Rough idle, slow acceleration and high fuel consumption

[luketanti]

Hi all,

I have a 1998 3 door Polo hatchback. It has been running ok until about a year ago the fan switch failed and the engine overheated. I have replaced the fan switch and also the fan fuse and they work ok now.

But the problem is that in the past year the engine was running very strange. It start no problem in the morning when the engine is cold. Acceleration is slow not like before and if I get stuck in traffic it starts to idle very slow from 900 to 700rpm. Sometimes the rpm falls below 300 and if I do not hit the throttle it will stall.

After reading about this problem I bought a VAG-COM cable and read the errors.

I got these 4 codes


I am thinking that it is a faulty temp sensor but the temp gauge seems to be reading temp correctly.
Here is another screen shot from the ECU and it show that it is reading the sensor.


Should I replace the sensor or there could be another problem?

Thanks!
Luke

[alexperkins]

The temperature sender has two sensing circuits. To me that looks like it's faulty. Get it replaced with a genuine one (copy parts albeit cheaper will fail very quickly

I would also give the throttle body a thorough clean with carb cleaner spray

[luketanti]

Hi. It has been a while now. I have changed the temp sensor with a new one. The error is now gone. But I still have the rough idle issue going on.
It is really annoying. When I'm in traffic I have to keep the throttle pedal lightly pressed but it does not happen every time.
I have check for the error codes and now these codes popped up.


Does this mean a faulty O2 sensor?
I do not wish to buy a new one and the problem remains.

[alexperkins]

Check the wires aren't damaged to the lambda as this is quite common

If they aren't, it'll need replacing

[luketanti]

Can it also be the MAP sensor?
I've read that it can cause rough idle as well.
I will try to unplug the MAP sensor ans see how it reacts.

[alexperkins]

The map sensor rarely fails. That won't be causing the lambda errors you are seeing

[luketanti]

Here is a video of the problem

https://www.youtube.com/watch?v=AXL11N3uypw

[alexperkins]

Thats sounds like a blocked PCV, or the idle valve on the TB is blocked and its choking and struggling to regulate

It doesnt sound very healthy in any case

[luketanti]

Yesterday I removed the air filter and checked the plugs. When I unplugged the first one white ash came out and there was oil all over the plug. The other three where fine, shiny and no oil or white ash. Then I removed the plug and found the crown was covered with black solid sludge. I cleaned it using a wire brush, cleaned the oil and the plug. Re assembled but it did the same thing. Now you mentioned the pcv and yesterday I found oil so it might be connected.

[alexperkins]

Another thing to check is the vacuum hose that comes out the back of the throttle body that goes to the brake servo. This can commonly split either on the rubber section or the rigid plastic section and cause all kinds of odd idling issues