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[MutantCav]

Ok guys, picked up my nice cheap 1999 Omega 2.5 v6 Estate today, everything is as it should be except for one thing...the way the engine runs...ok, the symptoms are as follows as far as I can see...

engine idles ok although exhaust sounds slightly rumbly from the rear but its new...there is a slight hiss sound from near the passenger footwell but overall the engine idles pretty nice...oh and there is a slight and strange noise coming from the plenum which I dont think I have heard on any of my previous cars before.

Problem occurs when you press the accelerator, even gently it sounds like its running rough suddenly...but accelerates pretty well (better at speed, not so well at pull away but then I did have a lot of extra weight so hard to judge) and the hiss goes away. Its just done 180 miles towing another car so and the engine temp was fine, 93-95 degrees, returned 20mpg average despite a ton of extra car on the back and pulled at 60 sounding on the whole pretty good so overall seeming like its nothing major.

My thoughts are its EGR valve or maybe a slight air leak etc, any ideas?

P.S. Havent checked for oil in the plugs yet as its dark!

[JamesV6CDX]

I would be methodical

A) Check for obvious air leaks
B) Check for DTCs
C) Check for oil in plug wells and condition of plugs/leads

What's the service history?

[MutantCav]

What are DTC's?? Has full service history but engine was changed 40k ago (apparently) and its maybe slightly questionable...

[JamesV6CDX]

Sorry,

Fault codes.

When was the cambelt kit last done mate?

[MutantCav]

Havent had a chance to check for fault codes...been a long day lol will do tomorrow...but assuming its true, brand new engine 40k ago so belt would have been done then.

[markey mark]

at 40k its due again chris every 40k or 4 years !!!

[MutantCav]

Indeed, and there is a cambelt party coming up which I may well attend But I wouldnt have thought this was anything to do with the issues I'm experiencing?

[JamesV6CDX]

Indeed, and there is a cambelt party coming up which I may well attend But I wouldnt have thought this was anything to do with the issues I'm experiencing?

It would be if the valve timing is out by a few degrees

Although it's not the first place I'd look.

Never rule anything out, there are lots of unknowns on a 2nd hand car...

[MutantCav]

I'm wondering what the hissing noise is, its not overly loud, just like a speaker hiss if you didnt have a channel on the radio...but only the passenger side footwell and only when the accelerator isnt pressed...but then the grumbling from the engine only happens when the accelerator is pressed...not sure if an air leak would be audible all the time?? Would no doubt cause a rough engine on acceleration though? Idles at 500rpm though no problem

Incidentally where should the estate exhaust end, before the back bumper or under it and out the back?

[PaulyQ]

Hiss will most likely be the Secondary Air Injector and is quite normal

[cem_devecioglu]

May be good idea to check air leak around plenum..

[TheBoy]

Hiss from passenger footwell suggests the vacuum pipe come off.

[MutantCav]

Where is the vaccuum pipe? and would this potentially cause poor running on acceleration??

[TheBoy]

Where is the vaccuum pipe? and would this potentially cause poor running on acceleration??

There are various actuators for heating system behind the glovebox.

Vac leaks, like air leaks, can cause poor idling, not sure about your symptoms though  :-/

[MutantCav]

So whip out glovebox and see if you can see where hiss is coming from?? Well that could be one issue down even if its not related to the engine problems