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I am having an spasmodic problem with my car pulling up and loosing power although the engine keeps running. It has been sitting in the AA garage for a week and they cannot find the fault. March 11th it pulled up and I coasted around the corner and had the breakdown truck take it to garage and they could find no fault. I had an oil leak repair ($309.06) in February. On the 4 June it pulled up again but I was able to keep it going and this time the garage replaced the spark plugs and fuel filter and cleaner the distributer cap and air filter. Last Friday I got to the end of the road and slowed to turn right and it pulled up again and I leapfrogged my way around the back and home again. The manager rang yesterday to say they can't find the fault as they keep taking it out for a test and it is okay. Unfortunately, it only does it spasmodically. To me it appears to be a blockage of some sort. I have got to the stage I don't know what to do and I am very reluctant to drive it again as the last episode left me shaking like a leaf and I was in a quiet suburban area. It obviously can't stay at the garage.

Intermittent faults such as this can be a real headache, as usually all the diagnostic tests the mechanic can carry out won't pinpoint the problem if it isn't there at the time.
With the symptoms you describe, the problem sounds like it's related to fuel pressure. Replacing the fuel filter and doing the general tune-up work that has already been done would be the first place to start. To my mind, the next thing to consider would be the fuel pump, however it's a hard call to make, as you could spend the money on a replacement fuel pump which may prove not to be the cause.
I'm sure your garage may have already considered this possibility, but perhaps you could discuss it with them to see if they have checked fuel pressure.