Futura a bit lethargic low down.

[blacklabel]

Evening all

Looking for a wee bit of advice here before I go getting a full diagnostic done on my 98AU Futura.She's done 255,600km and still goes great.Starts first time every time!I recently gave her a full service with new filters,oil and plugs.Went for a trip up north and she went sweet as-mid range and top end power is awesome.Even at 120km per hour I could kick down to overtake and she takes off!
But what I have noticed lately(before service also),is a bit of lethargic performance in the low rev range-your general around town driving.
At service I went to a slightly heavier grade oil,but I doubt this is the problem??
Plugs and leads are fine,compression is spot on,no excess fuel comsumption or weird flat spots or the like.
So,after reading other similar posts and replies should I be looking at the O2 sensor and cat first? I wouldn't know the O2 sensor if I fell over it,and don't know what I should be looking for on the cat.It certainly is not rusted or damaged on the outside,but thats not what counts is it?Exhaust note sounds pretty normal.
Any advice appreciated.

[sly]

The O2 sensor is screwed into the exhaust between the manifold and the cat. It has 4 wires going to it. You can't really check it, although you may be able to notice if your exhaust smells rich when hot idling. This may indicate the O2 sensor, but only if your cat is all good.

If your cat has collapsed it will have chunks of what looks like charcoal rattling around inside it. It might rattle if you give the cat a bump with your hand (while it's cold...) or if it's flanged both sides you could unbolt it and look inside. If there are no loose chunks it's probably OK.

You mentioned heavier oil. I found a noticeable decrease in low-rpm responsiveness when I put 15W/40 in instead of the recommended 5W/30. It got better when I switched back to 5W/30.

How's your air filter BTW?

[Bushbasher]

When was the last time you had the trans serviced?

[b2tf]

Originally Posted by sly

The O2 sensor is screwed into the exhaust between the manifold and the cat. It has 4 wires going to it. You can't really check it, although you may be able to notice if your exhaust smells rich when hot idling. This may indicate the O2 sensor, but only if your cat is all good.

If your cat has collapsed it will have chunks of what looks like charcoal rattling around inside it. It might rattle if you give the cat a bump with your hand (while it's cold...) or if it's flanged both sides you could unbolt it and look inside. If there are no loose chunks it's probably OK.

You mentioned heavier oil. I found a noticeable decrease in low-rpm responsiveness when I put 15W/40 in instead of the recommended 5W/30. It got better when I switched back to 5W/30.

How's your air filter BTW?

Oil and air filter would be the first things Id look at.

[curtleyw]

+1 for the oil.
I used 15W/40 and performance was extremely sluggish under 2500 rpm, switched to 10w/50 much better but still noticeably sluggish. So next change I will be trying 5w/30.

[blacklabel]

Thanks guys- trans service was only 2 months ago.Air and oil filters are new,as are plugs and recent renewal of leads.
Thanks for the heads up on the O2 sensor and cat sly, I may have a more thorough inspection over weekend.
From the other replies in regards to sluggishness with heavier grade oil-maybe that is the cultprit after all.I might drain her and go back to 5w/30.