hope someone can help.

i have a mk4 astra 1.6 8v 2001.

drives fine no hesitation but sometimes coming up to junctions or roundabout and you press the clutch in to change down the revs just drop to nothing and it cuts out.

also if driving for half hour or so there is sometimes not always a brief smell of like sewer or sh@t. not an eggy smell like a cat.

the temp gauge does not work.. linked?

ok repairs and checks so far. ecu replaced

alternator replaced

coil and plugs replaced

no fault codes stored.

any ideas??