Yaris acceleration and stalling issue after clutch replacement

We had a new clutch put into our 2006 Manual Yaris YR about 6 weeks ago.
Since then we have had intermittent acceleration  issues after the car has
been driven  and the engine is warmed up. Take off at traffic light at times
has been very slow with car attaining 11-12kmsph for 30-40 metres before
accelerating properly. We also notice it tends to stall when stopped unless
we pump the accelerator. The problem doesn't show up on short 2-4km
drives only after its been driven some distance and quite warm. Its scary. A
retired mechanic friend suggests it could be due to damage to Vacuum pipes
or intake throttle box when the clutch was installed or fuel filter. The RAC
mechanics who fitted the new clutch said they cant find anything wrong
despite us returning it 3 times. The first time some adjustment was made but
as hubby drove away a red warning engine light came on . He took it straight
back and they switched it off and left it at that. Ran a bit better but problem
still occurs intermittently. When I took it back again they said nothing was
wrong despite the issue recurring . Help any suggestions appreciated as it
feels unsafe to drive.