MiMitch

2005 A8L 4.2
the rpm surges most noticeably when the car is coming up to temp, it bounces from about 1300 to roughly 1600 when im just cruising along at 35mph on flat road. clean vcds, its like the car is confused.... any ideas as to what would cause this?

Ottoflo

Fuel filter.

mishar

If you are cruising steady 35 mph and engine goes 1300-1600 rpm it sounds like something wrong with your gearbox rather than engine.

MiMitch

i'll try to pay attention more next time its doing it and see if i can tell whats going on, its done it a few times now, but it's not always as noticeable as it was this morning. i hope my tranny doesnt have a case of the dumb... i hate dumb trannys :P

if it is the tranny..... im sure i'll be posting "where does this piece go" pictures when its time to rebuild, the last couple tranny rebuilds i did went fine ( the last was paired to a 2,000+ hp blown big block) never rebuilt an audi gearbox though

side note.... girlfriends get mad when you rebuild a transition in the living room, you WILL be sleeping on the freshly grease stained sofa...

MiMitch

It did it again this morning, didnt really feel like gearbox, but then again... audi gearbox doesnt feel like any vehicle i've owned before. https://www.youtube.com/watch?v=I2If...ature=youtu.be

Jack88

Good lord, I hope it's not something like that. I'm the one who checked out the car and gave it the go ahead, it didn't do that until a couple weeks after purchase. I'd hate to have missed something serious.

MiMitch

I'll just take a week off and head to Maryland so i can use your garage for a week and eat your pizza If stuff goes horribly wrong, we can take it to sinister

Its not causing huge issue and hasn't gotten worse in 1500 miles, I'll just start saving pennies and plan on fixing it sometime after power tour, after "cheap" fixes are exhausted and a proper hands on diagnostic by the dealership of course... the nice part about "worst case scenarios" ..... it doesn't get any worse, plan on it, and sometimes you'll get a nice surprise.

MiMitch

also, originally i thought maybe it was slipping, but it was far too rhythmic for me not to lean toward air/fuel

i was hoping someone would say "i had this same issue"

since it only does it when its warming up, i'll let the car warm up later without moving, that way the gearbox is still cold while the engine is warm.... in theory... if it still does it, its because the gearbox is cold, if it doesnt do it, its because the engine is warm. not sure why i didnt do that sooner

mishar

When the converter lock is engaged and engine is doing that all car would do the same. So, either converter lock is not fully engaged or that particular gear (probably 6th) clutch is not holding properly. Could be low ATF level or lazy solenoid, but it could be just instrument cluster or some other electronic gremlin. Can you hear that pulsing?

Now you know why MP is irreplaceable.

GradecEngineering

+1 on mishar's advice.

I actually have a similar issue, except mine occurs at all times and only fluctuates 100-200 rpm. I will be doing some data logging with VCDS when I have a chance. Hopefully its just a gremlin within the cluster itself.