Splutter on warm up

[bugeye555]

Recently my 99 impreza uk turbo start to splutter a few mins after start up , I noticed it seeks to be bang in when the temp guage starts moven up to tempature and only for a few second when the needle starts moving. After it splutters for few seconds then drives perfectly. Also I'll mention drives perfect before temp guage starts moving. Any ideas were to start ?

 

[BazGF8]

When was the last time the spark plugs were changed?

 

[bugeye555]

Plugs and new leads only gone in about 2 months ago and not much driven done since

 

[subiescooby]

could be fuel pressure, MAF sensor, vacuum leak. Wouldn't harm checking leads aren't loose etc.