Low top speed problem

[fenixQ]

I recently bought a 2000 alfa 156 with 59000 miles on it. I changed the timing belt, spark plugs and did a full service at a local garage but didn't change the variator although the engine was making diesel engine like noise. The problem is that the top speed it would do is only around 130 km/h. Sometimes when I drive it over 80 km/h I feel like the car is going to slip off the road. I took it to an alfa service center and after doing the diagnostics they said the maf is broken and they couldn't find anything else wrong. I disconnected the maf cable and tested it and the top speed I was able to achieve was only around 110/120 km/h. I had a used maf fitted to it from a 99 model 156, still no change. I also had the wheel balancing done on all the 4 tyres. Can somebody help with troubleshooting the problem ? Thanks in advance..

[Rockhopper]

Did you use cam locks and a DTI when you did the belt? Maybe the cam timing is out.

[Smaky]

Whilst it's running feel the inlet manifold, if it gets hot then you've got bent valve from bad timing, Also replace the MAF with a NEW Bosch unit (NOTHING ELSE), and clear the fault codes and reset the ECU. It should then sort its life out.

[fenixQ]

Thanks for your replies. I am not sure how the garage people changed the belt. They told me that a special tool was needed to change the belt on alfa's and I had to wait till they ordered and got the tool before I could get the belt changed. Can you please tell me where the inlet manifold is located ? If the cam timing is out and the valve is bent, would it show on the computer when a diagnostics is done ?