2005 A4 1.8T hestitates when cold
 

I have an Audi A4 1.8T 2005. On a cold morning e.g. 3.5 degrees, the car starts ok and I drive for approximately 2 kilometres. For no reason, the car hesitates and there is no power. When I change gears, the problem is resolved and I can drive again. The problem can happen again and again until the temperature reaches 90 degress and the problem goes away. I have changed the MAF and the tempertaure sensor as I thought that the problem may be linked to these but this did not cure the problem.

Any current or pending fault codes?

I initially changed the MAF and that got rid of a fault code which I think was unrelated to this so there were no faults on the system. That did not work so I then just changed the temperature sensor.

Does your brake light on the dash come on?

I dont get any indication on the dash when the problem happens - no warning lights of any kind. There are no fault codes as well.

What was the fault code you had that cleared with the MAF?

It's odd that you don't have a code-makes it tougher.....it could be O2 sensors, throttle position sensor, crank sensor, fuel pressure....have you tried running it without the MAF plugged in on the cold start to see if it makes a difference? If you know where your o2 sensors are, you could also unplug those and see if it runs better on a cold start.....

It seem to be a sensor issue from what you are describing..or I'm thinking it's the idle control valve (ICV)..because when warmed up you say it runs fine, so O2 sensors would be my first guess, but you don't have any codes which is odd....there are some DIY on how to clean the ICV and test it.

Thanks very much for your help. I will check the O2 sensor but as you say it is difficult when there are no codes. The only other thing to note is that when it is cold at night, the brake lights come on automatically. This is a brake light switch issue which I have to replace so perhaps this is causing the car to lose power when driving a short distance in the cold weather. Thanks again.

That's why I asked earlier if your brake light came on... it will cause that issue as well, the loss of power...

The brake light on the dash does not come on when it happens - I get no indication on the dash at all

Understood. But the brake light switch does cause this issue now and then I've heard. I should have phrased the question better...