IDMan.exe or IDMGrhlp.exe process uses a lot of computer's CPU (or memory). How to stop it?
1. The problem may be caused by conflicts between IDM and other applications. It can be some FireWall/Antivirus/InternetSecurity application for example, which controls all network traffic and all disk activity. When IDM wants to read/write any data, security programs first pass all data through their internal buffers where they scan data for possible viruses. This way they always go-between IDM and real file on hard drive two times (for read and write processes) and can slow down the whole procedure greatly. Please check your settings in such applications and try to add IDM in the exceptions list if they have some. Also note that IDM cannot in any way bypass a security program when downloading or saving files, and this problem does not depend on IDM.
Maybe you have some application that has such function and you do not even know about it. Also, please note that some Antiviruses and other security applications keep controlling everything even if you disable them because they still have their drivers in memory that do this job in background. This why, you need to uninstall them TEMPORARY, restart your computer and check if problem becomes any better. If it is solved, then problem is definitely caused by that application. You can try to contact its developers and ask them for solution or try some other FireWall/Antivirus/Internet security application. If it does not help, look for another application on your computer. It may have something like "Security", "Protector", "Defender", "Spyware Remover" or "Cleaner" in its name.
In addition, some FireWalls and Antiviruses may be not ready for Windows Vista, Windows 7, Windows 8/8.1 or Windows 10 and work incorrectly. Or maybe some application is stable with Win 32 bit system but not fully compatible with Win 64 bit system. In such case you cat try to use another security application instead.
2. Many firewall and antivirus programs give IDM maximum access rights on downloading and writing to disks during first IDM installation. But after IDM updates, security software may see that IDM executable file has changed (read details) and starts to block access or turns on detailed download/write verification which can cause high CPU usage without user notification.
3. Also this problem is possible if you used some crack for IDM (read details). After installing the genuine version of IDM and registering it with a valid serial number problem should disappear.