2.8 running rough

[Muther Trucker]

hi, can anyone shed any light on this for me:

2.8 lwb, 1996, auto.

starts fine, first touch. drives fine when moving, changes up and down gears fine.

when ticking over in neutral it is around 760 rpm, if you hold the footbrake and select D the revs stay at 760, and as you release the brake the car sets off rather than holding or creeping, this actually drives off.

Then when you come to a stop still in D, say at a junction, the revs become erratic, dropping + to about 400 + back upto 760 and sounds very lumpy as though its going to cut out or stall, also does it if you are reversing, you have to press the brake to reverse with control, and the revs start jumping as you do it.

I thought the 2.5 auto i used to have used to drop the revs slightly when you selected drive from N, down from &50 to around 600? does that sound right?

any ideas where to start??

cheers, mik

[dragon]

mick have you checked all your fluids etc and is egr valve clean and intercooled clean ....
not realy sure at this point as there seems to be a bit of a mix of faults but i would be tempted to give it a bit of a clean up and check trans fluid etc then clean all the connections up on all the sensors on top of the engine one by one and give it a bit of a run each time just incase one of them is on its way out it may help in locating the fault

[Muther Trucker]

the atf seems ok, the egr has been disconnected, not looked in the intercooler yet.

the guy i got it off said he had had the pump seals done, wondering if thats been done right, or put back together right?

[Muther Trucker]

if anyones got some photos of the locations of the sensors + the pipework to the egr and the other 2 things on top it would be a great help

[dragon]

hmmmm mick give me a ring i have a few ideas what it could be 07874316179

[dragon]

thinking gearbox to engine speed sensor or possibly faulty rev counter / speedo cos that will make the gearchange erratic and makes gearbox change up and down and surge and also revs will be all over the place

[Muther Trucker]

had another closer look at the atf, after going through all the gears there still seems to be too much of it, its showing well above the hot max marks, upto the first bend in the stick. the dipstick above the line of the oil comes out with dirt on it, and the oil is darker and smellier than new oil out of a bottle, so going to have to change that first job i think...


also yesterday i took the intercooler off, leaving all the vac pipes in place, and ran it while wiggling all the electrical connections above and aroung the pump aswell as those between the rear intercooler brackets, it stopped juddering and ran fine, put it all back together, fine. went for a run, fine. pulled up at a roundabout and it started again... now just as bad as ever.

also ran dog rough this morning from a cold start...

[dragon]

may need to clean the sensors real good with electrical cleaner or some wet n dry and wd40
but sounds like just summet and nowt has worked loose causing the faults .
clean every thing you can bit by bit and test after each bit you try ,,,that way you will know where to look if it re occures

[Muther Trucker]

changed the atf today, no imporvement.

wd40`d a lot of connectors yesterday, no improvement.

next job remove the senros off the back ns of the gearbox and check that + the worm drive, not holding out much hope here though, cos the speedo needle never jumps about, its just the revs and the rev counter that fluctuate, and only when stood with foot on brake and in D,2,L or R.

[Trojan]

I had this happen on my 2.8 last year and it turned out the fast idle screw adjuster had come off.

You'll find it on the throttle linkage, just below where you would pull it to rev the engine if you were doing so from under the bonnet.

On a 96 auto, you have a fully electronic fuel pump and if the fast idle adjuster is missing, the ecu tries to compensate by adjusting the fuel flow within the Area Network and that leads to erratic rpm. I am not saying that is the problem, but that was the problem for me. If the fast idle adjuster is present, I wouldn't have thought the ECU would allow rpm to drop to 400.

The fast idle adjuster is a 6M bolt if I remember and needs a locking nut to stop it being rattled out of its location and making a minor issue seem like a major problem.