Maybe its just a fluke and the two are not interconnected.
On a side note I have a friend who works for shell Canada as a chemical engineer. He was saying that shell as a corporation has done tests and can't really see a difference in knock from 87 -93 octane. He himself only runs the min octane in his audi. But his car isnt boosted, and for me a couple bucks extra seems like good Insurance.
Plus shell does sell its fuel to mom and pop stations.

 

Clean your maf first easy fix if this is it ,electrical cleaner #2 philps and clean away

 

When my MAF is now dead I get annoying hesitation around 2k rpms, is yours similar?

 

My car used to stall at a stop if I arrived with a little gusto. The DME would try to rev the engine to keep it from stalling, but it would not always work. It turned out that the stock F hose had a slit. Found it via a boost leak. Replaced the hose, problem solved. Don't know about running regular gas. This is in CA the land of low octane premium unleaded!

 

Try premium again and you'll know first of all if it's fuel related. Go to a gas station that is creditable in your country.
It might be due to the fuel, higher octane detonates under higher compression so maybe you have a compression problem. How many km on your car?

 

No mine is when I'm idling or near idling.. so 1000 rpm or less, it would dip to < 500 and almost stall but usually picks itself up.

Still could be a MAF problem?

 

~55k miles. When you say pressure u mean boost pressure? There is no boost pressure when idling is there?

 

No, I mean internal cylinder pressure. Although I doubt it.
When I had a hesitation/ stall at idle/ unstable RPM problem a year ago it was the MAF sensor that went bad.

 

ARCO is also BP...

Wondering if the actual gas is any different?

While I don't recommend low grade fuel in a TT, lower octane fuel actually makes more power as long as you're not running into detonation..

Higher octane fuel ignites harder and burns more slowly

 

Sam .. its vac leak ... ask me how I know ....

It doesnt stall / hesitate as much anymore cuz of the temp / humidity change ...

Although when it hits January ... you're gonna get lotsa ABS/PSB lights if you dont get it plugged ...

 

I actually find my car runs better on 89 than 91. I'm in Iowa where 87 and 91 are gas and 89 has 10% ethanol. 89 is also the cheapest (this is Iowa, after all).

Maybe the alcohol runs cooler?

 

Anyone catch this? His "regular" is just as good as California "premium" 95 RON is about 91 USA (AKI/PON)!!!11

Sam, your car will run fine at 95 RON. A car runs best with the lowest octane possible without detonation.

 

It's either the below diagnoses or your coilpacks/plugs are due for a replacement... However, switching grades is only a bandaid masking the real issue... I'd be more concerned with addressing it than buying different grades of fuel, especially at the going rate of a 996TT motor these days.

Mike

 

Maybe this will shed a bit of light on what you are experiencing.

And just a bit on my background. I have been in the motorcycle business since the early '70s full time. I build hot rod motors and have been involved in racing on and off since then. In '85 I raced a Honda Interceptor 1000 on the Salt Flats with an official timed top speed of 148.546 MPH. I had the highest speed runs of all the stock bikes that day. More on this another day.

The Turbo has a lower CR than its NA brothers. It therefore can run very satisfactory on a lower octane fuel, regular 85 or mid 87. This is provided it is not under boost. Boosting ups the CR, more boost = higher CR. If you never ran boost, your car would be perfectly happy with 85 octane, and more important, it would actually run better and faster than with higher octanes.

Most people have the actual facts reversed and completely wrong! The lowest octane fuel packs the most punch and has potential to produce the most power. As octane ratings go up the BTUs per liter decrease. Octane is related to the burn rate, and as numbers increase the burn rate becomes slower. For maximum horsepower, you want the fuel to burn as fast as possible and want to run the lowest octane fuel your motor is happy with.

Basicly the design of the combustion chamber and piston crown along with CR and total ignition advance determine the fuel requirements. Pull back the timing, CR or both and you can lower the octane, but potential power will suffer.

Bottom line here, if you were driving your Turbo on a trip cross country and didn't plan on running under boost 85-87 octane would be fine. If you did run up in boost the knock sensors would retard the timing and you would not realize the power potential of the motor. The electronics on modern motors prevent damage from running fuels that burn to quickly. On other than a boosted motor your maximum power will be realized by running the lowest octane fuel that maximum timing advance can be used without detonation.

This was explaned to me on the "Salt" years ago by the late Don Vesco, LSR record holder.

 

Guys, well after a week of running smoothly on 95 RON, yesterday I refilled using 98 RON and guess what, it started coughing again.

@Saint Ari: so it's not weather related.

@Mikelly: no misfire codes so I think the spark plugs are fine..

@Gmendoza: you're right! Our regular gas (actually it's called Special) is 95 RON/85 MON, which is about 90 PON. Our premium (called Super) is 98 RON/87 MON which is about 92.5 PON. So I guess I'm OK with the lower grade after all.
Source: http://www.adnoc.ae/content.aspx?mid=46&tree=43/48/46

While it may be true that it simply runs better with lower octane fuel, I still suspect there is a faulty sensor somewhere causing the electronics not to adjust properly for the higher fuel grade. I've always filled "Super" in my other cars and never had a problem. Hope to get to the bottom of this