issue. The brake pressure accumulator pump is electrically powered.

DTC P0101 does point to the mass air flow meter. A few thoughts for your consideration:

1. Are you sure that the installed MAF is the correct part? The Toyota part number is 22204-22010. Any problems with the wiring harness connector?

Further, the Toyota repair manual provides info about how to diagnose a failed MAF vs. engine ECU in the discussion about DTC P0100, P0102, and P0103. Although your car doesn't register those DTC you may find the troubleshooting procedure relevant to your situation.

2. How about the O-ring, was that replaced with a new part when the MAF was replaced? The part number for that is 90099-14141. Are the two screws that attach the MAF secure?

3. What about the metal clamp that secures the air cleaner housing to the throttle body. Is that secure? Any cracks in the air cleaner housing or the intake manifold downstream from the MAF?

4. Have you attached a vacuum gauge to an engine vacuum port to see what vacuum is produced by the engine?

5. Have you checked the voltages at the engine ECU to see if they are correct? The Toyota repair manual provides info about this, for example p. 05-370 of the 2005 repair manual explains how to verify voltages at the ECM. Voltage is provided via IG2 and EFI M relays.

[dogfriend]

I would check carefully for vacuum leaks. Your "idle" speed (no load in P) is a lot higher than what I see with the Scangauge - I usually see 1200 - 1400 rpm. The Prius does not have an IAC (idle air control), but if extra air is leaking in that is not metered by the MAF, that would explain your high "idle" speed.

[Patrick Wong]

Originally Posted by vertex

... It was hit in the front drivers corner. Airbags did not deploy...TB, air intake, storage bottle, pump, & coolant valve were all replaced. Everything was new except the radiator and the TB...

As the throttle body came from a salvage vehicle, is it possible that the wrong part number was installed or that the TB is defective?

I agree with Jason that you need to search very carefully for a vacuum leak. Since the original TB was damaged in the accident, is it possible that the intake manifold has a crack somewhere?

[Rokeby]

Originally Posted by Rokeby

Your situation sounds somewhat similar to this very perplexing acuum
leak problem that was discussed on one of the CleanMPG,com Forums...

Originally Posted by Patrick Wong

The Prius braking system does not depend upon engine vacuum,
so that should not cause your issue. The brake pressure accumulator
pump is electrically powered....

Patrick,

Thank you for making this crystal clear.

In my post I was trying to suggest that the problem here might not be
in the vacuum hoses and their connections, but rather a leak in some
piece of equipment typically presumed to be airtight.

Originally Posted by Patrick Wong

I agree with Jason that you need to search very carefully for a vacuum
leak. Since the original TB was damaged in the accident, is it possible
that the intake manifold has a crack somewhere?

All you guys are far more knowlegable in automotive engineering in general
and Prius-specific trouble shooting than I am. Well, I'm here to learn. There
seems to be a general consensus that the symptoms point towards a vacuum
leak. As an aid to my education, can you help me/us understand more about
this?

In the OP, it is stated that there are three vacuum ports on the throttle
body, TB. To what pieces of equipment do they lead? You've said it's
not to the brake system. And while I've still got a lot to learn, I know
it's not to the windshield wipers.

Where then do they go? One to the PCV valve and...?

[Patrick Wong]

Originally Posted by Rokeby

... There seems to be a general consensus that the symptoms point towards a vacuum leak. As an aid to my education, can you help me/us understand more about this?

In the OP, it is stated that there are three vacuum ports on the throttle body, TB. To what pieces of equipment do they lead? You've said it's not to the brake system. And while I've still got a lot to learn, I know it's not to the windshield wipers.

Where then do they go? One to the PCV valve and...?

Hi Rokeby,

If you open the hood you will see a decal that shows the engine vacuum system. Note that there's one hose that connects to the vacuum switching valve and a purge port. The latter provides vacuum back to the fuel tank HC emissions control. See
Automotive Training and Resource Site
Look for the Technical Article, Hybrid13 Fuel and EVAP System, page 3-5.

Also, if you take a look, you will see a port that is covered by a rubber plug. This would be a good place to connect a vacuum gauge for testing (or your old-fashioned windshield wiper motor... )

You are right in identifying the PCV hoses as another potential place for a vacuum leak, especially the hose connected below the throttle plate. Other common places for a vacuum leak include the oil filler cap (if the rubber O-ring has failed or the cap is not fully tightened) and the oil dipstick not being fully inserted or with a bad O-ring.

If the OP cannot find the leak, then I suggest physically removing the intake manifold and carefully inspecting for a crack. Fill the manifold with water if necessary and see if any leaks out. Use all new gaskets when reinstalling.

[vertex]

Originally Posted by Patrick Wong

Hi Rokeby,

If you open the hood you will see a decal that shows the engine vacuum system. Note that there's one hose that connects to the vacuum switching valve and a purge port. The latter provides vacuum back to the fuel tank HC emissions control. See
Automotive Training and Resource Site
Look for the Technical Article, Hybrid13 Fuel and EVAP System, page 3-5.

Also, if you take a look, you will see a port that is covered by a rubber plug. This would be a good place to connect a vacuum gauge for testing (or your old-fashioned windshield wiper motor... )

You are right in identifying the PCV hoses as another potential place for a vacuum leak, especially the hose connected below the throttle plate. Other common places for a vacuum leak include the oil filler cap (if the rubber O-ring has failed or the cap is not fully tightened) and the oil dipstick not being fully inserted or with a bad O-ring.

If the OP cannot find the leak, then I suggest physically removing the intake manifold and carefully inspecting for a crack. Fill the manifold with water if necessary and see if any leaks out. Use all new gaskets when reinstalling.

I checked both the PVC hose, and the other hose. The PVC valve seemed to work correctly, and the one going to the purge was OK up to the valve next to the engine.
Maybe I can disconnect both, plug the ports, and see if the car idles OK. I expect other DTCs, but at least that would let me know if the leak was there.
I got the TB from Autobytel. They only sell Prius parts, so it is probably not the wrong one. However, the TB position sensor was bad when I got it, and I had to replace it. I checked the replacement one, and it was OK. I bought a new air intake/filter assembly that comes with the MAF in it, so the part must be correct.
I set it up for 14% reading on the position with the ICE off. I looked at the intake manifold, and did not see anything amiss, but it could be there or the gasket. The concensous seems to be Vacuum leak.
I tried the propane trick, but didn't come up with anything. Even puting the propane into the aircleaner didn't have a noticable effect, so I'm not sure how well this works on the Prius.
One thing I don't understand, is why is the RPM higher with a leak?