Abf intermitant misfire.

[hasekna]

Hey guys. I'm just sorting my Mk2 Abf to go back on the road tomorow. The engine has recently been out.

It has developed a random misfire of sorts. When starting and returning to idle it will stay at 1500 rpm on 4 cylinders. Then it will drop down to 900-1000 ish on 3 cylinders. When driving it will switch from 4 to 3 cylinders when pressing the throttle down, although somtimes it runs perfect and pulls like a train. Mostly it runs on 3 cylinders though.

This has happened before but it sorted itself out. At the time I changed plugs, leads, dizzy cap, rotor arm ect. Also changed one of the relays can't remember which one but the VW part number is 191906383c.

I've done a search and the vac pipes have been changed ect. Anyone have any ideas? Could it be the throttle position switch?

[danny_p]

cranck sensor most likely

[hasekna]

Yea I can see where your going with that. Are these abf specific, just wondering if I can get hold of another one to try ect.

[danny_p]

just take it out and look at the wire wher eit leaves the sensor itself,  its proably falling apart and that indicates that it is the fault or is very shortly about to become a faut,  a work o warning if the fault is the cranck sensor and you remove it to look at it don't expect it to work if its refitted that normaly finishes them off

[danny_p]

agg uses it but scrappy ones are normaly f**ked anyway, buy new if it's not that keep old one as spare or sell it.