Dedra 1.6ie acceleration/oscillation

[neil shackleton]

I've been running a '92 1.6ie Dedra until recently and have just acquired another. They both seem to suffer from the same problem. Under hard acceleration from standing there is a very noticeable oscillation as the revs rise and fall leading to a kind of lurching getaway. It's OK if done very carefully but is a pain on something like a hill start, or nipping out into busy traffic. I was thinking it is maybe down to clutch wear, which tends to cause juddering when cold, but have changed one of them and it still occurs. It feels like the clutch is snatching due perhaps to wear in the engine mounts, which are much longer than on the larger engined models. Of course you can't see it from inside the car and I haven't been able to find any play in the engine bay. Has anyone else ever suffered the same problem, found a cause, or affected a cure?

[mikeymikemcmike]

I've had a similar "mode" occur with my Dedra 1.6ie a couple of times. Mine has the Bosch Motronic injection system. The problem can occur if the battery is disconnected or goes flat. What happens is that the ECU "forgets" the calibration for the idle stepper motor but fails to recalibrate it. This causes the behaviour you describe. It makes the drive take-up phase very jerky indeed! There is a section in the owners handbook that covers this.
To solve the problem you have to "reset" the ECU so it will recalibtae the stepper motor which involves disconecting the battery for a while. In my case I tried disconnecting for about 15 minutes as advised in the manual but found this was not long enough. After I disconnected it for about an hour it was fine.

Hope this helps.

Mike

[neil shackleton]

Hi Mike,

That sounds entirely feasible and somewhat easier than changing engine mountings just to see! I've read about re-setting the ecu after the battery has been off or flat and I do think there is some trickery in getting the set-up right again. You're dead right, at low speeds and setting off it's a real pain!

I'll give it a go.

Many thanks, Neil.

[mikeymikemcmike]

It's definitely worth trying and it might take a few goes to get it to recalibrate. If that doesn't work it might be the stepper motor itself. I had this fail on my Dedra and it can also affect starting off from idle. The stepper motor has a switch on the end so it knows it has reached the actual throttle position. To check it's operating correctly look under the bonnet and increase the revs above idle. You should see the stepper motor move outwards until it contacts the throttle again. When you release the throttle it should gradually move backwards to idle again.

[neil shackleton]

I think I know the part, it presses on the end of the throttle cable end stop and sets the idle speed. I think the car I've just got might have been stood in the garage a bit as things like the brake discs weren't at their best initially. You never know what can happen when a car's been stood for a while. I'll take a look at it at the weekend. Fingers crossed.

Thanks again, Neil.