Questions and Answers

Volkswagen Passat Very Poor MPG Q. Hi, I have a 1996 Volkswagen Passat Wagon, with a 4 cylinder gas engine, 5 speed manual transmissions, with about 205,000 kilometers (127,381 miles) on it. A week ago, suddenly the car would crank but not fire. The local shop here in France replaced the box that provides current to the distributor, and now the car runs again. They also put in new spark plugs.

However, now the gas mileage is way off with the price of gas here ($7.38/gallon) that's serious, and at just over 5,000 rpm the engine starts shuddering or coughing, even though redline on the tach is 6,500. I never noticed that before. The mechanic turned the distributor, and that improved the mileage, but it's still not as good as before, and the rev problem is unchanged.

Next, he suggests replacing the rotor, but for some reason not the distributor cap, as the next step. While it looks as if the distributor cap and rotor should have been replaced some time ago, I wonder if replacing either is going to fix these problems. Any suggestions that I can try to translate for the mechanic?

Thanks,
Ryan

A. What I think needs to be done now is to connect a scan tool to the vehicle and check sensor operations. In particular the Coolant Temperature Sensor (CTS), the Throttle Position Sensor and the Mass Air Flow (MAF) sensor. I would want to see what they are doing since they are the most likely to cause the problem.

The CTS should be checked with a cold engine, after sitting overnight. The CTS should read within a couple of degrees of ambient air temperature. Then with the engine at operating temperature with a thermometer in the radiator. Again, they should be fairly close to each other.

The TPS can be checked with an analog, needle type, ohmmeter. A digital can not give you an accurate reading. With the ohmmeter connected and the engine OFF, slowly rotate the throttle shaft and observe the reading. It should show a smooth, steady rise with no bumps, jumps or drops. If it doesn't, then you need to replace it.

Volkswagen issued a TSB, 2499-04, on the MAF. They are prone to oil vapors from the Positive Crankcase Ventilation (PVC) system collecting on the MAF sensor.

Service Procedure:
Clean MAF sensor element and install breather valve kit Part No: 037 198 002

• Obtain radio code.
• Note customer's preset radio stations so they can be reset when done.
• Note time on clock so it can be reset when done.
• Ensure ignition is switched OFF.
• Disconnect Battery Ground (GND) Strap.

MAF sensor, cleaning:

• Remove intake air duct (between MAF sensor and throttle body) and discard.
• Remove MAF sensor.
• Carefully clean MAF sensor from both sides using a solvent based electronic cleaner which is safe on plastics and leaves no residue, such as Part No. ZVW 805001 or equivalent. One can will clean approx. 2-3 MAF sensors.

CAUTION! The MAF sensor film is very delicate. DO NOT touch the film during repair. DO NOT use any harsh cleaners such as carburetor cleaners. Always read and follow precautions listed on cleaner container. DO NOT use compressed air to dry. This will damage the MAF sensor.

• Inspect air cleaner for oil saturation and replace if necessary.
• Reinstall MAF sensor.

Breather valve, installing:

• Disconnect bottom vacuum hose from side of intake manifold.
• Disconnect top vacuum hose from side of intake manifold to fuel pressure regulator.
• Cut top hose 60 mm from fuel pressure regulator.
• Shorten remainder of hose to 50 mm, insert green plastic vacuum "T" between two hoses and reinstall hose to top port on intake manifold with clamp.
• Install previously removed bottom vacuum hose to open port of green plastic vacuum "T" with clamp (this leaves bottom port of upper intake manifold free).
• Install new intake air duct (between MAF sensor and throttle body) and connect to breather valve.
• Install support (A) on fuel line, route vacuum hose from new breather valve into clip as shown and connect to bottom vacuum port of intake manifold with clamp.

Electrical harness, installing:

• Remove lower panel below fuse/relay panel.
• Lower fuse relay panel.
• Remove body plug (approximately 40 mm) located near brake booster.
• Insert harness (with fuse, black and brown connectors) through body panel to inside of vehicle.
• Fully seat grommet into body panel.
• Route brown connector behind fuse/relay panel bracket and insert into center ring of brown ground lug at A-pillar.
• Connect fused black connector to open terminal in black 4 point TV block located above fuse relay panel or clipped to steering column bracket.

Note: If black 4 point TV block has no open terminal replace with Part No. 3A0 937 517 (8 point TV block). When connected, relay should activate with ignition key in the ON position only.

• Reinstall fuse/relay panel and lower panel.
• Route harness with existing engine compartment harness to right side of vehicle behind black plastic harness cover .
• Plug connector into resistor for newly installed valve and tie-wrap harness.
• Connect Battery Ground (GND) Strap.
• Code radio.
• Reprogram customer's preset radio stations.
• Reset Clock.