Rough Start up

[stumpage]

When I start the car it runs rough. I can't touch the accelerator as it will cut out. I have to give it a couple of mins then the car will rev ok. It kicks out a load of white smoke for a few seconds then all is well.
I have changed the plugs, leads, dist cap, rotor arm, coil (ignition service). I have cleaned the, ahhhh can’t remember the name of it, sits at the rear of the engine, conical end that get sooted up. No change.
The thing is this only happens after I have put the car away after a long run and left it a few days.

Any ideas?

[QBee]

stumpage said:

I have cleaned the, ahhhh can’t remember the name of it, sits at the rear of the engine, conical end that get sooted up.

Any ideas?

Stepper motor?

Mine did exactly what yours did after I complained of excessive idle rpm. A restrictor was fitted in the 3/4 inch x 10 inch rubber tube that runs from the air intake by the plenum, via a couple of bends, to a location behind the plenum and just below the bonnet catch. It cured the over-revving at idle, but stuffed up the start up, so that I had to sit with my foot on the accelerator for 30-45 seconds, or the engine stalled. I took the restrictor out and all was well again. Might not be anything to do with it, but if you have 90 seconds to spare, you could pull that pipe off and check it's not blocked. Do you want a photo of it?

[stumpage]

Photo would be good. Thanks.

[Julesprivate]

If it is just white smoke that's most likely just condensation from inside the exhaust burning off. If you'd have said blue-ish i'd have suggested valve stem oil seals as they'd let a little oil leak down and burn off which would foul the plugs on first start up.

TBH mine is a bit rough on first start up on a cold day, it is (like yours) fine if I leave it a minute or two but if i pull away immediately I need to feather the throttle or it starts running on 6/7 (or feels that way at least).
I just drive it very gently for the first 1/2 a mile or so and then it's fine.

I just assume it's the fuel being so cold when injected into a cold manifold that it's not burning efficiently. If someone else comes along with a better suggestion I'll be all ears!

[Alun450]

White smoke? Water maybe, I've had a re built engine new ignition components etc, mine is the same for a minute or so, my Jag used to flood also, don't all large V8's have same issue. Just can't handle all that fuel and cold air! I tend to put it in gear raise the clutch and add tiny throttle, seems to not do it if engine has a slight load, dunno if that helps!

[Julesprivate]

QBee said:

Stepper motor?

That is a good point, the stepper motor has a couple of jobs to do and one of them is to "assist" in cold starts (kinda like a cheap auto-choke). I notice from some previous reading that some people rather than fix a high idle problem will "bodge" it by either blocking the manifold feed tube or disconnecting the feed to the stepper (when the engine is up to temp) and setting the base idle.

That's OK on warm days but creates issues with cold starts AND on overrun when the lack of a trailing throttle setting could potentially lock the rear wheels on an over enthusiastic down change.

It may be worth checking the stepper motor for correct operation... Just because it's clean doesn't mean it works LOL.

You can (despite lots of people saying otherwise) dismantle the stepper...actually it'll dismantle itself if you want it to once taken off the plenum (if you unplug the electrical connector and start the car!).

In THEORY it's good practise to reset the ECU if you've manually adjusted the stepper (i.e. if you've cleaned it properly) otherwise they can get out of synch...

[QBee]

Sorry, Thumbsnap refusing to cooperate at the moment. Will try later. If you stand on the passenger side just in front of the windscreen with the bonnet up, look at the plenum where it connects to the air intake, there is a rubber pipe that comes from the right hand side and goes back, then away from you, and with a couple of bends goes under the bonnet catch and throttle springs and connects to something or other. Its that pipe, it's just a push fit. No clips.

[QBee]

Image is rotated, sorry. We are in the back of the engine bay, just in front of the windscreen, passenger side.

That's the pipe, you will have a second throttle return spring where i have removed one. Plenum is to the left and bottom of the pic. Mesh at the top of the pic is the bit just in front of the windscreen.

[Goaty Bill]

Not much help technically, but mine has always 'grumbled' for being left for a while, (like more than a couple of days). That behaviour exhibited from near new, so I put it down purely to her expressing displeasure at being ignored for a few days.
As she normally made an attempt on my life within the first 2 miles of driving, I assumed that was confirmation of my assumption.
Come to think of it, she normally makes such an attempt every time I drive her...

[QBee]

That's the female of the species for you, it would be even worse if you only drove her at monthly intervals
Fortunately for me, Niggles is male.....