Citroen DS3 engine fault light orange

Engine fault light orange engine comes on coolant blower runs continuously vibrates shaking when at traffic lights or junction sometimes goes into limp mode. The light goes off simetimes & runs ok then comes on again diagnostics done comes up with random misfires ECM fault in memory also ECU not recognised can network intermittent fault paid over £500 pounds for diagnostic & parts but garage unable to fix the problem can anyone help please