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Discussion Starter · #1 ·
I seem to have a slight issue with my phase 1 twinspark. If I suddenly floor the throttle (either in gear or when changing gear) then I get a feeling like the engine torque output oscillates for a couple of seconds before settling down and consistently pulling hard. If I'm slightly more careful then I don't think I can fault the performance and will eagerly rev all the way to the limiter in 2nd and 3rd.
The resonator is present (otherwise I could believe this was an intake resonance playing with the MAF if it had been removed).

Anyone with any ideas?
- MAF?
- lamda sensor?
- blocked/dirty air filter?
- leak in air feed?
- resonator actually filled with expanding foam?
- can an engine mount cause a wobble in output?

The only other thing is that sometimes it might sit at very low revs for the first second or two after starting before settling to its normal idle speed.
 

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O2 arena...

How many miles has the O2 sensor done?

If 60k + then it may well be dying...

And what state's your battery in? It should have c. 12.7 V minimum without the engine running...

I seem to have a slight issue with my phase 1 twinspark. If I suddenly floor the throttle (either in gear or when changing gear) then I get a feeling like the engine torque output oscillates for a couple of seconds before settling down and consistently pulling hard. If I'm slightly more careful then I don't think I can fault the performance and will eagerly rev all the way to the limiter in 2nd and 3rd.
The resonator is present (otherwise I could believe this was an intake resonance playing with the MAF if it had been removed).

Anyone with any ideas?
- MAF?
- lamda sensor?
- blocked/dirty air filter?
- leak in air feed?
- resonator actually filled with expanding foam?
- can an engine mount cause a wobble in output?

The only other thing is that sometimes it might sit at very low revs for the first second or two after starting before settling to its normal idle speed.
 

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Discussion Starter · #3 ·
Maybe I need to get Alfa diags and a laptop out this weekend.
I'll check the battery as well - is the theory here that the alternator load is changing how the engine is loaded or that the sensors are giving unstable readings due to low voltage?
 

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Discussion Starter · #4 ·
Ok what about the throttle potentiometer -- look at this description from the workshop manual:-

THROTTLE POTENTIOMETER
This is a potentiometer the mobile part of which is
controlled directly by the throttle valve shaft.
The potentiometer signals the control unit instantaneously
when there is the need for "full power", anticipating
the signal from the air-flow meter which records
a considerable increase of the flow of air, thereby
obtaining a more immediate response.
The potentiometer automatically detects the throttle
closed position through a "self-adapting" function.
This eliminates the need for potentiometer adjustment
operations and makes it possible to follow in time any
wear occurring on the throttle closing position.

I've only had a bad potentionmeter previously on a Fiat Punto that would intermittently rev wildly at idle (but with no torque to go with it, so if it happened when in gear you would only notice when changing gears).

Anyway might be worth a go, it's possible that if it isn't notifying the ECU then I only get the drive when the airflow sensor sees the change in throttle position and this isn't tuned to make the ECU increase fuel demand in one big lump, and gives the oscillation.

Anyone ever changed one?
 

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Discussion Starter · #5 ·
Well I've been out to the car and given the cable a wiggle, no difference.

Looks like Eper had this down as 7637025, I've seen cross references come up as a bosch 0280122001.
 
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