Do gas cars emit carbon monoxide?

Go with John

Yes they do,It is much less then gas or diesel but they still produce carbon monoxide,Here is a comparison to some of the other fuels.Hope this answers your question.
LPG produces 33% less CO2 emissions than gas and 45% less CO2 than diesel.
LPG vehicles produce upto 82% less Nitrogen Oxide pollutants than gasl and 99% better than diesel
63% less Carbon Monoxide.
40% less Hydrocarbons than gas and 70% less than diesel.
50% less particulates than gas and 98% less than diesel.
You only have carbon monoxide from a running engine.There are a few other issues associated with storing a leaking LPG vehicle in any structure including suffocation and fire/explosion.
" LPG is heavier than air, unlike natural gas, and thus will flow along floors and tend to settle in low spots, such as basements. There are two main dangers from this. The first is a possible explosion if the mixture of LPG and air is within the explosive limits and there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration. In addition, an odorant is mixed with LPG used for fuel purposes so that leaks can be detected more easily."

What kamakazi said.
Any engine that burns hydrocarbons such as gasoline or LPG or propane is going to produce some CO when it's running. Most is removed (burned to CO2) by the catalytic converter so that committing suicide in the garage is less reliable than it used to be.

Some ferries, tunnels, underground parking garages etc. ban LPG or propane-fuelled vehicles because of the risk of leaks and explosion. If your garage is above-ground with reasonable ventilation like the usual badly-fitting door, and you keep the vehicle maintained, there should be no problem.

carbon monoxide for both but lpg is much lower

All fuels obtained from Crude are Hydrocarbons (C,H compounds) and therefore emit oxides of Carbon on combustion. LPG has no odour and for this purpose Ethyl mercaptan is added to it during production and this gives it a pungent smell when in contact with air, meaning, you would be able to detect a smell in case there is a leak.

Burning LPG car gas does release carbon monoxide, along with carbon dioxide.

I'm going to say that they can, because when LPG evaporates it turns into the gas that is used often to heat homes, and I know that gas can create carbon monoxide if there is something wrong with the chimney or the furnace.