My car has developed a rough idle. Could be coincidence that the current tank is shell nitro

After a running through a full tank of the nirto, I noticed no problems at all, idle was fine, eagerness of the throttle was the same. I did notice a 20mile range difference through the tank. But this was probably due to the warm weather!

Overall I'm happy with it and will use it again.

My car has developed a rough idle. Could be coincidence that the current tank is shell nitro

My bet is on fouled plugs. I have the same problem.

When it's cold it widens injectors pulse (not to mention double. phased injecting to warm the cat up) and with not whistle clean plugs it stumbles. I noticed it goes away after a spirited drive but comes back again. It also doesn't happen when air temp is above 22C and car stood in the sun. I do not think it has anythiong to do with the fuel. It just has more detergents in it, that's all...

Cheers Jabo. How would the plugs become like this?

Wrong heat range, wrong gap settings, wrong AFR at times (too rich), ignition retarded too much at times, plodding along and not giving it a welly - those are easy explanations.

Difficult ones include wrong intake port design, wrong intake manifold design both leading to fuel dropping out of suspension or very uneven mixture distribution within combustion chamber resulting in fuel not burning properly and fouling the plugs. Also wrong head design with not optimal squish areas design might cause the above. Valve overlap too long leading to overscavenging increasiong EGT leading ECU to dump fuel in to cool it - you can go on guessing for a while...

Haha. I'm not worried as the new one comes soon!

I still have some VPower in the tank but I haven't had to use the car for 4 days. Longest I've ever gone without using it. Should start with no problems but I'm betting I'll have a lumpy idle

Martyn, no withdrawal symptons?

None whatsoever. I'm off all this week but if I've needed to go out I've either used one of my bikes or can use the Swift. Weather has been crap today so having a lazy day at home. Plus it's a good way of desensitising yourself to speed. No doubt I'll get back in it sometime and it will feel quick again.

wrong intake manifold design (...) leading to fuel dropping out of suspension .

Unlikely with the FSI series of engines (including TSI) where it injects fuel directly into the cylinder??

Unlikely with the FSI series of engines (including TSI) where it injects fuel directly into the cylinder??

Not really as intake manifold design (and more imporantly ports design) can casue such pressure differences and lack of "swirl" that in certain places fuel can drop off suspension on the combustion chamber of the head. Granted with direct injection you do get better atomisation of fuel and less chance of dropping out of suspension but it also bears its own risk if spray pattern is wrong, which I think it was the case with certain batches of injectors on CAVE motors. The holy grail of combustion chamber design is to achieve homogenised mixture distribution within the whole volume of the combustion chamber while keeping temp gradient as flat as possible.