Could this be a possible vacuum leak or at very least a concern?

 

Look at the illustration below. You want to ensure a good seal at item #6 and #8

https://parts.jaguarlandroverclassic.../brand/jaguar/

The big body of the duct shouldn't be loose, no. But in and of itself that looseness won't cause an air leak

Cheers
DD

 

Hello, As all the pipework is down stream of the air flow meter, any joint leak is unwanted, unmeasured air. A smoke tester connected to the hose for the fuel pressure regulator and the air flow meter removed and capped off will reveal very quickly if you have a leak any where. You can do the exhaust quickly the same way by plugging up the extra tailpipe and forcing the smoke upstream to reveal any cracked exhaust manifolds.

Thank you

Larry Louton

 

They all do that, to coin a phrase. If there was a vacuum leak your idle would vary as you moved it. It didn’t flicker. The method of attachment leaves a little play if I remember correctly.

 

Hello countyjag, let me see wiggle the exhaust to reveal a cracked exhaust manifold. I own a heavily reworked 1985 Jaguar Sovereign with a 1995 XJR6 engine and a GM E460L transmission behind it.. Gold box fuel and ignition system. The component that is being wiggled is held by a few rubber grommets. It's only a matter of time.

Thank you

Larry Louton

 

The cracked exhaust manifold issue doesn’t involve a loss of vacuum as such. The cracks allow oxygen to be ingested between exhaust pulses which cause the oxygen sensors to believe the mixture is weak, and lead to it being enriched incorrectly. Car can actually run quite sweetly, but fuel economy deteriorates markedly.

 

I've installed headers. Cigar style smoke detector revealed nothing. Rebuilt coil sub-harness. New filter, plugs, coils, fuel regulator, MAF cleaned. Still has rough idle.
May try new O2 sensors next.

 

With new coils they would still be suspect as some based on manufacture can be bad out of stock or shortly after use

Is there a cylinder code that can be followed if coils swapped positions ?

There are some clean - ups before putting in new O2 sensors which appear lately hard to find in stock