Technical Fiat Panda 141 1000 i.e. (1988) stalls when pressing brake pedal – brake light switch already disconnected

[Fou75]

Hi everyone,


I’m having a strange issue with my 1988 Fiat Panda 141 1000 i.e.: whenever the engine is idling and I press the brake pedal, the engine stalls immediately.


What has already been tested/done:

• Vacuum leak ruled out: brake booster and non-return valve checked → both seem fine.
• Brake light circuit ruled out: I disconnected the brake light switch and tested again → problem persists.
• Idle control valve replaced → no improvement.

Possible causes I’m considering:

• TPS (throttle position sensor): possibly not giving a proper idle signal or has worn tracks.
• MAP sensor / pressure reading: may not be reacting correctly to the sudden vacuum change when braking.
• Grounding / voltage drop issue: poor engine-to-chassis ground could be causing ECU/ignition to cut out.

What I would like advice on:

1. Best way to test and adjust the TPS on this Panda (expected voltages and pinout).
2. How to check the MAP sensor (whether external or ECU-integrated) during idle + brake application.
3. How to measure grounds/voltage drop correctly (test points and acceptable values).
4. Any known weak points in the IAW ECU or wiring on this model that could explain this behavior.

Any tips are welcome — thanks a lot for your help!

 

[portland_bill]

My first thought was air leak to brake booster. Have you disconnected it, and plugged the pipe, to completely eliminate it from the diagnosis?
Only way for engine to know brake pedal is pressed is via brake booster pipe, or brake light switch. If both taken out, and the problem still persists, you need to look at any interaction between brake and accelerator pedals. Time to get under the dash, and see if the pedal brackets or pivots are cracked, or flexing, or any other unwanted interaction.

 

[Fou75]

My first thought was air leak to brake booster. Have you disconnected it, and plugged the pipe, to completely eliminate it from the diagnosis?
Only way for engine to know brake pedal is pressed is via brake booster pipe, or brake light switch. If both taken out, and the problem still persists, you need to look at any interaction between brake and accelerator pedals. Time to get under the dash, and see if the pedal brackets or pivots are cracked, or flexing, or any other unwanted interaction.

Hi, yes we disconnected it, and plugged the pipe.

 

[Fou75]

I took some pictures of the pedals because I don't really see anything strange but maybe I'm overlooking something.

 

[portland_bill]

I took some pictures of the pedals because I don't really see anything strange but maybe I'm overlooking something.

Get your head down there, and get someone to push the brake while you observe the pedal box. Look for any flexing, or any unwanted movements.

(Find someone you can trust not to tread on your head)

 

[Fou75]

My first thought was air leak to brake booster. Have you disconnected it, and plugged the pipe, to completely eliminate it from the diagnosis?
Only way for engine to know brake pedal is pressed is via brake booster pipe, or brake light switch. If both taken out, and the problem still persists, you need to look at any interaction between brake and accelerator pedals. Time to get under the dash, and see if the pedal brackets or pivots are cracked, or flexing, or any other unwanted interaction.

Hi, yes we disconnected it, and plugged the pipe.

 

[puch 4x4]

Hi everyone,


I’m having a strange issue with my 1988 Fiat Panda 141 1000 i.e.: whenever the engine is idling and I press the brake pedal, the engine stalls immediately.


What has already been tested/done:

• Vacuum leak ruled out: brake booster and non-return valve checked → both seem fine.
• Brake light circuit ruled out: I disconnected the brake light switch and tested again → problem persists.
• Idle control valve replaced → no improvement.

Possible causes I’m considering:

• TPS (throttle position sensor): possibly not giving a proper idle signal or has worn tracks.
• MAP sensor / pressure reading: may not be reacting correctly to the sudden vacuum change when braking.
• Grounding / voltage drop issue: poor engine-to-chassis ground could be causing ECU/ignition to cut out.

What I would like advice on:

1. Best way to test and adjust the TPS on this Panda (expected voltages and pinout).
2. How to check the MAP sensor (whether external or ECU-integrated) during idle + brake application.
3. How to measure grounds/voltage drop correctly (test points and acceptable values).
4. Any known weak points in the IAW ECU or wiring on this model that could explain this behavior.

Any tips are welcome — thanks a lot for your help!

Are you losing brake fluid? I was on mine and it was the master cylinder filling up the brake servo strange