fast tick over from cold

hi , my 1999 jimny has started a strange fault , when starting from cold it tickes over very lumpy at less than 500 rpm , within about a minute the tick over rises to about 1500rpm and stayes there it will then occasionally co ough and the rpm drops a bit but then returns to 1500 rpm , and stays there no matter how hot the engine gets , the temperature gauge goes to normal and the car drives very well , occasionally if you stop the engine and restart it the tick over goes to normal , there appears to be no other problems and it drives very well , any ideas ?

new fuel filter needed
fault starts like cold start switch knackered

hi thanks for that , pardon my ignorance were abouts do i find the fuel filter and cold start switch ?

The fuel filter is attached to the fuel pump inside the fuel tank and a real pain to change. I'd leave that 'till you have exhausted all other possibilities. Most likely, if it pulls well, and will do 80mph, the filter isn't blocked.

There is an idle speed control valve attached to the throttle body that could have a loose connection, or be blocked with black gunge: try cleaning the throttle body.

There are various rubber pipes to do with emission control, one sucks vapour from the cylinder head through a grey poppet valve. These can fill up with gunge and even freeze in cold weather.

There is also a rubber pipe from the inlet manifold to the vacuum valves for the hubs, this can split or break off and play havoc with the idle speed.

I don't know if this will help you but I had problems with my idle, I changing out the PCV valve and cured it, its a 2 minute job.
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