Another problem!

I have an Emerald and VHPD in my S1. I’ve had an ongoing problem with the engine where the idle keeps increasing the longer the engine is running. I’ve altered the map as advised by DVA which helped but still the problem occurs. It can reach up to 3.5k revs when the clutch is dipped. Air must be getting in somewhere surely? Could it be the IACV? I’ve changed the TPS and there’s no air leak at the inlet manifold. All temp sensors are fine. Looking at the map it’s sitting happily at high revs, whatever the load. The problem doesn’t occur at low temperatures, only once the engine is hot does it get worse. Any ideas? I’m stumped :frowning:

That can happen if the idle fuelling is way off as you need more air to compensate, howeber when the engine speed rises to another speed/load site where the fuelling is much better the RPM can soar. It just needs someone with a bit of nous to look at it for 5 minutes.


Hi Dave,

thanks for the fast reply. You may remember I sent you an email about this problem a while ago. This morning the revs were sitting at 4.3k, even with a cold engine, it keeps gettng gradually higher. Could it reach this level even with a closed throttle and how come the problem gets worse even when the map remains unaltered? Would this happen if the TPS value wasn’t dropping and it was overfueling? It might be the wiring rather than the TPS.

I think I need to get it up to DW to have a look at it as I can’t fathom it out.

An engine cannot rev to 4,300 without air, that is how you get the engine to idle, by restricting it’s air supply, without restriction every engine would run immediately to the soft limiter. Measure the airflow through the throttle bodies, if it is coming through them, check the throttle cable isnt sticking or the TBs sticking. Block the IACV feed with your finger, if the revs drop it is the IACV too open. It will be very simple, too much air is getting in somewhere.


Had this problem, mine was sticking throttle bodies - not uncommon on the VHPD - couldn’t believe revs on such a small throttle opening

I suspect this must be it as I’ve investigated the IACV before and it wasn’t that.

Out of interest, what was making your TBs stick and how did you rectify it?

Hi there - a friend sorted the TBs out for me - apparently there is an internal poly bush on the spindle that wears, this allows the butterflies to move across ever so slightly with the result that they are not central in the TB causing them to remain slightly open.

I’ll have to ask him what he did to rectify it tho’- think he replaced the bush with something more robust.