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leongsoon

Alfa Romeo 156 Selespeed 2002 Intermittent Loss Of Throttle Control

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Hi! A few months ago my car started exhibiting random ABS / VDC / EBD failure. Sometimes this starts progressively, it'll start without errors, but after a few minutes of running, ABS error lights up, and after a few more minutes, VDC failure, and later EBD. Sometimes it'll start with all these errors displayed, might clear off in a few minutes, only to reappear later. Brake pump and rear ABS sensors has been replaced but the problem persists.

 

About 3 weeks ago my 156 started experiencing a sudden but short and violent loss of throttle control when driving, shuddering with acute rev drops and Motor Control System Failure message appearing. This occurs every few minutes or worse, few times a minute.

 

What has been done in chronological order:

1. Charged battery and cleaned the terminals (didn't help)

2. Changed RPM sensor (didn't help)

3. Changed tachometer (didn't help)

4. Ran with MAF disconnected (didn't help)

5. Replaced pedal (drove fine for 80km)

6. Cleaned the 2 connectors on top of throttle body (got some throttle related messages but since gone)

7. Clean big Selespeed connector beside battery

8. Cleaned connectors around shifter and behind glove compartment

 

After replacing the pedal, the car drove fine for about 80km but that didn't last. What I've noticed since:

 

1. Even with the car idle and stationary, the revs will still abruptly drop and probably stall the engine.

2. The rev drop observed isn't as if throttle was suddenly released, rather the tachometer lost readings, the gauge lights and MCSF still work while this happens.

3. I've been monitoring with MES, and every time it shudders, the car loses all readings for pedal angle, throttle angle, rpm etc

4. I've also noticed that sometimes the bulb warning flickers and the Selespeed shifter will fail to respond sometime a few seconds before the car starts jerking again

 

In the early stages of checking and cleaning I've managed to come up with some throttle error messages, and later:

P1763 - Receive CAN messages (Stored)

P0725 - Engine speed signal (Stored)

 

In the past 2 weeks we haven't been able to get any error messages out of it but the shuddering persists. Could this be a wiring or ECU issue? Really at my wit's end trying to figure this problem out. Any pointer is much appreciated!

Edited by leongsoon

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Ok, I had similar symptoms on a clients car sometime ago. It was the firewall junction where the wires for the Throttle pass through into the engine bay.

 

Simply follow the wires from the throttle all the way along to the firewall, cleaning and tightening each connector as you go along.

 

In this case it was the last connector just before the firewall that was the issue. See how you go.

 

Baz

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Hi bazzbazz! We suspected the throttle wires and have checked those, might do it again in case we missed anything the first time around. A peculiar issue is that when the revs drop, we can hear the aircon compressor cutting out as well.

 

We've also switched out the throttle body but the problem persists.

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