sometimes have power somtimes don't help?

[jasonpeace91]

Hello all,

First of my Berlingo is an 1.6 petrol 
when i brought it  knew it had a slight missfire i replaced the coil and the lambda sensors and that seemed to clear it up
but every once in a while it starts loosing power (feels like ive let off the throttle) and doing 60mph is a real struggle, also
idling is very poor stalls often, but after its sat a while it fires up fine and drives fine for about a week then does it again

any ideas what it might be? 

many thanks
jason

[3rensho]

Hello Jason and welcome. First thing I'd do is to get a code reader on it to see what error messages are being written. Could save a lot of trial and error.

[jasonpeace91]

thank you for the quick reply 

sorry forgot to put i had it code read after it happened the first time by the RAC as i thought it could have been a serious problem but when the rac turned up the only error that showed up was system too rich although by the time the rac turned up it was behaving again

[Solent]

Basics first, is it due a full service, spark plugs etc.