Very rough idle when cold

Hi Guys,
On the weekend I was adjusting the throttle gate linkage on my D-Jet 350SL and after adjusting one of the input rods to the correct dimension, went to start the engine. It starts but now runs VERY rough when starting from cold (I say 'runs rough' meaning at all engine speeds - this isn't just an idle problem). So rough in fact that the engine will die if you don't keep your foot on the accelerator and looks to be shaking itself off its mounts. I am extremely doubtful that adjusting this mechanical linkage is the cause of the rough running but mention it just on the off chance it has something to do with it.
When the engine gets up to temp. it runs fine and smooth with strong acceleration. Once when trouble shooting yesterday it suddenly came right while still cold, ran fine for a few moments then went back to it's rough running. This led me to think it could be a fault in the wiring harness but no amount of twisting/moving the harness had an effect.
Once the engine is up to temp. it is almost like operating a switch and the engine comes right which makes me think ECU isn't adjusting fuel for cold running and also confirms temp. sensor must be operating.

All vacuum lines checked satis.
Air Cont. Valve is operating fine
Fuel pressure good (2 bar, increasing the pressure to 2.7 makes no difference)

Any suggestions appreciated.
Neville Andrews

Hi Andrew,

it sound slike you have either a vauum line or a wiring harness problem. Hard to say from here.

Hi Volker,
Thanks for the reply.
I replaced all vacuum hoses and inlet manifold gaskets when I replaced the MAP sensor which you sent me in January so don't think it is a 'bad air' - vacuum problem.
Wiring harness is a possibility. As it seems to be related to engine temp. is there a temp. sensor which the ECU only looks at for cold running?
Alternatively do you have a flow chart showing ECU control function?
Also do you know what the throttle gate linkage (only on early R107's) input from the transmission is for?
Thanks.
Neville

Hi Neville,

I don't know much about gear boxes. But this link from gas linkage to gear box is for contol pressure. It affects the rpm points there the gears are shifted. What you can do: Remove the linkage and see whether your problem will be gone.

The mystery is solved!
Following research and testing all temp. sensors were found to be serviceable. Focused now turned to the wiring harness - one of Volker's suggestions - and while I couldn't fault the harness itself it turned out the connector to the Trigger points was not fitted correctly. It appears I dislodged it while re-routing the HT leads so that I could fit the rubber cover over the distributor cap.
So after a clean with contact cleaner and reconnection the engine is back to normal.
Thanks for your help Volker.
Neville

Hi Neville,

thanks for the feedback and enjoy riding your car down under in New Zealand.