How to set throttle body initial opening? Almost stalls after starting.

[Circlotron]

The car is on LPG but I don't think that changes things in principle. Anyway, when I start it up when cold it starts, revs up but then the revs drop down to zero and it ALWAYS stalls. When it is hot it does the same thing but it manages to =just= save itself and then pulls up to normal idling speed and away we go.

What I am am imagining is the throttle butterfly is closed too far and the idle air control stepper starts wide then closes up too much and there is not enough total throttle opening so it quits. If I pull the IAC hose off the airbox and put my thumb over it more and more I can hear the IAC trying to keep the revs constant but there gets to a point when it will stall.

I would have thought that the main butterfly would be set cracked open just enough to maintain just below normal hot idle with no lights or A/C, and the IAC adds to this as necessary, not being able to close off the air so much that it conks out. Is this right? How to I set/check the right initial opening for the butterfly? 5L donk.

[wortus]

The base idle screw should not need to be adjusted. The idle is controlled by the ECU adjusting the IAC based ont he RPM ie it has feedback from the engine to maintain idle. What the problem sounds like could be due to a faulty IAC valve, partially blocked air passages for the IAC or maybe the ECU doesn't know the throttle is closed off and in the idle position due to a faulty TPS (throttle position sensor).
Also check for any air leaks and faulty purge cannister components (it's only meant to opurge when the motor is hot and at speed intorducing the vapour to an idling engine could make it stall).

[Circlotron]

Okay. This afternoon the car was sitting 4 hours and about 5:30 I started it up on petrol. Mind you this is the very first time I have ever started it on petrol (had the car 2 months) and it started and ran just fine. May actually be an LPG issue. Tomorrow morning is going to be pretty cold so I'll try it again on petrol and see if it behaves. Starting on gas when cold is pretty ordinary. On the second crank (after the first one stalls) you can hear a cylinder fire here, a cylinder fire there, and the cranking speed jumps up momentarily when this happens and after about 4-5 seconds it fires up and all is well. It has a Gas Research throttle body, the one with the sliding metering rod and all these vacuum hoses going to and from it. I think I'll have to read up on these gizmos.

[mischa]

Your not sposed to start a cold car on gas, even worse on a cold morning.

[Circlotron]

Did it every morning for 18 years in my 202 HJ. Prime, crank less than 1 second, vroom! It did have a super duper ignition setup though. 8 amps coil primary current and 100 thou plug gaps. The VP one is way wussy by comparison. Upgrade is coming one of these days.

[Defected]

i had a similar issue with mine where the accelerator cable had stretched and somehow caused the tb to close a lil bit, i just pulled the cable back a bit on the tb mount, idles fine now

[Drewie]

In the VN V8 manual it says to run the motor for 10 seconds at 3000 rpm to re-set the IAC valve, maybe that is something to do with it, might be worth a try.
They mention this procedure several times through the manual especially if the battery has been disconnected at some stage.

[Circlotron]

3000 rpm? I thought it was only 2000 rpm so that's a thought. The IAC does regulate the idle properly though so it is working.

What do they mean by resetting the IAC anyway? I thought it would reset itself every startup.

[Cheap6]

It does reset on every shutdown and restart. The forced reset is only really useful if you need to get the thing to idle after removing the IAC valve and moving its position or clearing the ECM memory.

There is no problem with starting on gas other than, particularly in cold conditions, sometimes seeing an extended crank time; no choke on a gas carb and lots of gas volume between the converter and mixer. It's inherent with LPG although there are work arounds with things like feeding higher (than mixer) pressure vapour into directly into the manifold while cranking.

[delcowizzid]

the iac reset is just so the ecu knows exactly where 0 steps or fully closed is after the ecu is reset and its lost its saved data.when you rev it over 2000rpm and it fully closes and cant lower rpm under 2000 it knows its at 0 steps and can then count its way open accurately so when the tune commands 20 steps on hot start up it goes exactly 20 steps from closed as well as lots of other times like when you lift off the gas.