My 1985 GSL-SE with an original 13B has a slight "misfire". I don't actually think it is a true misfire because I've already replaced the spark plugs, cables, cap, and rotor and that didn't make a difference. It has the intermitten, not-quite-predictable rumbling like if I push in the TPS without actually changing the throttle plate position. The idle moves ever so slightly between 800-850RPM. The car runs fine, there isn't really any sign of misfire above 2000RPMs, and I've already done a TPS adjustment. Just every second or so (it's not perfectly even), there is a slight "misfire" at 800RPMs (idle). When I drive it, there is no sign that anything is wrong with the car: no unusual surges or anything anywhere even up to ~6000RPM. Seems to be strictly an idle issue.

Are there any other low-effort things I could check at all?? Thank you!!

 

try turning up your idle and see if it goes away.

 

when the car is cold and its in fast idle mode, the problem does not go away.

 

check vacuum lines, its possible you have leaky injectors its not unheard of.

 

advice on how to check the vacuum lines? carb cleaner?

 

look at all your vacuum lines and see if they look broken, brittle, cracked or are super hard which usually crack easily. if you have a vacuum leak and you spray carb cleaner, it will cause the car to hesitate. I use a smoke machine and smoke the entire system. if i see smoke leaking i found the problem. it comes in real handy.

 

thank you for the help! ill check for vacuum leaks.