W126 uneven throttle at 1200rpm…

[Scuff]

Hello Guys.
Hope someone can help me with this problem..
I have a W126 500sec coupe 1992. The problem I’m having is, she idles lovely, drives as it should but in traffic as soon as I get to approximately 1000rpm the engine revs up and down like I’m tapping the accelerator causing the car to serge, until I get to around 1300rpm? it clears and back to normal until I slow down and hit the 1000-1300rpm. It’s driving me crazy.

I’ve just replaced the idle throttle position censor, cleaned the small inline filter in main feed to fuel distributor, new spark plugs, new leads and new distributor cap and rotor arm.
Any advice or suggestions would be very much appreciated guys.
Thanks for your time.
Scuff..

 

[rayhennig]

new spark plugs, new leads and new distributor cap and rotor arm.

All of the best quality, I hope. These engines demand the best.

Can you read codes from the circular 9 pin diagnostic socket (pins 2&3)?



RayH

 

[mattkh]

I’ve just replaced the idle throttle position censor,

Did you clean the throttle body.

 

[Doug1234]

Vacuum lines ? , is it mechanical advance retard ?

 

[Scuff]

Hi Guys.
Think I’ve found it I cleaned the in-line filter in the main feed pipe for the fuel distributor and since then it’s been fine. Fingers crossed

Thank you for your reply’s.. they are very much appreciated..

 

[rayhennig]

All of the best quality, I hope. These engines demand the best.

Can you read codes from the circular 9 pin diagnostic socket (pins 2&3)?

View attachment 90154

RayH

Badly worded. I should have said, "Can you read Duty Cycle from the circular 9 pin diagnostic socket (pins 2&3)?".

And read codes from the 8 or 16 pole diagnostic connector.

R

 

[Scuff]

Badly worded. I should have said, "Can you read Duty Cycle from the circular 9 pin diagnostic socket (pins 2&3)?".

And read codes from the 8 or 16 pole diagnostic connector.

R

Thank you so much.
Your advice is very much appreciated. I’ll get on it straight away.
Thanks again.

All the best.
Scuff.

 

[rayhennig]

Some procedures here on Duty Cycle. But you'll have to find the specs for your engine as this only refers to the M104 (mine) and the M119.

The procedures should be much the same.

R