Rough Idle and ESP light?

EMMI537942

MEMBER
2008 AUDI TT
3.2L
VR6
4WD
MANUAL
140,000 MILES

The vehicle listed above is an mk2. When I turn the car on sometimes it will drop quickly from 800rpm to about 300rpm and rev between those RPMs for a bit and then settles to 800. When I press on the gas above 1,000-2,000 RPMs it does that again but more aggressively from 1000rpm to 300 back and forth and then settles. I have an ESP and check engine light on.

When the ESP fault light came on my cruise control stopped working. Might be related not sure.

When I got the codes read (don’t have numbers) I was told it was an MAF and oxygen sensors front and back same side.

The back one I was not concerned about since it decides to read lean every other month. But the upstream oxygen sensor code is new.

Recently, I replaced the MAF and Air filter because they were dirty and because of the code but it has helped maybe 10-20%.

Seems to get a little better once the car has warmed up. Sometimes it settles at 800 RPMs and other times around 400 RPMs.

Could the oxygen sensor be the cause of the rest of the problem or is it something else?

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,700 POSTS

Hi,

When the engine is first started cold, it is in what is called an open loop. The requirements to run the engine is predetermined and based on very few sensor inputs.

Once it warms up, it goes into a closed loop and that is when the computer uses the sensor inputs to determine optimal operating conditions.

For me to best direct you, the diagnostic trouble codes would be very helpful. However, I will try my best to help.

The first thing I suggest is to check the throttle body/throttle plate to see if there is any carbon buildup on the throttle plate itself.

Here is a link that explains how to service one:

https://www.2carpros.com/articles/throttle-actuator-service

I am basing this on two things. First, the MAF was already replaced, and the air filter was extremely dirty. Also, you have a lean fuel mixture issue. If the throttle body plate cannot fully close, this can happen

Let me know if that helps or if you have other questions. Also, if there is any way for you to have the computer rescanned to get the codes, that would help. Most parts stores will do it free of charge.

Take care,

joe