W124 E280 4-Spd Auto Est (‘95)

[JensH]

Not posted for a while, since I’ve had around 25-30k trouble-free miles (apart from self-inflicted odometer jam last Summer, which was an easy fix). Nearing 180k now.

BUT...

A few weeks ago I had my local garage fit a new cat, an after-market one (recommended). Since then I’ve had both cold start trouble and intermittent shudder / variable revs at idle.

Generally, the car needs a foot down start and 1-2 mins warm-up, to avoid a stall when drive is engaged. Start is fine after 2-3 mins drive, but idle is juddery sometimes and, very occasionally, there is a hint of drag in acceleration. Motorway and long-distance driving is fine, though.

Since there is an obvious follow-on from the new cat, I wonder if the timing should have been adjusted? Or if the cleaner exhaust has side effects?

There is no cold start valve on the M104 E280, because it has VVT.

Any suggestions?

 

[rayhennig]

Not posted for a while, since I’ve had around 25-30k trouble-free miles (apart from self-inflicted odometer jam last Summer, which was an easy fix). Nearing 180k now.

BUT...

A few weeks ago I had my local garage fit a new cat, an after-market one (recommended). Since then I’ve had both cold start trouble and intermittent shudder / variable revs at idle.

Generally, the car needs a foot down start and 1-2 mins warm-up, to avoid a stall when drive is engaged. Start is fine after 2-3 mins drive, but idle is juddery sometimes and, very occasionally, there is a hint of drag in acceleration. Motorway and long-distance driving is fine, though.

Since there is an obvious follow-on from the new cat, I wonder if the timing should have been adjusted? Or if the cleaner exhaust has side effects?

There is no cold start valve on the M104 E280, because it has VVT.

Any suggestions?

Your car is more recent than mine with different fuel/ignition management so wait for the brainy boys before any drastic moves. Also, cold start difficulties might suggest I've got it wrong.

But, if they've been playing around in the exhaust, is it possible that they've disconnected/dislodged/damaged the O2 sensor or its connections? Judging by your symptoms, that would be my first port of call.

RayH

 

[JensH]

Cheers, Ray

 

[LostKiwi]

That would also be my first thought. As yours doesn't have full lambda feedback (post 94 I believe) with a second O2 sensor after the cat the presence or absence of a cat would be undetected by the car and the car would have no idea what cat was fitted.
Not 100% sure but I believe the timing is electronically controlled so nothing much to be done there (you may have a plug on the side of the ECU box which can be rotated for different ECU timing parameters but I'd leave it alone if it was running OK previously.