Staff shortages and weaknesses in consistency, accuracy and timeliness of inspection reports have all been flagged up as areas of "concern" by the Public Accounts Committee.
Chairwoman Meg Hillier said there was an "alarming lack of attention to detail" when reports were prepared.
The CQC - set up six years ago - said it was proceeding with improvements.
The CQC's inspection programmes for hospitals, primary care and adult social care services in England are all behind schedule, the MPs' report said.
It was concerned by the CQC's ability to respond quickly and effectively to information received from patients, staff and whistleblowers.
On one occasion an NHS trust told the committee it found more than 200 errors in a draft CQC report, including data inaccuracies.
"The fact these errors were picked up offers some reassurance but this is clearly unacceptable from a public body in which taxpayers are placing their trust," said Ms Hillier.
The cross-party committee also said the regulator had "struggled to recruit inspectors and analysts" and as a result it was "not meeting the trajectory it set itself for completing inspections".
By mid-April the vacancy rate was 34% for inspectors, 36% for senior analysts and 35% for managers. Staff turnover in 2014-15 was nearly 8%, which is higher than the CQC's 5% target.
And the MPs warned that the CQC was not ready to assume new responsibilities for assessing the efficiency of hospitals in April 2016.
"Recruitment at the commission is going too slowly, meaning too many members of the public don't have up-to-date independent information about the quality of services provided," Ms Hillier warned.
"It is vital the public is clear on what the commission has actually inspected and when. If the commission is to properly fulfil its duty to taxpayers we must see improvements in the way it collects, acts upon and publishes information."
The MPs did also acknowledge that the CQC had made "substantial progress" since its previous report into the regulator back in 2012.
David Behan, chief executive of the CQC, said: "We have always maintained that there is more we have to do, in particular with regards to improving the timeliness of our reports and inspecting all health and adult social care services.
"These are not new issues and we have been working hard to improve our performance. We have reported on our progress in public every month and we will continue to do so.
"What is essential is that we do not take any shortcuts, which could compromise the quality of the important work that we do."

Jayne Ludlow's side are preparing for home qualifiers with Israel on 15 September and Austria on 20 September.
The inclusion of Seattle playmaker Fishlock is significant as she was pondering international retirement.
"We're looking forward to the next campaign, which is really important for us," she said.
Fishlock hinted she would retire after Wales' failure to reach next summer's Euros but the 29-year old is now targeting another campaign.
"We're really excited," said Fishlock. "We haven't been together for a while now and we always enjoy being together.
"Friendlies are always important. The result is not the main thing - it's about what we get out of it and hopefully we can get good things out of this one.
"The team spirit is good, it's always good. It is fun."

The man, in his 20s, was pronounced dead at Fairfax House in Livesey Close, Kingston, at 08:00 GMT. His death is being treated as unexplained.
London Ambulance Service was initially called to reports of a injured man at the scene.
Nearby homes have been evacuated as a "precautionary measure", the Met Police said.
The Care Quality Commission, the health watchdog in England, is "not yet an effective regulator", MPs say.
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Jess Fishlock has boosted Wales women ahead of Friday's Republic of Ireland friendly as they warm-up for their UEFA European qualifying campaign.
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A man has been found dead at a block of flats where a "possible noxious gas" was detected.