dentedrings

I have a 09 Q5 2.0T S-Tronic and sometimes when it is warm and you start it will stall shortly after and it will not start again until the engine has cooled down(like half way down the temp gauge). I have done a engine rebuild because of oil consumpion but the problem with stalling has persisted. For example last time this happned the car was warm and started with no problems, turn of the car and removed the key and then started the car again and after 5 seconds the engine shuddered to a halt. Tried to start again and the rpm jumps up and down the entire cars shakes for a few seconds until the engine stalls. If it drive away directly after start and keep the pedal to the floor the car can splutter and jump around for 10-15 seconds before the car runs fine again. A couple of times I have tried revving the engine after start to keep it going but that is not always successful.
Also sometimes when your rev the engine in second or third gear at like 4-5k rpm is loses power for a split second making the entire car lurch forward before going on like nothing happned.
I have had the car at the shop several times but they say that they can't help me if it doesnt happen when they have the car. So any ideas?

BumblebeeQ5

That all sounds like syptoms of a busted High Pressure Fuel Pump. Take a look at my post for all the details:

https://www.audiworld.com/forums/q5-...ildup-2911373/

I literally just had to get my Q5 towed to the mechanic as I was waiting for my HPFP to get in and it had all of the things you mentioned just before it failed completely. As the above post talks about, might as well get them to take a look at the spark plugs and fuel injectors at the same time. As my mechanic explained to me the defective HPFP have issues with getting enough pressure through them which is causing the rough starts and idles and erratic RPMs. In my personal opinion, if it is actually the HPFP and not something completely else, your HPFP is probably weeks if not days away from failing completely.
But again it could be 100 different things, but that is the most likely thing from what I have read and experienced. Bring it in to a shop and tell them to look at those things first and good luck.

BumblebeeQ5

Literally everything you described I experienced. When a mechanic hooks it up to a computer everything will show up normal. So that is why you will have to point them in the right direction.

dentedrings

Actually the mechanic found warnings for low fuel pressure in the computer and he said "I wouldn't trust the car with this (warning)", but then when I came back with the car they changed their mind and said it wasn't a problem. "You don't just change the fuel pump" they said and then I had to drive of with nothing done to the car. It also logged missfires but they said that was normal.

My car always start fine when it is cold tho. But I do feel like the car behaves differently each time I start it. Sometimes its smooth, sometimes it shifts rough. And before the engine rebuild it was worse but that is just my opinion, the mechanics have never thought there was a problem with the car. I had a A3 with the S-Tronic 2.0T before this and that never had these issues and I would think that they should feel about the same.

Redd

"It also logged missfires but they said that was normal."

Misfires, by definition, are an abnormal event and indicate there's a problem to be fixed. Any mechanic that says otherwise, needs to be sent back to tractor school and kept away from fuel-injected cars.

BumblebeeQ5

Just got my car back after replacing the HPFP. It operates like the first day I bought it. It starts up right away and goes right to 800rpm. This difficulty to start and rough idling I'm almsot sure it'll be HPFP. You should see if there is any fuel leak somewhere. And also It takes like 1-2 hours to replace the HPFP.

dentedrings

I took it to another shop and after they said directly it was the hpfp that is the problem. They also said that with this problem i should not drive the car so they are keeping it, quite a difference from the other place that couldn't find a problem. Now I don't know yet if they are right because it hasn't got replaced yet but at least they found a problem. They say it will be a $1000 job whitch seems kinda high from the other estimates online that I have seen but if it fixes the problem.
After reading up on the hpfp online the "follower" seems like a dangerous problem that can cause engine damage, also the fault code one video I watched about this problem sounded like that exact same that the mechanics at the first place found but said it was no problem (rail\fuel pump low pressure)...

dentedrings

Turns out to be the normal fuel pump not the high pressure one, it was only outputing one third of the pressure it was supposed to. Apparently the computer did not log any errors for this and it was only found because the car died when the mechanic was driving it in the shop and he thought it can only be the fuel pump if there are no errors in the computer. He messured it and it turned out to be faulty. So far it starts every time now so happy days.