A3 problems

[Kilander]

Hello!

I recently bought an A3 8l 1.8T -97 chiptuned to 200hp with a lot of issues. I have fixed all of them but 2

I have no fault codes, I just cleared a "Throttle position sensor; Fault in basic settings" by changing throttle body. I do not have the full version of VCDS so I have not had the ability to calibrate it.

The first problem is that after accelerating and then putting the car in neutral/pressing and holding the clutch the RPM starts to fluctuate between 200-600 and the car can stall while driving. I have recently changed the MAF-sensor. But when I removed the wiring to the MAF while the engine was running, it misfires for a second but then runs well and the problem with the RPM disappears. But since I get reading from the MAF-sensor and that I recently bought it can it be faulty already?

The second issue is that the car is running rich, and it did not pass inspection because of CO-value and low lambda of around 0.97. I have fixed a leak in the exhaust before the lambda-sensor, checked all temp-sensors, changed the MAF-sensor and finally put in new NGK sparkplugs yesterday. I have also tried spraying butane around the engine bay to search for vacuum leaks, but found none. I have also measured on the lambda-sensor and the heating circuit is good and I get a voltage between 1000-500mV

Please, if you have any idea of the cause of any of these two problems please tell me.

Best regard.

 

[Kilander]

If anyone has any idea what so ever please reply. I have completly run out of things to try.

 

[Kilander]

Update*

I cleaned the throttle body, but that did not work either....

 

[Retroman]

The main cause of high CO (which will cause failure at a UK MOT) is a failing/failed/inferior aftermarket/sports, catalytic converter OR the car is over-fuelling and running too rich. A sensor problem can cause over-fuelling but the thing I can't really comment on is the "chip tuning" you've had done and whether that is to blame?

In theory the MAF sensor could be the cause of both your problems - checking this sensor is not that easy without specialist equipment. Did you buy an OE MAF or one of the many inexpensive aftermarket ones from somewhere like ebay?

 

[Kilander]

The main cause of high CO (which will cause failure at a UK MOT) is a failing/failed/inferior aftermarket/sports, catalytic converter OR the car is over-fuelling and running too rich. A sensor problem can cause over-fuelling but the thing I can't really comment on is the "chip tuning" you've had done and whether that is to blame?

In theory the MAF sensor could be the cause of both your problems - checking this sensor is not that easy without specialist equipment. Did you buy an OE MAF or one of the many inexpensive aftermarket ones from somewhere like ebay?

Thank you for your reply

The tuning was made by a well respected Swedish company "BSR" and I am hesitant if that is the cause of the problems. The catalytic converter is stock and I had a look at it while repairing the leak in the downpipe (i cut the exhaust pipe about 20 cm from the cat) and from what I could see it doesn't seem damaged, but I have no idea if it is failed/failed. How can you check that?

The MAF-sensor was bought from the German site autodoc and is really cheap https://www.autodoc.co.uk/stark/7587856

 

[Kilander]

*Update

I realized that the MAF I changed to was not correct for the car. So after purchasing the correct and a higher quality (NGK) the problem with the RPM disappeared.

I haven't measured the exhaust yet, so I am unsure whether or not this solved the problem with the car running rich. Although, a problem which i still have and i think might be caused by the car running rich is that the engine can stall during normal driving. It does not hesitate or anything before shutting of, it just dies. It is hard to roll start it, but it starts quickly when i use the starter. Does anyone have a clue?

 

[Kilander]

*Update

I am now quite desperate to get the car working. I changed the lambda sensor and fuel pressure regulator and filled the car up with gas to 3/4 full.

I think the previous owner mentioned something about the car stalling if it has less than 1/4 tank of fuel, which might be the case because it hasn't stalled on a 15 minute trip.

Though, when I went for the drive, the problem with the RPM came back aprox. 3 times which is ALOT less than before changing the MAF. But it still backfires and smells like it is running rich.


I have tried changing out pretty much everything now, and I need new ideas.

I have tried:
New MAF (NGK/NTK)
New Lambda (NGK/NTK)
New fuel pressure regulator (Bosch)
Looked for vacuum leaks with starter fluid without success
Repaired leak in the exhaust
Listen to all injectors (they are all clicking)
Replaced air filter
New spark plugs


Please, any ideas are welcome!

 

[Kilander]

To add to the previous post, when the RPM starts to fluctuate, the throttle body valve (TB angle) also fluctuates with the RPM