I have a 1990 Accord Ex Auto. and just resently i started to have problems with it idleing. The car will stay running but the thing is the rpms goes up about 500 and back down 500 and continues to do that til the car is put into a gear. it first started doing that when i rav the engine up from a cold start but now when its at running temp. it does it only when its in park im not sure what it is but i hear that it might be the oxygen senor
Thanks

 

It could also be the rear motor mount, that uses vacuum

 

Clean out your IACV and also check all vacuum lines are hooked up.

 

make sure ur idle is adjusted properly ,,if it is too high the rpm will surge..........also chk vor vaccum leaks, also remove the top cover on the fast idle valve and turn in the big valve ,,,try those see if it helps