Hey lads,

my miss is driving a Skoda Fabia 1.2htp 46kw 2004 and it can't pass NCT test for emissions because RPM won't hold between 2500 - 3200. It keeps moving up and down.
First thing to do was to check throttle body - cleaned it, no joy. Replaced whole throttle body - issue persists. Took it to service and after 4 days got the car back with "we cant fix it, dont know what's causing it".
Diagnostics aren't showing any issue.

I'm really desperate to get this fixed.
Anyone with personal experience or ideas what could it be?

Edited 29 May, 20188 yr by Craael

Burnt valves is the problem, this can be easily confirmed with a compression leakdown test.

Check the brake servo vac hose for leaks (common fault, hard plastic tube cracks at joints), also the flexi hose from the PCV valve to the inlet manifold, and if neither of those is leaky, try clamping off or blocking the hose from the purge valve (just near the expansion tank). 

Thanks for replies. Checked both and all good, but there’s one thing I forgot to mention. The RPMs actually start going up by themselves as soon as you hit 2300rpm on idle.

Check that the core plug is still sealing the bottom of the EGR valve. Assuming you have the 12-valve/64bhp engine.

On 29/5/2018 at 19:19, Wino said:

Check that the core plug is still sealing the bottom of the EGR valve. Assuming you have the 12-valve/64bhp engine.

Checked EGR, all good. 

 

Desperate 

Best have it checked for fault codes. You can buy cheap scanners if you want to do it yourself and don't have VCDS.

17 minutes ago, Craael said:

Checked EGR, all good. 

 

Desperate 

 

What were the results of the compression and leakdown tests?

Oh wait, you've already had it scanned. My bad.