2001 Prius Issues

I agree that you should replace the spark plugs now. Buy the correct NGK or Denso iridium spark plugs as listed in your owner's manual.

DTC P0171 means that the system is running lean. Possible problem areas include a leak in the air induction system downstream from the mass air flow sensor (allowing unmetered air to enter the system), a faulty MAF sensor, the engine coolant temp sensor, fuel line pressure, a leak in the exhaust system, the upstream O2 sensor, and the PCV valve and connections.

Good luck.

 

Looking at the codes:

• P0300 - Random/Multiple cylinder misfire detected
• P0301 - Cylinder 1 misfire
• P0302 - Cylinder 2 misfire
• P0171 - System too Lean

I would lean more towards the fuel injectors. Check the connectors and clean the injectors. You might swap the injectors left half with right half and see if the P030x codes move with the injectors. The ambiguity group from Vol 1, pp DI-67, P030x:

• engine wire open or short
• connector
• vacuum hose
• ignition system
• injector
• fuel pressure
• manifold pressure sensor
• engine coolant sensor
• compression pressure
• valve clearance
• valve timing
• ECM
• PCV piping

Then looking at P0171, DI-62:

• air induction
• injector blockage
• mass air flow
• engine coolant temp. sensor
• fuel pressure
• gas leakage on exhaust (??)
• open or short in heated O{2} sensor 1
• heated O{2} failure
• PCV piping

There might also be a leak in the emissions system connected to the manifold letting in air. A stretch, intake manifold leaks are notorious for causing lean mixtures. Rodent damage can not be ruled out.

Bob Wilson

 

I recommend that you carefully inspect the spark igniters while you are replacing the spark plugs, especially the igniters for cyls 1 and 2 (#1 is closest to the passenger side of the car.) Replace the igniters if the body is damaged in any way, or if you see corrosion on the electrical contacts.

If you see rust on the spark plug shell, then you'll know that water had entered the spark plug well which caused the spark voltage to leak to ground, hence resulting in misfire.

Also note that the wiring harness connector which attaches to the igniter terminals has a plastic lock that snaps into place. Make sure that lock is secure when you reinstall the connector, especially when working on cyl 4 where the wiring harness is very short.

 

It sounds like a vacuum leak or hose and/or a leaking intake manifold. The "2003 Toyota Repair Manual", RM957U2, sketch on pp. EC-3 shows two lines feeding after the throttle plate:

• VSV for EVAP - a hose that comes from the charcoal canister.
• VSG for HCAC - a hose that provides vacuum to actuate the hydrocarbon converter.

Pages EC-7 to EC-12 cover the Toyota procedure that uses a vacuum pressure gauge and engine tests. But there are other approaches for testing vacuum lines.

It will probably throw some other codes but it looks like you could pull the air cleaner housing to access where these hoses come in. You might be able to block the 'VSV for EVAP' hose and see if the symptom goes away. If they remain, reconnect and clear the codes.

The "VSG for HCAC" is a special case because it controls a valve in the exhaust to capture startup hydrocarbons. It this system has a fault, the pressure sensor for HCAC should throw a code. Worse, if the valve remains closed, the car will have 'a block' in the exhaust, another bad thing. Still, sensors can fail and there may be a leak.

I would first jack up the car and see if the HCAC can be 'wired open' before trying a vacuum block at the throttle assembly to check for a leak.

Another approach is to use a vaccum pump, auto stores sell a hand-operated one, and see if the hoses with the car off, pull and hold a vacuum. A leak should be evident.

A hard problem would be detecting an intake manifold leak at the gasket. Regardless, you might want to review this general article about intake vacuum leaks:
Engine Vacuum Leaks

Bob Wilson

 

Sorry, it is Volume 2, "2003 Toyota Repair Manual", RM857U2 which covers repair procedures.

It is dreadfully hot out at 2:45 in the afternoon, +95F. When it gets a little cooler and I can put the car in some shade, I'll go take some photos of the area and use my hand vacuum pump to test the two lines. This will give you an idea of how to check the static pressures.

Bob Wilson

 

correct me if im wrong, but if you're getting a misfire, shouldn't you replace the coils?

 

Not yet but we caught some cooler weather (and rain.) I'll try again tonight.

Bob Wilson

 

Owch!

Check with Champion Toyota, they may have the part for a better price. Also, check the Ebay salvage sellers. Send them a PM and they may have one and you can 'do a deal.' It probably works better if you can phone them vs. using Ebay e-mail . . . if you catch my drift.

Good Prius friend Hobbit snarfed the one known bad NHW11 throttle body and did some forensics. I don't have a link handy but it might give you a clue and alternate approach.

BTW, I'm interested in the broken part. Send me a PM if it comes available.

Bob Wilson

 

www.car-part.com now has a number of used throttle bodies for NHW11. In the $200 range, with some claiming tested good function.

 

Bladder??, is that for no splashing/sloshing around?

 

It's to cut down on fuel vapor pollution. I used to wonder how big a deal that could really be - how much fuel vapor really escapes when you fill up - until I thought it through again and saw that every time you pump 10 gallons of fuel into a typical fuel tank, you're pumping 10 gallons of vapor-saturated air out. So it really is pretty significant. In a Gen 1 Prius, you're just expanding the bladder inside the tank, and forcing out the clean air from the space between the bladder and the tank.

-Chap