Sigma Throttle Response

[Pete Underhill]

On my standard factory setup on a Sigma 125, when blipping the throttle on the downchange, instead of the rev increase, I get a 'PSHHT' sound, like a cat sneezing. Then, by the time the engine responds, it's too late and the gear change has been made.

It behaves the same at all temperatures, even after twenty or so laps of Bruntingthorpe.

On normal progressive throttle use, it feels fine.

Can the community offer any thoughts?

[DJ.]

I have a standard Sigma 125, and it blips very quickly on down changes, hot or cold.

Sorry I don't have any real idea what's causing your problem, but it isn't right!

 

I suppose you could look for a manifold leak?

 

Duncan

[Pete Underhill]

It was blipping very nicely until Wednesday.

[revilla]

Throttle position sensor? Check the connector is secure and wires intact. I think the TPS normally gives the ECU a "heads up" on a blip allowing it to repond immediately, before pressure and flow signals stabilise.

[AndyD]

Check the little black rubber tube that plugs into the thing next to the ECU. No idea what it's called so could be what he said . Think it's used on the 125 but disconnected on the 150 (hope so anyway, as my 150 has no pipe plugged into that thing).

[ChrisC]

Its called the map sensor. Its electrical connected on the 150, but the 125 uses it to sense manifold pressure. Its possible you have a split hose between the manifold and the map sensor.

[AndyD]

Exactly

 

[Pete Underhill]

Thanks for the pointers. Once the weather settles down, I'll get out there and take a look.

Cheers