so i have the 2005 1.2 8v punto
and i have noticed when the car temperature is cold and its on idle the revs will drop and bounce back up but as soon as the temp needle is half n half it runs ok but my problem is that my fuel economy is absolutely rubbish now something like 25mpg when before it was around 40mpg.

i did some research and found i should clean the trottle body and idle air control valve. after doing that there is still no difference =s
help plz.

If EML light is on, get a code reader on it.

Failing that, you might try another engine temp sensor/air temp sensor/throttle body/IAC from a scrappy.

Do check that the throttle cable isn't too tight, none of the vacuum hoses are perished and that there are no air leaks on the induction side.

there is no eml and the revs and noise doesnt bother me im worried because my fuel economy is rubbish now. the tb and iac are fine ive checked and ive had a mechanic check them.
might have to check temp sensor and air temp sensor.
this is turnin out expensive lol

You might check that the thermostat is present and working, too.

il just have to pop it dwn to a mechanic and see what they say too if it matches with your analysis then we may hav a fix. well i hope so anyway

Bad fuel consumption is often engine temp sensor or just plain overcooling (thermostat).

Hunting idle is generally too much air (air leak, IAC, throttle cable, etc.).

Might be worthwhile trying swapping the lambdas over, bank 1 for bank 2 -- one might be going sleepy.

A hunting idle could be sticking throttle body as well

Also i found a hunting idle can be made worse with a overloaded alternator
So sat at light with everything on can make the engine stutter as the alternator kick in hard to try and maintain a charge

Ziggy

Well, the idle should be controlled by the ECU. It's fighting with something.