I have a mercedes MB140 2.3ltr petrol van. running fine until 2 weeks ago. Just driving along normally and I lost power to accelerate. when stopping it was idling rough. But by turning the ignition on and off power came back. Was told it was the stepper motor in the throttle body... But have changed that twice and still no good. Just seems to happen at anytime, dosent matter if theres load or no load? Can anyone suggest an answer?

SOURCE: rough idle / varying oil pressure when accelerating

Ok not to keen on newer vehicles actually prefer the carburated ones, but oil pressure is supposed increase on your gauge when accelerating. If it wasn't going up before and just staying at 40 the needle might have been stuck. But idle should be 40 lbs and when you work the moter (reving or driving down the road) the guage should show an increase for every 1000 rpm above idle. Second if you can get a hand held scanner (bought mine off ebay for $30) check for any codes in your computer you will probably find that you either have a bank running wrong or some other sensor that needs to be changed. I'd go with getting my own scanner it saves alot of money and time, garages make their money here.

SOURCE: ENGINE VIBRATION AT IDLE BUT OK WHILE DRIVING.

Could be any one, or more, of the following -

Plugged injector
Bad plug wire
Fouled plug
Crossed plug wires (hard to tell sometimes on V-8s that run smooth anyway)
Vacuum leak
Leaky EGR valve
Shifted timing sensor

Scan engine for codes and proceed from there.

There is a product called RXP (available here in Texas) that will clean up an engine and gas. Its pretty awesome stuff, and this coming from a person who doesn't really believe in additives.

SOURCE: I have a 2004 Chevy Malibu. Bogs down and stalls

make sure you have ngk or ac delco iridium plugs installed. Also common problem on the 2.2L ecotec is the cat plugging. Easy check is to remove the front o2 sensor (very easy 22mm wrench) and start the car and rev it. If it revs freely now and does not bog the cat is plugged. They are covered fed. emissions warranty 8yr 80k, all gm dealers stock the cats for the 2.2 ecotec.

SOURCE: 93 Nissan Altima idles rough and has no power.

check exhaust back pressure . can have no more than 2 to3 inch pounds off pressure. may also want to check timing marks.

SOURCE: 1999 Toyota Camry V6 idles rough and stalls after

yes it could be a fuel related problem, when was your last tune up, it could also be a spark issue, old or corroted spark plugs will sometimes not put out the correct amount of heat to ignite the gas correctly till it runs for a while, if the check engine light isnt lit, it will almost have to be something simular to this