S40 V40: Engine performance down

[Hertsracer]

I have a volvo v40 estate 1.9 turbo diesel, with 98000 2002 52 plate,
the engine runs and starts fine but sometimes it runs very slow whilst im driving as if it runs on 3 cylinders,if i turn off the ignition and then back on i get the power it should get but when i do that the speedo needle goes up and down to zero when i am moving can anybody help on this with thanks phil

[clarkey1984]

If you're doing this while the car is moving then that's the reason for the Speedo, as these have an electronic speedometer as opposed to a mechanical cable one,.you kill the power then you kill the signal so it'll drop to zero, although as for the problem itself, first port of call would be the fuel filter myself.

[Hertsracer]

Originally Posted by clarkey1984

If you're doing this while the car is moving then that's the reason for the Speedo, as these have an electronic speedometer as opposed to a mechanical cable one,.you kill the power then you kill the signal so it'll drop to zero, although as for the problem itself, first port of call would be the fuel filter myself.

No i do not turn the ignition off whilst im moving that would be silly,sorry but i did fail to mention that,i stop the car then switch off then back on then whilst im moving the speedo fluctuates

[Hertsracer]

Originally Posted by Hertsracer

No i do not turn the ignition off whilst im moving that would be silly,sorry but i did fail to mention that,i stop the car then switch off then back on then whilst im moving the speedo fluctuates

ive had the car fully serviced, its like it goes into limp mode when i lose power

[Wagon Sailor]

I've seen that on a Transit van and a Volvo FL10. I think the truck problem turned out to be a sensor in the throttle pedal. I don't know about the van.

How relevant those observations are, I can't say ...

[s40t4trowsdale]

Is it the rev count or speed count

If its the rev count i had it. It turned out to be the icv (idle control valve) which is like £30 from volvo them selfs.

Hope this helps

[Toxicbacon]

First place I'd start is looking for boost leaks, rev the engine up and listen for any hissing or whooshing. Also try unplugging your maf

[aldred309uk]

One cause of power loss which is restored after turning the engine off and on again can be particles in the fuel tank, flakes of rust for example. As the car runs, bits of rubbish can get stuck to the sock on the fuel pick up inside the tank. The longer the car runs the more stuff blocks the fuel pickup causing a lack of sufficient fuel. When the engine is turned off the suction from the fuel pump stops which allows the dirt particles to float away from the sock which allows regular fuel flow again. This may not be your problem but if you find yourself in the area, have a look for flakes and other debris in the fuel tank.

[v40cro]

Could be MAF or EGR, I hade same issues on mine 03 1.9D, best thing is to hook it up to OBD and see if it shows anything, otherwise you might be throwing money away while trying to find issue

[aldred309uk]

Originally Posted by v40cro

Could be MAF or EGR, I hade same issues on mine 03 1.9D, best thing is to hook it up to OBD and see if it shows anything, otherwise you might be throwing money away while trying to find issue

Mine had EGR issues and unplugging the MAF sensor removed all symptoms.