Mechanical problem

Ralenti problem of Fiat Siena 1.6 8V 1998 from 1000 rpm at 1500 rpm unstable, I changed spark plugs and its cables, butterfly sensor, step by step, air filter, electro-fybec filters and nothing in cold is very unstable until it is corrected only a little, on the highway very well but vessels of vehicles slowly jump a lot. Agrdeso Oriente me. Thank you

Check the distributor.

For the year the Siena has to have e-obd (on board diagnosis), and if you had the opportunity to test it, you would know how to specify a little more the search for the breakdown.

On the other hand, you do not mention that the diagnosis light is turned on, which makes me think that it is a air intake or an error of the flowmeter or MAP sensor (I do not know which of the two it carries) that it is not so fat as to turn the fault light. (but that would be seen with diagnosis).

To see if it is any admission air intake, the test is very easy, the escape covers with a cloth and seal, the air entrance behind the filter with another rag and seal and put pressure on pressure does not exceed 0.5 bar. You spray soap with all the tubes clamps, through the joints and where you form bubbles is where air enters "without permission".

All the best.

Very grateful to Vori and Megabeat_1 the Siena is a monoinjector, if it were the injector with some dirty I imagine that I would also fail in high but does not do it, also the two coils if the guna or both present fault, it reflects it both in high and low, but it is so please guide myself. With respect to the distributor I think it does not have, the Megabeat_1 is more worth it when I can perform the test, I changed the time belt and it was somewhat stretched but nothing remains the same. Thanks for trying to help me