Polo 9N3 Dune 1.4 16v Dune low on power

[Chris Stuart]

I have a '07 Polo 1.4 16v BUD. I don't have any lights on the dash, but the engine seems really weak through mid revs and is using a bit too much fuel. When I hook up my OBDII there are no faults recorded but when i view the throttle position in real time it doesn't seem to open in a linear manner.

As I press the pedal on the road, the throttle valve seems to open slower than the position of the pedal. eg; 50% pedal = 30% throttle position, 80% pedal = 35% throttle, 95% pedal = 40% throttle, 100% Pedal = 100% throttle.

As you can see WOT does give WOT at the throttle body, but I don't generally drive with my foot planted on the floor.

I am confused why it does this as you would expect the throttle body to open the same amount as the pedal, could it need alignment? I am loathed to take it to the VW dealer for fault diagno$i$ so if anyone has any ideas????

I have only had the car a month or 2, and it did have a leaky flexible section on the exhaust that I have repaired. I can't hear any leaks from the inlet or exhaust manifold. The car starts first time every time and idles smoothly.

I can view the OBDII outputs in real time on the Torque app, but I don't have the experience to tell if the figures are normal or not?

Lambda voltages? Fuel trims? Inlet pressure? What are normal values?

Thanks

[Chris Stuart]

After a bit more research, I have run the Torque app on android with the following results. (Torque app was running with the engine at tick over after a 30min run to bring up to temp)

26883

As can be seen from the STFT and Lambda after (O2 1x2) the engine is running on maximum lean with the STFT maxing out at 25%.

Also looking at the Lambda after it seems to be stuck and very rarely cross counting, which could point to either a faulty Lambda or vacuum leak in the manifold.

As I can't hear any leaks in the engine bay, I'm going to go for a Lambda replacement on Thursday. If anyone has some other ideas please reply.....

[niall campbell]

Sometimes its back to basics.

Hows the air filter ?

Hows the fuel filter and sparkplugs ?

I would be looking at putting in some fuel cleaner in the tank too, as that's your cheapest option.

[Chris Stuart]

No the easy stuff was checked first. New air filter, new spark plugs and fuel filter have been replaced.

I have changed the lambda after this afternoon, but it has made no difference.

I am a bit perplexed at the way the STFT wanders at tick over, and why it seems to go in sympathy to the lambda before.

I am leaning towards removing the intake manifold and having a look for leaks very carefully.

I think I will also replace the coolant temp sensor, lambda before and MAP sensor just to eliminate.

The is also a rattle coming from the intake manifold at low power / decelerating but I cant reproduce this with the bonnet open so have no idea what it is.....?

[Flash2]

Which O2 sensor did you replace?
What length of time does the sample in your screen shot show?

Jim.

[Chris Stuart]

I replaced the one behind the cat, also known as the diagnostic sensor or lambda after. This was partly due to the heater element in the probe not working as reported in my mates VAGCOM and because of the poor power/high consumption.

The screen shot shows a 10 second period, but I am now not sure if it is a red herring as when viewed in VAGCOM. Bank 1 sensor 1 was very active and cross counting just over 1 second intervals, which is quite normal.

I am now starting to think that it may be more intake manifold related as reported in many forums and posts about the oil separator gunking up and effecting the vacuum and/or the MAP sensor.

I have checked the brake servo pipe but it is in good condition and is holding vacuum (as tested by sucking on it!)

Next opportunity I get the manifold is coming off, the throttle body and oil separator cleaned and MAP sensor replaced.

It might all cost me a few quid and a bit of time, but im determined to get this Polo right as it is a lovely little car. I only got it at new year, and I have done less than 1000 miles on it, but I didn't pay much for it, and I think there's lots more life left in her (64000 miles).

It is the Dune version and I like the styling and wheels!

[Flash2]

The downstream O2 (B1S2 - after the CAT) isn't the one that effects the fuel trim but if the heater was faulty it needed replacing anyway. It's the voltage of the upstream sensor that causes changes in fuel trim.
The upstream O2 voltage (B1S1) switching is normal but that on it's own doesn't tell you anything about the mixture. You'd have to check the LTFT too. You can have a LTFT that is at it max rich/lean limit and the O2
will still switch OK even though the mixture is well off optimum.

Jim.

[Rob69]

get a compression test done to check for burnt exhaust valves, common on these engines.