The ashServ.exe is the main scanning engine in avast 4.8, so depending on what you are doing you are going to get spikes in CPU use as files are scanned, this however should quickly return to lower levels, unless there is a lot of activity going on.
Although this information relates to 100% CPU usage, you can check out the three points:
-- ashServ.exe 100% CPU - Vlk, always says that the guidelines for solving of the problem "ashServ.exe using too much CPU" has always been the same:
1. Check if the avast tray icon is spinning (while CPU usage is high) ?
2. If it is, click it (wait for the dialogue box to open), and check which file is being scanned (the Last Scanned field); the Scanned Count value should be increasing (spinning icon means a scan is in progress)
3. Find out which of the providers is scanning the file (click "Details" button and check out the Last Scanned value for each of the providers). The most common providers that may cause this are Standard Shield, P2P Shield and IM Shield.
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What are/were you doing when this happened ?
What else has changed on your system recently ?