TDI NO Not what she used to be

At the beginning of winter my 2002 Beetle TDI started to have less power and the gas mileage started slipping more than it should due to winter diesel. It continued to get worse and so I got a new MAF and that seemed to help at first but now a month later it has gotten much worse than it had bean. The colder it is the worse it is. If there is a load on the engine forget it. (going up hills is painful). If I am idling and I step on the gas (in neutral or with the clutch in) I will only rev to 3000 to 3500 rpm. What should I try next?

When was the last time that you replaced the air filter?

Well, if a new MAF was something you “tried” as a shot in the dark, and you are now looking for more shots in the dark to :try next" then it will be cheaper in the long run to just take it to a mechanic.

The MAF was a very good guess, they are known to be an issue and would give you the problems you are describing. Have you cleared out the snow screen on the intake?? Its a screen at the opening of the intake, designed to keep snow out if you hit a bank of it, however it gets clogged up over time and can restrict air flow. NEXT when was the fuel filter replaced last?? If its been a long time replace it. Next up would be to have your intake manifold checked, they tend to clog with carbon over time if you take alot of short trips (no fix you must replace). Next on the list would be check the Turbo to make sure it is developing boost… Also on the list is checking the injection pump timing.

TDI’s are a world of there own, you have to find a mechanic who knows there motors backwards and forwards, and don’t count on a dealership to do so. I would head over to one of the many TDI forums on the web and ask your question there.

Air Filter and “Snow Screen” Maintenance - The air filter should be replaced at 30,000 mile / 48,000 km intervals or not more than 2 year intervals. When checking or replacing the air filter, also inspect the screen on the intake of the airbox and clean if necessary (see below).
In some areas, due to high levels of airborne contaminants, the “snow screen” will become clogged so quickly (resulting in power loss) that it becomes a considerable hassle. Many owners have removed these screens permanently with no ill effect other than slightly more frequent need to clean the main air filter element. The total frequency of maintenance may be considerably lower without the screen than with it in place …

On A3/B4 models, the air filter housing is at the right front corner of the car. To access it, first remove the plastic cover between the top of the airbox and the headlight (it just pops out). Unplug the electrical connector at the airflow meter (between top of airbox and the large flexible hose). Pull the clear plastic fuel lines out of the clamp that holds them. Release the four clamps for the airbox cover and pull the airbox cover away to expose the filter element, which can then be removed for inspection. Unbolt and remove the screen which is bolted into the lower section of the air filter housing, and either clean it or don’t bother re-installing it. This screen is very prone to clogging and some owners have found that it is better to leave the screen out and accept the (possibly) slightly greater frequency of servicing the main air filter. Re-assembly is the reverse, but don’t forget to plug the airflow meter in again, and make sure the air filter element is properly seated in the housing at all edges and corners!

On A4 models, the air filter housing is on the left side of the engine compartment. Release the clamps, pull the cover off, and the filter element is right there. Cleaning the screen requires removal of the lower section of the airbox from the vehicle and then removal of the duct which leads to the air filter housing intake.

Why would a Diesel have a MAF?? How many miles on the car?

My guess; plugged up air intake, plugged up exhaust, plugged up fuel filter…

How about the thermostat?
This is something I recommend replacing every 5 years on a daily-driven car.

replaced the air filter and checked the snow screen. No improvement. I think that I need to take it in but I don’t know of a good TDI mechanic in the Bangor me aria. Thank you for your help.

Did you check the fuel filter??

The fuel filter should be replaced every 20,000 miles on this vehicle. Diesels require more frequent fuel filter changes than gasoline vehicles. I have seen performance problems as early as 25,000-30,000 miles due to a dirty fuel filter.

I’m going to go on a worst case scenario, and say that you have been driving the TDI engine rather gently, and you now have carbon build up in the intake manifold.

Common issue, and requires quite a bit of work to clean out, or slightly less work if you just replace the intake manifold with a new one, but possibly more expense.

Here’s a good article to read:


As BC and I said earlier the intake is a real possibility