Dodgy idle when starting first time

Bit of an odd one, but sometimes when I start the RR (3.9 V8 Classic on LPG, always starts on petrol) it won't idle (on petrol or LPG). Even giving it some revs doesn't sort it out, it just basically dies if you let go of the throttle. I have tried driving it for a bit as well, but as soon as you come to a stop it will die again.

Weird thing is, if you let it die and then restart it, it is absolutely fine! Even if you start it, it immediately dies and then restart straight away it behaves perfectly, idles perfectly, everything.

Any ideas what could cause it to be unhappy at the first time of the key but perfectly contented second time around?

Could be the idle control valve....

Small stepper motor mounted to the side of the Plenum chamber on top of the engine....

This acts like a choke, by opening a small valve and letting more or less air in to control the idle speed....

There was also a small bi-metal strip controlled valve on the side of the plenum also (not sure if yours would have it due to model year - and I also cant remember what is was called) this would ofthen times gum up and get stuck....

You never know I could be way off, but worth checking.

EDIT: Just looking at RAVE, I don't think yours has this bi-metal controlled valve thingy....as I think it was replaced with the Idle Air Control Valve...small motor on side of Plenum

OK, thanks Saint! Whats the best thing to clean that with, WD40? Brake cleaner? Just weird it sometimes can't idle on the first attempt but is absolutely perfect second time around!

The valve is controlled by a stepper motor and sometimes the valve gets stuck, restarting the car gives the motor a kick and the valve unsticks....

I have heard reports that it should be cleaned carefully, others say never clean it....

I cleaned mine in my 3.9 classic with a brake cleaner and then made sure I regreased the valve shaft etc again afterwards....

Maybe a more senior member may offer better advice, as I have heard in places not to clean the valve out as it could damage it, but that was yonks ago.

Some of those symptoms were happening to my 4.6 P38 for about 2 weeks before the (10 month old) battery died during the last cold snap.

It would eventually start, but wouldn't hold idle properly or rev easily for the first 20 seconds. After that it was fine unless switched off for longer than 30 mins.

Finally it totally died and embarassingly I had to get Green Flag to jump start me with a portable power pack as it broke down in a petrol station by the slightly inaccessible air machine...only a pair of 30ft jump leads would have reached!

As an aside Green Flag membership comes free with the bank account and it's the first time I've ever tried them...impressed to be honest as the van arrived within 25 mins of my call.

Anyway, I asked him to test the battery, alternator and the wiring for me using his fancy tester. Result was the alternator was in rude health and the wiring was in great nick; but the battery wasn't holding any real charge, so he gave me a print-out from his tester and I was straight round to the motor factors with my receipt and some spanner for a warranty replacement.

Battery had a 3 year warranty which to their credit Unipart honoured...not impressed it died so young though.

Anyway - don't overlook the battery, however new...

generall rule for stepper motor iacv fitted to most makes of car is...

when car turned off,ecu stays alive for a few secs,this controls stepper motor,which should open to allow high tick over for a few secs (depends on temp at restart) when car is restarted..

so as yours is dodgy at first start,one would go for it gummed up..yes clean iacv..sod all to lose trying..

now of course LR may not use this standard..law to themselves they are..and i hate the LR v8 and rip them out and fit something decent..

sounds like the stepper,, i clean them with mr muscle oven cleaner first, leave it to soak in for 10 minutes, then finish off with carb cleaner. also worth looking at the plugs and dizzy cap.