FEV - Fuel Enrichment Valve. adds a bit of gas to richen the mix to aid in cold starts. Its' supossed to shut off after the motor has warmed but it's a electrical thing so it's not dependable and prone to cause problem at times. If the fev was at fault the motor should still fire up but run crappy due to a rich mixture. I would suggest checking valve lash. The valve setting tend to tighten up after a while and cause the problem you describe
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