Not the Mass Airflow Sensor

volkswagen

#1

I’ve got a 2000 VW Lupo, essentially a small Golf, with an 1.4 motor, automatic. 40,000miles. The car’s got the symptoms of a dirty mass airflow sensor but, when I removed what the manual said was the air temperature sensor all I saw was the open end of a small metal tube. No mass airflow sensor. The mechanic at the VW dealer was also perplexed as the specs for my motor (apq) says it has one. At any rate, the car suffers from sluggish performance going up even moderate hills and doesn’t get the gas mileage that it should. What else could be causing this? Also, does one need to clean the air temp sensor in the same way as the MAS? Can a dirty air temp sensor cause these symptoms? Suggestions appreciated. Thank you.


#2

There are a whole plethora of things that can cause this. The MAF is only one of many.
The good news is that the car has an OBD2 system. Has the dealer read the codes? What exactly were they?


#3

I think you removed the MAP (manifold air pressure) sensor. I don’t know if they are interchangable but maybe someone put the wrong sensor there. The MAP sensor is in the intake manifold, the MAF sensor is in the air intake duct between the air filter and the throttle body.


#4
The car's got the symptoms of a dirty mass airflow sensor but, when I removed what the manual said was the air temperature sensor all I saw was the open end of a small metal tube. No mass airflow sensor.

Why would you expect to see the MAF after removing the IAT sensor? Does the VW manual for the car say that? To see the MAF you often have to remove the intake air boot from the throttle body.

Most IAT’s look exactly like you say it looked – but apparently mistakenly thought it was the MAF. The IAT is usually a small 2-3 mm diameter cylinder, maybe 1/2 inch long, that pokes into the intake air stream. It’s usually just a thermistor and is very easy to check by measuring its resistance at a known temperature. VW will have the chart showing how the resistance is supposed to vary with temperature. There’s no need to clean the IAT unless it appears to be coated w/gunk. It doesn’t tend to collect gunk though, b/c of its shape. But MAF’s are big clumsy looking gadgets right in the intake air flow & can need to be cleaned once in a while.

I don’t know whether your engine uses a MAF or MAP, but it almost certainly uses on or the other. If VW doesn’t know, well, I guess nobody does. Maybe visit another VW dealer who does know.

In any event, your symptom is not likely caused by the IAT. I wouldn’t focus on that. As posted above, having the diagnostic codes at your disposal is your best bet. Once you get them, post them here and you’ll get quite a few ideas from the Car Talk forum posters.

sluggish performance going up even moderate hills and doesn't get the gas mileage that it should

As a first guess, I’d suspect something from this list

  • faulty spark plug or too wide of gap (definitely consider this if you hear any pinging)
  • faulty ignition system
  • clogged air or fuel filter
  • clogged cat
  • problem with the rail fuel pressure

#5

Worn engine, worn fuel pump, clogged converter are possibilities. A dirty air temp sensor is not likely the cause.

That’s all assuming there is no driveline slippage in the clutch.

Any Check Engine Light or codes set?