My Renault Clio 2 1.4 16V , 2007 model engine has the following problems.
(1) At cold start the the engine shoots up to 1200, when I step on the gas to rev up to 2000 and release pedal, the RPM keeps increasing up from 2500 to 3000 even if my foot is not on the gas. This does not happen when the engine is warm. (2) When warm RPM will drop to 600 rpm and is unstable. (3) Power or acceleration is weak. (4) I can hear a hissing sound while the engine is running and the mechanic tells me it s normal. I am sure I do not have that sound before they replaced my valves, cylinder head when my belt broke while running at 120kph. (5) there is no check engine error. (6) The shop replaced spark plugs, O2 sensors are ok, replaced the intake manifold assembly because they said there was a valve between the oil and air (diagphragm type) that s broken validated after the smoke test.
The acceleration is better now after (6) was done, but still (1), (2) and (4) still occur as of this morning. They said there is an ignition cable that is high resistance, they ordered a part and will replace it tomorrow.
I am now lost of what is really the problem. Is that hissing sound normal? Please advise what should I do, I have a feeling of being scammed, this repairing is now about 4 weeks, still not fixed.