Fiat will not perform above idle while in drive bogs down will hardly pull its self?

Answer 1

Engine "Bogs Down" at Throttle Settings Above Idle

I have not worked on Fiats, BUT... I have worked on a few American cars with the same issue, and it always turned out to be that there was some kind of obstruction in the exhaust system.

The first case I had this experience with was on an almost new 1958 Pontiac Super Chief with a V8 engine. In this case it was easy to diagnose the source of the problem, as at any throttle setting above an idle the muffler/tailpipe screeched like a jet engine at takeoff throttle setting!!!!!

Investigation revealed that the internal baffle plates in the muffler had defective spot welds which allowed the plates to move backward in the muffler until the plates were "stacked" up against each other. Since the holes in the plates were staggered, when the plates were stacked they severely restricted exhaust flow at any throttle setting above idle.

Later, as Catalytic Converters were installed for pollution control, it was common with engines running way too rich to buildup carbon inside the very tiny passages of the Catalytic Converter. This would limit the exhaust gas flow such that only the idle combustion exhaust gasses could freely pass through.

At throttle settings above idle, the amount of exhaust gas was too great to rapidly pass through the Catalytic Converter, and as the gas flow was retarded "back pressure" built up causing the engine to bog.

Not being familiar with the Fiat, I don't know if it utilizes a Catalytic Converter, and if it doesn't, another possible cause is some kind of blockage of the exhaust system [like a Potato stuck in the tailpipe, or a crushed exhaust pipe, muffler, or tailpipe. Of course, total obstruction of the exhaust system [like a Potato in the tailpipe] will prevent an engine from running at all.

Since your situation allows idling, but not greater throttle settings, I suspect the the cause is major restriction in your exhaust system.