Cold weather idle speed

Right I've been doing a bit more reading and trying to understand lambda sensors, and am I correct in saying the lambda sensors are essentially irrelevant to this as it's only idling high when the engine is cold, so it is running in an open loop condition and shouldn't be relying on them for the fuelling?

Although, as the rear sensor is reading a steady 1.275v until the engine starts to warm up, that suggests it is running incredibly rich so I should be looking more along the lines of fuel pressure/fuel system?

My brain hurts.

Low fuel trim readings are a good sign because it means that the fuelling is actually pretty good. The front sensor will fluctuate once its in closed loop so that's also good. The rear sensor is probably OK, its just a check for the cat. Did the temperature sensor readings look OK?

The front sensor was varying between 0.3-0.9 so that's pretty much bang on what it's supposed to be. The only reason I was concerned about the rear sensor was because the cat section of the exhaust split a few months back and the exhaust was hanging on purely by the sensor wiring for a good 10 miles whilst I crawled home - the cat should obviously be fine as it's brand new, albeit an OEM part not Suzuki. I might as well check the sensor with my multimeter just to make sure.

All of the temperature sensors are reading fine (intake, coolant) and the MAP pressure is 100kPA with the engine off and settles to ~35 at idle so that's reading fine too but I'm going to have another root around in daylight for a vacuum leak. Guess it's just a 'characteristic' of the car and nothing to panic about.

Dougall wrote: my fault code reader is that my throttle only opens to a maximum of 72% even when the engine is hot

I missed this at first. That seems quite low, what fault code reader are you using? the throttle is usually scaled from the idle 'switch' position, that may mean that the TPS is not properly adjusted. Can you read the TPS voltage at idle warmed up?

My code reader is a £20 ebay special - I think it's a Proscan 580. There doesn't appear to be an option on it for reading the TPS voltage as it is very limited, but I've just had a look through the service manual and found this:

Throttle Position, ignition on/engine off
Throttle valve fully closed: 7-18%
Throttle valve fully open: 70-90%

I'm getting somewhere around 13% at fully closed and anything up to 75% at fully open. Still nearer the upper/lower limits though.

I feel like I should be paying for all this advice!

TPS voltage may not be available via OBD2, Suzuki keep a fair few parameters 'reserved' for their dealer tools. Is it a G13BB engine or an M13? TPS doesn't seem to be adjustable on the M13 engine. Have you checked the cable adjustment? Have you got a mat under the throttle pedal?