Small RPM cycle at idle

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Small RPM cycle at idle

Post by Neu »

Hey y'all,

i tried searching but couldn't find anything related.

I have a mild rpm cycle at both cold and warm idle. My idle sits around 1100rpm once warmed up. Occasionally it will "cycle" about 100-200rpms. They're quick little cycles.

Any ideas? It's probably an easy fix.

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My tercel:: none currently, 7 previous
Location: bc, canada

Re: Small RPM cycle at idle

Post by dlb »

Have you checked all the vacuum diaphragms to make sure they hold vac? I can't remember which (if any) have vac directed to them at idle, maybe the upper one on the dizzy? Probably a good idea to check them all while you're at it though.

Long ago, I remember 4wdChico had a rpm cycling issue and it wound up being related to the charcoal canister. There was a whole thread about it but I can't find it now, just this post where he talks about that same problem:

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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Small RPM cycle at idle

Post by Petros »

sounds like a vac leak. Visually look over all of your vac lines that they are routed correctly and there is no visable cuts or damage. Than check all your vac lines and gaskets for a leak using stater fluid or carb spray, give it little short puffs at various places while it is running, listen for an temporary increase in rpm. usually that will find it.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
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