V8 idle speed.

[gas mart 1]

Can anyone advise me on a cure. my 4.6 v8 starts easily , smells rich to start off with , this soon clears and it warms up as it should, it revs and sounds good, but the idle speed sits at 1100-1200 rpm from start up, even after the fans have kicked in. I have checked the throttle cable , no problem there..
cheers
martin

[Wedg1e]

Bobby Shaftoe said:

Really it depends on the spec of the engine, in particular the camshaft profile, whilst a stock RV8 will do 600-800rpm idle anything with a high overlap cam will struggle.

Aye, mine sits at about 750-800 but will sometimes go as low as 600 and chug away quite happily... I'm not quite so happy once the oil pressure starts to drop below 1 Bar though.
I run an RPI type RP1 cam, supposedly 'fast road hydraulic' profile.

[v8s4me]

Does your engine have a stepper motor? If so, check it is tight in its mounting plate and there isn't an air leak here. Might be worth taking it out and giving the plunger a clean anyway.

[mrzigazaga]

gas mart 1 said:

Can anyone advise me on a cure. my 4.6 v8 starts easily , smells rich to start off with , this soon clears and it warms up as it should, it revs and sounds good, but the idle speed sits at 1100-1200 rpm from start up, even after the fans have kicked in. I have checked the throttle cable , no problem there..
cheers
martin

Hi Martin

Does the idle drop once warmed up or stay at the said speed?..Up to that point it all sounds normal.
Just closing air off from the plenum will cause enrichment of fuelling..Do you have an adjustable fuel pressure regulator?....Also timing can easily effect idle..What is your base timing?....

[adam quantrill]

Is this 4.6 on carbs, 4CU or some other EFI controller?

[gas mart 1]

Thanks to all for replying . This is what I know about the engine. Its a 4.6 V8D built in 2001 and has covered less than 10000 miles . Its the Lucas 4CU chipped to Tornado E- Drive spec, with a Jag AFM, I have receipts for these. I think the Cam is a Kent M248 I say think because I have the M248 box containing an old cam. The car was taken off the road in 2004 when the Engine and gear box were removed in order to have the gearbox replaced, I bought it in April this year , and have gradually been putting it back together , apart from a good clean , new plugs , oil and coolant, its not been touched. Apart from the high idle speed it does everything it should, including annoy the neighbours. Its not been tried under load as it not mot'd yet, want to sort the idle speed first.
cheers
martin.

[gas mart 1]

Bobby Shaftoe said:

Yeah the 248 is a pretty damn big cam, you'll struggle to get a 800rpm idle with it, especially pared with 4cu. Never heard of the E-drive ecu but i suspect it's a normal 4cu with about 3 different resistors, unless it's one of the adjustables with twiddly knobs on the side.

As i said you can use the hex screw on top of the plenum to try and change the idle; CW lower, CCW increase

Cheers, I will give this a go , when the weather permits.

[gmw9666]

On both my 420SE's they had to idle at 1100 ish due to the cams (old 420 had a very lumpy 234 cam but don't know what's in the current one)

Either way both were set up on the RR and are very happy with a slightly high idle, can't see the problem

[rev-erend]

Wow - M248 .. wild cam

http://www.wolfitt.com/kentcamdata.htm

A fast idle might be the best that you can get but you can try lowering the tickover and see how it goes.

[gas mart 1]

Yeah, that's it, I did get it down to 1000 rpm using the adjustment on the plenum ,any lower and she just coughs and stalls. Mot this morning, first one since 2003.