The body which decides whether council services are up to standard should "raise its own game significantly", a report by MPs suggests.
The Local Government Ombudsman takes too long to deal with some cases and has to prove its value to the taxpayer, the Local Government Committee says.
Otherwise it will "undermine its own role and credibility", it adds.
The LGO, which is funded by the government but is an independent body, handled 21,840 complaints in 2010/11.
The committee's chairman, Labour MP Clive Betts, said: "LGO has been taking far too long to determine some cases. One of the ombudsmen conceded that the delay in determining some cases was itself likely to amount to maladministration.
"This must raise questions about the LGO's authority and credibility. The organisation needs to apply strict deadlines to all the cases that it handles."
The committee found the LGO needed to provide a "clear methodology to measure levels of customer satisfaction and publish the results".
It added: "It must also put in place arrangements to ensure there is an annual evaluation of its own activities and decision-making by an independent external reviewer, to ensure the LGO is itself fair, effective, open, transparent and accountable."
This reviewer should be appointed by the end of this year and report for the first time no later than Easter 2013, it added.
The cross-party committee said: "An organisation whose primary job is investigating and determining whether maladministration by others has taken place must itself take care to avoid maladministration by delaying justice. If it does not, it will undermine its own role and credibility."
Reproduced with acknowledgements to BBC News.