Volvo Repair: Volvo s40 1998, volvo s40, vapor lock

Question
I have recently had a problem with lack of power - down to a crawl, I had a new petrol filter installed 2 months ago and mechanic advised old one was completely blocked. Has been running fine except that it idles roughly, but apparently that is a common volvo fault, but recently it again, lost power,I couldn;t drive faster than 10kms ph the weather was very hot on that day  - the mechanic could not find anything wrong and had it in the repair shop for 3 days driving it each day, but then it was cooler. He seemed to think in hot weather that the fuel evaporates before it can get through. Any ideas

Answer
Sue, It could be vapor lock but highly unlikely.  Not sure if the 98's are different than the ones here in the U.S.  We only got them in 2000.  It may be the ECT sensor but then again, without running a battery of tests I would only be making an educated guess.  Roger