As some regular readers here may remember, I've been having problems with my throttle body for over a year now. The car drove without problems for a while, then the tach needle would start jumping up and down erratically, finally the EPC light came on and throttle control disappeared almost entirely. The first time around, the VAG program told me that the throttle body was malfunctioning (sensor readings out of range, motor non-functional, etc.). I replaced the TB last year in January, the car drove fine for about 2-3 weeks, then the same thing happened again. Last year I sent my ECU to APR and asked them to resolder their chip on the board (thinking it might be a loose solder joint). When I got it back from them, the car drove without any major problems for nine months. Then the problems started appearing again at the beginning of December. This time I bought a new ECU (thinking that perhaps my ECU was malfunctioning due to a defect in the main board - perhaps because it'd been worked on by APR and Autothority before them), sent it to APR, and had them modify it again. When I installed the new ECU, the car drove for one day and the problem appeared again.

So I was trying to troubleshoot the issue this weekend (with lots of useful advice from Mat Reid), mainly by following the factory manual procedure (test voltages, test continuity, etc.). All tests checked out OK and the manual's final advice was to replace the TB. But I refused to beleive that it was the TB, since I'd replaced it last year and it still failed.

So finally I decided to take out the current TB, put in the other one, and see whether it would work with both ECUs (the TB that was on there was failing with both ECUs). When I took off the TB I noticed rusty water dripping from the bolts/bolt holes. I put on the other TB and tried it with both ECUs - it worked fine.

So here's my current theory: I have an Aquamist water injection system built into the car that sprays water into the intake, right after the intercooler and I suspect that it's the water which was causing the TBs to fail. In the summer it was warm enough that the water evaporated before it could accumulate. In the winter, however, water mist probaly collected in the TB housing and caused a short in the electronics. This is most likely why the TBs would work for a while if they were left outside the car for days/weeks, but then failed after a few days of use.

Of course this theory could be false as well, but there's a good chance that I've finally found the culprit. If so, I advise anyone who has water injection built in to make sure that they're spraying the least amount of water into the intake; otherwise you might well face a problem similar to mine (if you have a car with an electronic throttle valve) unless you live in a region where it's always warm (but even in that case, water in the TB housing cannot possibly ever be good for it). The TB was of course bolted tightly onto the intake manifold, yet the water still managed to escape past the two metal plates.

I haven't decided yet whether I'm going to reactivate the water injection system again with a smaller nozzle (I think my current one is .7mm which is activated around 5 lbs of boost). But apparently there is an upper limit to how much water you can inject in a DBW car.

 

Hi, I was interested you post, I have an ongoing throttle body issue on Bank 2, RS5 V8. Connectors have been updated as recommended by Audi, worked for a bit, then same code, P2131. Swapped throttle bodies over, code returns on bank 2, so don't think it's the throttle body. Thought it maybe the wiring loom, so have run it's own from throttle body to ECU, but still getting the same problem. I'm thinking it could be an ECU problem? Any advice? Many thanks

 

I have exactly the same issue with a bank 2 intermittent TB fault.
Ive had the TB replaced and the car runs for around 20 miles and then throws up a load of faults and the EPC comes on and goes into limp home mode. When it’s plugged back in it comes up with the same fault. A Mecanic has suggested an ECU issue but hesitantly.
i have now taking the car to Audi and I’m waiting a response.
Is this a common issue?

 

Hi, I'd be interested to know what Audi say to you, I've yet to book my car with their tech team. It has been suggested to me to replace the ECU, but also, been told it could be the throttle pedal sensor issues. Cheers

 

So I’ve just got the car back yesterday and I’m touching wood as I’m saying this but it’s been driving perfectly.
Audi have changed something on the wiring loom to do with pin 47 which is related to the TB.
They said if it happens again they would look at replacing the ECU.

 

Hey there I'm new to this forum. I own a 2009 S3 with a similar problem.
I get a EPC light fault code & car goes into limp mode. VCDS scan comes up with P0121 & P1545.
Replaced throttle body & pedal sensor but still have the same issue.
After some research on other forums im thinking it might be an ECU problem.
Anyone with any experience on this issue?

Car also has a runner flap delete, anyone had any issues with them before?

 

i am
getting the same problems audi s3 2009 throttle body ffs and canbus wiring codes, did you sort yours?

 

Havent fixed it yet. It happens a lot after its rained or ive cleaned it so im pretty certain it is the ECU because of the placement infront of the windscreen.
Hows the repair going for you?

 

mine is similar happens when its rained etc so it could possibly be something to do with my ecu, i am changing the throttle body connector pin tomorrow to see if that makes any difference but it may be hard to tell as it only faults now and then

 

Same here, its very sporadic. i have heard of the connector pins failing, let me know how it goes