Idling and revs

[Russ68]

This is more an irritation than a genuine fault, I suspect / hope, but input would be appreciated. Since I competed the service, including replacing the 6 plugs, coil packs and inlet gaskets, the revs are slightly erratic.

 

Occasionally, she will not return to normal idling, when moving or at a stop, and she'll sit at c1100rpm. I just read she's designed to run at a fast idle when moving to improve the manual gear changes. But if this is the case, shouldn't she then drop to normal when actually stopped? If I reboot (i.e. turn off and on) she'll generally return to normal.

 

Also, when revving, the revs don't descend as quickly as I'd expect, they just seem to hang slightly on the way down, as if some fuel is still getting in despite the throttle not being pressed.

 

Any ideas what these issues could be? Could I have not achieved a perfect seal when reassembling the inlet manifold, or otherwise slightly clocked it up? Happy to strip the manifold off again as I fancy polishing it up which should look pretty special. Or is there any other adjustment or fault finding I can do to isolate the issue?

 

Thanks :)

[Raistlin]

Not used to petrol engines these days Russ, but, are there vacuum pipes coming off the manifold? From my limited knowledge of petrol engines, if there was a leaky hose it might cause the fluctuations you are experiencing.

 

Just a thought.

[Russ68]

That's a very good thought Paul, it could be that and I'll have a look! It kinda felt like that sort of thing which is why I wondered if I haven't got a good seal somewhere. I may not get a chance to look before the weekend but I'l check ;)

[KEN33Y]

I'm trending towards the vacuum myself Russ worth a look, I think if it were a gasket seal it would be more erratic on as you say normal idling

[ian6]

Have to agree on the vacuum theory, had similar problem on an early petrol jag some 35 years ago, I also suffered occasional difficulty starting and erratic revving, turned out to be a crack on an ageing rubber vacuum pipe.

[Russ68]

Thanks guys, I'll check condition of all and any breathers, later today if possible. I think there are 2, one front and one towards the back.

 

Earlier she was sitting at 1500 when rolling down hill, which was worse than usual.

 

Cheers, Russ

[Raistlin]

Maybe brake servo vacuum take-off as well Russ?

[PD Miller]

Just going off on a bit of a tangent Russ, how do you intend to polish the inlet manifold? I've been thinking for a while of polishing or painting the one on my XJ6 but it's a rough / mottley surface and I think it would be quite a job to polish it.

I think everyone might be right with the vacuum hose theory BTW.

Cheers

Pete

[Russ68]

Hi Pete,

 

When I had the manifold off for the plugs and coil packs, we had a bit of a go at it with a wire brush on an angle grinder. But the steel tines were quite worn and a bit harsh. So I've brought myself a new brush with softer brass tines, which I hope would be just the job. I'll give it a go and post pictures of how I get on. Once the corrosion is taken back, I imagine I'd want to seal it with a polish or laquer it but it should come up quite well I hope.

 

Cheers, Russ