Wagon r low rpm, knocking, and smell from exhaust

[Engr.Ghulam.Ghous]

I have wagon r 2018 model, recently had head cylinder work due to bad valves. After that car has problem of low rpm i.e 550 to 600. And also rattling sound occassionaly from the engine. And one more issue that i am facing after head cylinder work that is smell coming from exhaust, smell is like burnt fuel. No discharge or smoke from the exhaust pipe
Throttle body serviced, no fault code in the scanner as well, no check light, spark plugs checked after 5000km they are also fine.
Discussed with the mechanic he said he cant do anything as throttle body is autmatically adjusting the RPM.
Kindly advise what to do or advise a mechanic in lahore who is expert in his work.

[pwuser162557941033]

@syncview can help you. His workshop Project 11 is in Johar Town.

[aminjafer5441]

What was bad with the valves? Were they leaking compression? We're the valves oil seals leaking causing oil burning? Was there a bent valve?
Seems like the work done was subpar, or there could be a timing issue when the timing chain was installed. Normal idle rpm of wagon r is usually 690-750 rpm so yes 550 to 600 is low. The rattling sound is a major symptom of loose timing chain. The timing chain tensioner might be malfunctioning causing excessive slack in the chain.

[Engr.Ghulam.Ghous]

Thanks for the reply, actually a mechanic installed an oversized plug in one chamber, due to that one valve cap damaged. So that had to replace the valve.
Does loose timing chain also cause low rpm issue? And what about exhaust smell?

[aminjafer5441]

A loose timing chain might cause low rpm issue but we cannot be certain in this case. Bad exhaust smell could be due to malfunctioning catalytic converter. Was it cleaned by the mechanics with house hold acid?