metalhead_79

Have a strange engine cough that occurs almost every time I start the engine.

It starts ups normal and runs at higher revs a few seconds before it settles down to normal idle.
But at some point during this process it has a cough, like the ignition was turned off for half a second.
It quickly recovers from this and it only happens once per startup.

Have others experienced something similar?
Ideas why it does this?

iaflyer

Does it do it all the time, or just after it's been sitting for a few days?

metalhead_79

No, pretty much every time I start it when it's had time to cool down a bit.

iaflyer

Hmm. Mine's a bit noisy on startup if it's been sitting. The longer it sits, the noisier it is. People seem to think it's just lack of oil at the top end during startup.

metalhead_79

It's not that it is noisy. It's that the revs drop really fast like it's getting too much fuel or no fuel almost like it is going to stall, but then the revs return to normal. This just takes under half a second from rev drop back to normal.

Lichtman

Sorry to revive a super old one here, I’m having pretty much the same issue. On occasional warm starts, it starts right up then seems like it is about to stall out for half a second then recovers and is fine. No check engine light and it runs perfectly the rest of the time.
2013 Q7 3.0 TFSI

has anyone found the solution to this?

Sallad

Sounds like it could be something in the throttlebody? As the butterfly is slowly closing, maybe there is a "blip" in the position sensor of the valve and it either stops briefly or jumps a fraction? (just thinking out loud here)

I'd start with a deep clean of the throttlebody then an Adaption cycle.

If that doesn't do anything, take off the intake tube and physically watch the butterfly valve when the car is lowering the idle. See if you can see it jump or move funny. (unless these cars use a bypass idle valve... hmmm. Not sure if they have some kind of "Idle Stabilization Valve" or not?)