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Audi starting problem - lucky
I need some help. My 1991 Audi 100 2.8V6 quattro has developed a problem when starting. Just today I find it fires up OK but then almost immediately cuts out. The problem has never occured before today. The one thing I did different today was to fill her up with Shell Optimax (I have always used premium unleaded). I then drove her a 2 miles home, went in for about 10-15 minutes, came out to start the car and this problem developed. I tried again in 20 minutes - no help. Called RAC - took about 1 1/2 hours - but when he came the car started no problem without any intervention! Late tonight I thought I might try to start it - guess what: the problem has recurred - fires up but cuts out immediately. RAC man told me at the time that a change in unleaded fuel type SHOULD NOT cause problems but he then went on to tell me a story about a friend who had this problem due to a change from super unleaded to premium unleaded.
Audi starting problem - Roger Jones
Just in case it helps:

tinyurl.com/25dt7
Audi starting problem - lucky
I have solved the problem now - the Shell Optimax petrol was causing it. I took the car for a cruise right round the M25 and some way up the M11 to use up the Optimax petrol until the tank was almost empty. I then filled her up with the "normal" premium unleaded. Car starts as normal now. My question is why did this happen? May be this should be moved to the discussion thread as i would be interested in similar experiences.

Incidently I have, in the past, asked at main dealers for this VAG fuel additive mentioned by Roger Jones. Dealers always seem reluctant to sell me the stuff!
Audi starting problem - Aprilia
TBH I don't believe the Optimax was causing your problem - I think it was conincidence.
Your car uses KE-Jetronic, right? I think you have a problem there somewhere.
Audi starting problem - Peter D
I agree with Aprilia, coincidence except for the spelling. Regards Peter
Audi starting problem - Roger Jones
Could it be that your M25 cruise was effectively an Italian tune-up that cleared the problem? What is your normal pattern of usage? Yes, I am alluding to the common short-trip problem, which I have experienced -- that's what the additive cured instantly in my Audi 100 -- and which is the most common cause of similar problems experienced by several friends. I agree with the other respondents that Optimax is highly unlikely to be culprit. It may be something much more complex, of course, but let's eliminate the simple stuff first.

You say the VAG dealers were reluctant to sell the additive to you. Did they refuse or were they just plain ignorant of it, as two main dealers were when I ordered it from them? That's why I always quote the part number (G 001 700 03). Alternatively, could it be that dealers are suspicious of a product from their own manufacturers -- I wouldn't put it past them. I gave a bottle to a friend with a BMW 635csi recently and he was astonished by the difference it made; his car had got clogged up by short trips to the railway station. For what it's worth, my regular service mechanic swears by it too, and he specializes in Audi, BMW, MB and VW.
Audi starting problem - lucky
I agree that the M25 drive was probably an italian tune up. The Audi is used as my second car, hence it is used about twice a week to do 20-30 minute drives. If the starting problem was not a coincidence then I expect the problem to recur in the future whilst I continue to use normal unleaded petrol as long as my car usage remains the same.

Regarding the VAG fuel additive I have read about how useful it is in various threads on this website and thought of purchasing it. One dealer denied all existence of it and another one questioned me at length about why I needed it (for a Golf at the time) and seemed very reluctant to sell me the additive - I just gave up in the end and walked out. Is there any way of ordering the product over the internet without direct contact with a human being!
Audi starting problem - Roger Jones
Just give them the part number and wait with them until they find it on their product database. If it's not in stock, they'll order it. I buy regularly from the St Albans dealers and formerly from Camden Motors in Luton (now closed); they rarely had it in stock but ordered it without hesitation and it comes in next day-ish. I buy in bulk (10/12 bottles) and ask for a discount, which they always give.

Given that both dealers had no knowledge of it in the first instance and also that their respective workshops failed to cure the problem that I cured with the additive on its first application, I am not that surprised that you have encountered such unhelpful and perverse attitudes -- more grist to the "Competence of main dealers -- what competence?" mill.

I recall one of them remarking on the very low MOT emissions scores of my VR6. I told them I was using their additive, showed them the bottle, and they said "that's obviously what's helping, then".

Finally, consistent with my experience, a 20--30 minute drive twice a week is a pretty sure way of creating the problem. Perhaps the Audi is particularly vulnerable to the bad effects of short-trip usage.
Audi starting problem - lucky
Thanks for the advice - I will try next time quoting the part number.