Bob Petruska

The way that your Q5 is driven has to be a major concern. First it never warms up enough to burn off the moisture in the oil. This can cause rings to corrode.

Your engine most likely also has chronic carbon build up. Who knows what other problems have developed...…………….

expidia

Yes this I'm sure this is true. We've been driving it more on trips now. Another 2.5 hours highway each way (5 hour round trip) coming up shortly. To keep the milage down for resale we usually take my X5 on trips and its bigger anyway.
It will be interesting to see what the newly installed plugs look like after a month of her driving only 2 miles each way a day for her job.

But I tend to think most drivers only use their vehicles for short hops like if they live close to their offices and only jump to supermarkets and shopping malls which are close to home.

If these high compression engines can't take these short hops, might be a good reason to lease for 3 years instead of buy!

apoelistas

Probably your problem is related to the secondary air pump.

Either you have a problem with the secondary air system or carbon build up due to the secondary air pump being disabled????? Maybe as Bob said your car did not warm up quickly ...... that can cause other issues.....

Does not harm to inspect the secondary air system first.

Bob has the technical expertise. I am not qualified to give recommendations.

expidia

Thanks. I'll Youtube how to check that SEC system for carbon buildup. I might be able to do it at the same time I check the plugs. Good suggestion. One would think the dealers computer would throw off a carbon buildup code in that system though.

expidia

We might have isolated another part of my issue. I suggested to my wife before she starts the SUV in the AM when cold to always turn the AC off. So far its not stumbled after two days of doing this. Maybe its the added load of the AC or worse maybe the AC unit (or its clutch)
is going bad?

apoelistas

When did you replace your battery? Probably it is time to do so.

expidia

Hmmm, thats a good point. Even though we are upgrading it in 6 months we need to get through another upcoming northeast winter and a new battery would be a selling point as I always sell our vehicles privately.

Is the battery under the trunk lid like my BMW and it still has to be programmed into the SUV if I change it myself!

what do you think the cost is if a dealer changes the battery? Or they just code it in for me?

It is a good point that my stumbling issue could be related to an electrical power drop especially if the AC is on when starting.

But I would think the dealers $150 computer hook up would indicate that? Maybe not unless I specifically asked to load test the battery.

And I thank you Apoelistas and others who have stuck with me on this thread.

update; a quick check online quotes is in the range of $550 at the dealer.

Bob Petruska

The battery is under the spare tire in the cargo area. Yes, it needs to be recoded into the Q5's power management system. You need the dealer to do this or purchase the VCDS to perform this yourself and need to know what you are doing.
Search this site and you will find a very long post on battery change and coding.

I doubt that your battery has anything to do with the stumble. If turning off the A/C load on the engine reduces the stumble, it just indicates that your engine is a little weak on power at start up and can't handle the A/C loading.

Again your driving habits and the way your plugs look indicate that something is very wrong. I suspect that there is a lot of carbon build up. You need to remove the intake manifold to see this in the intake ports if this is a 2.0T (you never indicated what engine that you have). My driving habits with my Q5 are like your wife's. I live in PA and only drive about an 1/8 of a mile to the post office and back everyday (6 year old Q5 only has 16K miles on it). but every 3rd day I take the Q5 for a 15 mile run up and down 2 mountains and a lot of level road twisties. I do this run manually shifting the auto trans at red line in each gear and a lot of up/down shifting at near red line rpms for the 15 miles. This makes sure that a lot of carbon is blown out. My 2014 Q5 2.0T and trans run flawlessly. Zero hesitation and no rough shifting at both low and high rpms, A/C on, cold or hot weather. I also only drive the Q5 in sport mode as that keeps the rpm's and shifting at a higher range. Yes I sort of beat the vehicle but I learned that after the years of owing 2 VW GTI's, 2 Audi A4's and a now a Q5 that you need to drive them hard to keep them working correctly...……..

There's a thought drive your Q5 in sport mode and with the A/C on and see if the stumble goes away.

expidia

Thanks good info here. Seems like the same for my 40 hp outboard. Many people idle them while trolling for fish and load them up with carbon when outboards like to run the **** out of them!

I might have the battery replaced at a local audi repair shop before the winter as it will be almost 6 years old. I
originally thought I could use a cable that would hold the memory codes by hooking up to another battery while I changed it out for $177 an AC Delco on amazon but further reading tells the battery has to be coded in from the sticker on the side of it.

expidia

Before the winter I will need to change this 5 year old battery anyway.
What if I order the exact OEM replacement: https://www.audioempartsdirect.com/p...0915105DL.html

And used this memory cable that holds the current codes by hooking up to a 2nd battery and the OBD2 port while I'm swapping the battery out . . .

If I did this would I have to still have the new battery coded in?