Hi all.

A late nite posting, so im sorry if the spelling wanders a bit

VW Polo, x-reg, 1.4 16v. MOT'd and failed emissions, holding a fast idle the engine suddenly gives a cough and emissions go through the roof, co% 2+, hc 600, lambda 0.9

Let it idle and its fine, try the fast idle again and its fine for a few seconds, then gives a cough and emissions go out again.

Ive narrowed it down, fast idle it around the 2700rpm and the emissions go out, bring it down to around 2400rpm and they come back in.

Its the same when you drive it, get it to around 2500-2800rpm and above and you can feel it choking up.

No faults stored and live data is all ok until fault present, when fault is present the lambda sensor stops switching and stays around 800mv, it starts switching again when the engine speed comes down to around 2400rpm.

Everything is indicating the system suddenly goes rich.

Any ideas?

And if anyone is gonna suggest resetting adaptions, sorry but dont, unless you can tell me what channel and why the adaption has gone out. It bugs me when people tell me to just reset the adaptions. Ive always found resetting adaptions back to factory is a temp cure, the fault is still there and eventually comes back. Fix the fault then reset.