Really annoying problem

[ajl]

Ok this is a bit of a strange problem

I’ve got a 97 318IS with a mileage of just over 204,000miles.

Recently its developed some sort of engine problem (i think).

Basically after about 5 mins of driving I start noticing a slight loss in power under acceleration, the MPG dial instead of reading between 20 and 30 under normal town driving and light acceleration starts going off the scale and shows 1mpg.

This happens on the motorway also, at 60mph the MPG is reading 20 or under (used to sit at 50/45mpg) and if i try and overtake anyone (by only lightly depressing the accelerator) it goes right round to 5mpg or less and there’s definitely a loss in power.

If i come to a standstill, the idle is rough, it seems almost as though the engine is just managing to keep ticking over, but it doesn't cut out or at least it hasn't yet.

I also notice if I'm pulling away normally in 1st and take it up to 3000rpm depress the clutch and change to 2nd it seems to lurch forward or if I’m on the motorway and take my foot off the accelerator it jerks forward, its not smooth like it used to be.

I filled up the fuel tank the other day and before this problem started I would regularly get 400-430 miles from a full tank, I now get 300!

Has anyone experienced these problems before?
Can anyone help me?

Any help would be much appreciated.

[Jeron]

No check engine lights? Any new engine noises?

Some symptoms sound like a vacuum problem, either a leak or maybe the Idle Control Valve is sticking. Other ideas are bad coil, O2 sensor or fuel pressure issue.

[jwfuller]

When was your last tune-up, and when were your O2 sensors last changed?

I want to say O2 sensor, because when you pull off the accellerator, your engine changes output (u know the needle shoots up to 40MPG), and your emissions change alot. If your O2 sensors can't keep up, it is going to mess up your engine management system. That would explain the kick when you let off of the accelerator.

Your O2 sensors are probably hanging in there when you first start up, and then as everything gets hotter (especially the Cats) they quickly lose their functionality.

You need to have your codes read, with that much going on you are bound to have a couple stored.

[whosyadadie01]

yea i to have a similar problem, i just had my o2 sensors replaced but the code hasnt been cleared yet(that mite be my problem). when get on the gas from a light it will feel like i have no power and then at a light it may start vibrating like its about to stall

sorry i cant be much of a help