Had the EGR changed on my 2.2d X Type Jaguar and now the fuel economy according to the trip computer is 35/39 instead of 42/44 mpg. If I disconnect the battery will that cause the ECU to reset and establish new settings for the new EGR?

My Buick Le saber gets 25 to 30 on the hi way depending how far I drive but around town I get 12 to 18. The reason is short trips the engine does not warm up so your choke automatically kicks in and does not shut down till the engine is up to temperature. Also Short runs means a lot of changing gears so the engine is reving and slowing down for stop lights etc. To get good milage the engine has to maintane a constant even speed.

To put it as simple as I can --the faster you go the more fuel you use-- Not rocket science really.-- At the recommended speed the vehicle is in the optimal torque range and is returning the best economy for that speed . any thing over and it takes a big nose dive.. At the recommended speed you have maximum control of the vehicle and it will last the longest time . Now you have to improve the economy by paying attention to the following items
Tyre width , size pressure is critical to economy
Loads being carried at speed is critical to economy
Add-ons such as load racks add to fuel usage so take them off.
Fast take offs at lights uses fuel. If you let the engine bog down instead of changing gears will use fuel.
Not using the cruise control uses more fuel as every time you alter the accelerator pedal position that is extra fuel being used.
Using E fuel mixes will lower economy. So economy is a matter of your driving habits and not of the make of vehicle.
If you want better economy at the speed syou travel at then visit a speed shop and have the CPU re-chipped for more power at the higher rpm's but be aware that it may void your warranty on the vehicle.

Yes hook up to a code reader pull out trouble codes and follow steps in trouble shooting tree to repair problem. If you dont have a code reader or scan tool go to a parts store (Auto Zone,Pep boys) they will hook up and read codes out. They will try to steer you in the direction to go or just write down the codes and Google them in your computer and you will get list after list of how to fix the problem.

Lead foot, tire pressures, stop /go driving. AC/poor compression, Trunk full of sandbags, transmission slipping, Wheel bearing friction, Brake shoe always on, etc.

If you want fuel economy then dump this beast and buy a nice peugeot or citreon picasso diesel manual then you will get around 30 mpg around town and anything up to 70 mpg on a run ,try paying our fuel prices and this nice typical american petrol gas burner would be delegated to the classic car sunday drive out like my jag with its 4lt engine i can only afford to take it out once a month or so on a jaguar club run around ,other than that its my ford diesel manual escort with its 0 to 60 in 15 minutes but it only uses one tank of fuel a month.

The two buttons that control the trip options are on the dash adjacent to the hazard warning button. Press the TRIP button untill it shows a small A or B in the top left (say average mpg) then press the upper part of the toggle switch marked RESET/CLEAR and hold it for about four seconds, this will display A or " B resetting" depending on which trip you are currently in, then everything on that trip is reset to zero (mileage/mpg/ave.speed etc). I use A for the full tank recording and B for individual journeys that I wish to record.

Instead of an EGR valve you have variable timing on your cam shaft. I would talk to a Toyota dealer. There may be a service bulletin about replacing the ECM (control box) for the variable cam timing which would effect the fuel economy of your vehicle the same way a stuck or plugged EGR valve would.

if there is also black smoke coming out the exhaust - and the problem is intermittent - then it's the EGR valve - it sticks open - will need replacing.... Happened to mine this morning and this is what the Jaguar Assistance guy said. Mine is a 2006 2 litre X-type.

There is a tech bulliten for ecu reprogramme that Jaguar use regarding the hesitation. Black smoke is normally due to a clogged up egr valve. Can be cleaned out easily

if it is diesel i had the same problem plus poor mpg. it turned out to be the rubber pipe from the egr valve to the intercooler that was split cost at jag dealer £73.27 hope this helps. boovie