I have a 2002 2.5 petrol. Aits got just over 100,000 km on it with a full service history.

It starts and runs fine, but with an occasional rough idle until warm. After driving for about 45 minutes to an hour, or shorter in heavy traffic, the car loses all power and will not drive up any hill or accelerate. It starts revs, and idles perfectly. Just completely gutless. Letting it cool down fixes the issue.

It does not happen when the car reaches operating temperature, but seems to be once the engine bay gets nice and hot. The check engine light does not come on and the coolant temperature is also OK. I ran a code reader and got the full set of cylinder misfires (p300, p310, p302 etc) plus p1646 and p1647. No other codes appear.

I would have thought a single sensor failing when hot would be more likely than both O2 sensors. I thought the MAF would be a likely culprit, but no codes are appearing for that. Can you simply disconnect the MAF on a 2.5 to confirm and still have the engine work?

Any other ideas? I really don't want to have to put it into a jag specialist with a problem that only appears after driving it for an hour.

Cheers,

Darin

 

O2 sensors wear so start by changing the easiest one then if trouble persists the other one as well. Don't use cheap non-OE-type ones or you just get to do the job again and again.

 

If you are getting those codes when you scan it you most definitely would get a check engine light come on. Do you know if those could be old stored codes or are they recent? You might want to delete the codes and see what comes up. At least you know what you are dealing with.

Do you ever get a flashing light showing on the dash when this happens?

Have you checked the intake manifold gaskets or know if they have ever been changed?

What kind of fuel do you run in it? Have you ever changed the fuel filter?

How long have yo had this issue? Did it just pop up recently or have you had it for awhile? When you first started having the issue was there any recent work done?

 

A failing fuel pump is a definite possibility.

 

Sorry for the delay responding i was away for work.

It just started happpening, not after any work. I use 95 octane and am using the sa,e petrol as before any issues. I definitley do not have an engine light on but it works.

I idled it until warm then drove it around with the obd dongle connected and app running. When the fault finally reappeared it turns out the fuel pressure dies off when i try and accelerate, but it idles fine. Ie at idle the fuel pressuree reads 380, but drops below 100 as the engine sies under acceleration. There are no other codes or obvious data issues.

I'll try the filter then the fuel pump (as per sov211 also) I think the 1646 and 1647 are not really causing this problem.

Thanks for your help and i'll come back either way to confirm.