Engine miss & Vibration and Speedometer not working when the engine gets heated.

Dear Sir,

My Name is Sajith and I'm from Sri Lanka. I bought Kia Cerato 2007 model car few months ago. I do have two problems with it where most of the engineers could not solve.

1. Engine miss & Vibration,
2. Speedometer not working when the engine gets heated.

For the Engine miss, changed the ignition plugs and done the engine tuneup. It was ok for two days and it started the miss again. Then I changed the Extension wire ignition coil and one ignition coil which was not firing. But the problem did not solved.
With this engine miss the petrol consumption has reducedto 4-5 kms per/litre even without A/c. Earliar it worked 10 kms per/litre with A/c. What could be the problem for this engine miss.

And for the speedometer it stops working after driving about 7-8 Kms. And if you stop the car for two hours and start driving again it stops working in another 4-5Kms. I have showed these problems to the Kia Engineers but did not get proper solution.

Much Appriciate if you could advice me on these.

Rgds,

Sajith