lack of power

[alan_rose]

i have a problem, my W reg 2L 16v omega is giving me a few problems it seems that some days she drives like the wind, but other days i realy have to push her
up to date i have hade the following repairs
camshaft sensor
lamda sensor
crankshaft sensor
egr
cat
piston rings
bigend bearings
all done by my local garage, who says that there is nothing wrong, there are no dashboard lights on, and she ticks over like a dream.
it is the lack of power which conserns me, i have had this car since 2003 and these repairs have all been done in the last year.
can anybody help please

[Martin_1962]

Air filter

Breathers

[alan_rose]

air filter changed last week, pipes changed on idle motor, also cleaned with carb clean.
any other ideas, cos i am at a loss

[JasonH]

Blocked exhaust? Makes a big difference.

[alan_rose]

that is fine, the tone is as always, but the power sounder is being activated when i turn the engine off every 4th time, and the power problem seems to be linked,
i.e. prior to the power sounder being activated the power is there