Breathing apparatus used by the trust's hazardous response team was not properly checked and a defibrillator had not been charged.
The Care Quality Commission report also said the trust was not meeting response times for the most serious 999 calls.
The trust said concerns about equipment were addressed immediately.
The report found that less than 71% of emergency call-outs were responded to within eight minutes between last April to September. The government target is 75%.
The service has previously been criticised for not reaching national response times for the most serious of calls.
During January and February, inspectors visited 14 ambulance stations including ones in York, Huddersfield, Leeds Central and west Hull.
It found infection control practices were not always followed by staff and procedures for the disposal of clinical waste was concerning.
A large number of ambulances were found to be dirty on the outside and the general cleanliness inside was highlighted as a problem.
Inspectors flagged up areas of outstanding practice at the trust, including a campaign which gave life saving first aid training to more than 12,000 pupils.
Its emergency operations call centre was also praised as was the work of mental health nurses in giving support to patients.
The trust has now been told it must make improvements.
Rod Barnes, chief executive of the Yorkshire Ambulance Service NHS Trust, said it accepted the report raised issues which needed tackling.
He added: "We have continued to make progress in all areas over recent months and have a clear plan of action to maintain this improvement."
Life-saving equipment used by Yorkshire Ambulance Service paramedics for major disasters was out of date when it was inspected by the health watchdog.