Tachometer bounces up before settling back down

Hi all,
92 Teg. Recently I've noticed that when I come to a stop, my tachometer would always bounce back up to around 1700 RPM before settling back down to
850 RPM (my IDLE).
Anyone knows what could be causing the tachometer to bounce up before settling down? Could it be a leak in one of the hose?
Thanx in advance.
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One common cause of this is a cooling system inadequately purged of air. The EACV (or idle air control valve) is cooled by the anti-freeze in your car's cooling system. That valve is a high spot on certain cars. Follow the manual to the letter on purging this system, and this may cure the problem. Getting the fan to come on twice may take 40 minutes of idling, so have a magazine.
Other sensors that feed into the car's computer may also be seeing inadequate cooling due to air in the system.
I had this problem at stops a couple years ago with my 91 Civic. Turns out I'd recently replaced the thermostat, introducing plenty of air into the system, and had not done a proper purge afterwards. A proper purge fixed the problem right up.
Vacuum leaks like you say could also be behind this. Other causes are possible as well. One step at a time...

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Mine would bounce up and down between idle and 1500 (accord). Mice had eaten a hole in the air cleaner element replaced that and also cleaned the thortle body very well. between those two it solve it.
Hootie wrote:

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