'Hunting' a fault

[Ant_slowpo]

Hello there first post on the forum, but have been lurking for a while and found loads of useful info. I know there are other similar threads about this topic but I've tried everything and still no joy.....

So my 95 reg polo 1.4 8v is hunting (revs jump up and down.) only on the low idle once the car has stopped and sat still for a while and only after it's warmed up a bit.

Wouldn't be a problem but it's failed the MOT because of it. The revs will drop to about 800 then all of a sudden jump up to 1500 then back down.

You can see (when the air box is off) that the throttle body butterfly is opening a little which causes the revs to jump.

So far I've tried the following:
-Water temp sensor.
-Checked for air leaks. I've had everything on the intake side apart and sealed it all back up with sealant.
-Changed throttle body.
-Lambda sensor.
-Distributor.
-Plugs.
-Plug leads.
-Coil pack.
-Checked air filter.
-Tried unplugging the MAP sensor, the tank vapor recirculation valve and throttle body all of which made things worse.
-unblocked the crankcase breather valve.

The only thing that has worked was drilling a small hole in the throttle body butterfly allowing a little air in. The car then compensates by adding more fuel and it idles consistently but still a little high so still won't pass the MOT...

Any input would be great as I'm at the end of my teather with this and it's pretty much last chance for this little polo before it goes to the scrapy.

Cheers in advance, ant

[Ant_slowpo]

Solved this earlier.... It was the distributor timing. Had ruled it out as it was done by a mechanic but was advanced by about 8-10 degrees!