need help

[ba.wells@hotmail.co.uk]

its a long story so I will make it short iv got the simble on the dash the box with a heart beat in it anyway ive changed the hd leeds,plugs,throttle peddle and throttle body but it still comes on some times it comes on after about 20 mins drive and the other times its on from cold start and if u turn the key on and off(a few times)it goes off ive just got it back from Renault and they said it could be the wiring loom or the throttle body or both but they want 750 to fit the loom and 400+ for the throttle body
I don’t much money so I wanted to know if there is a way around it or any idea what I can do next I just want to fix it then sell it soon as poss.
Please help!!!!!!!!!!!!!!!!!!!!! :S