Hi folks,

I've been on with a YB conversion in my mk1 for a couple of years now, it's finally at the point where it runs and moves under it's own power, however I've got a nasty idle problem that I can't track down.

Here's the full spec:

4x4 head and block, 2wd sump, standard 4x4 internals
4x4 T3 (uprated bearing and cut blades), -31 actuator, standard amal valve
2wd 3" mongoose downpipe and lambda sensor
Full MSD custom loom
Wasted spark with two new ignition amps and a new zetec coilpack, all new plug leads
Closed loop
knock sensor
L8 ecu
MSD Evo 320bhp chip
Standard fuel regulator (set to 3.5bar), Bosch 044 pump, 803 dark greens

It starts on pretty much first turn of the key, it sounds nice and smooth, it doesn't miss or rock around on the engine mounts. It sounds lovely, in fact.

However, it starts with an idle of 1800-2000rpm, it doesn't appear to drop down. And it also 'self rev's every so often, perhaps up to 3000rpm and then back down again, on very odd ocaaisions it drops down to something like normal idle speeds, but very rarely, and only for a few seconds. Sometimes when its changing rpm like this the amal valve can be heard to click, but not always.

What I've tried:

- Fuel pressure check; was slightly high at 3.8bar, dropped it back to 3.5.
- ISCV; original was seized solid, now replaced with a brand new one.
- Throttle cable; thought it may have been catching, so ran with it completely disconnected and back to the stops.

None of that seems to have made a difference. Every single sensor apart from the ISCV and TPS was replaced when I built the engine up.

Is there another sensor than the ISCV that can cause really odd idle problems like these, or cause the idle not to drop to the correct level after just a few seconds?

I did a quick video of the problem this morning - you can hear it revving now and again; at no point in the video did we even touch the throttle:

https://www.youtube.com/watch?v=zSB2...ature=youtu.be