85 318i fluctuating idle problem

[Rigmaster]

Trying to help a friend figure out a problem with their 85 318i.

Car runs well, but idle surges/fluctuates very rythmically. I unplugged the ICV and it made no change, so I thought the ICV must be dead. So, I found a nice new-looking ICV at the local pick n pull junkyard the other day, and we installed it tonight. BUT, it made no difference. So, I thought maybe the ICV control box (green box above the glovebox) might be the culprit, so we swapped it out and it made no difference.


I tried turning the adjustment screw in both ICV's and it makes no difference.

I've done a check for vacuum leaks- basically just eyeballing everything, pushing and pulling the hoses, etc and found nothing obvious.

When I take the oil filler cap off, the idle still fluctuates.

Car was a 1-owner car before my friend bought it, so it's been fairly well maintained- but it IS 25 years old.


Thoughts??


Thanks in advance for any input- I'd really like to be able to help get this car running right.

[bmwm42]

Try the penny trick on the icv get a bunch of pennies and start drilling the center with different widths until you get it just right also check maf

[Rigmaster]

Try the penny trick on the icv get a bunch of pennies and start drilling the center with different widths until you get it just right also check maf

Yeah, I'm planning to try the penny trick, but it'd be nice to figure out what's really wrong with this thing and fix it right- if possible.


Now I'm sort of thinking it could be the TPS- but I don't have a spare handy to test with. Guess it's back to the pick n pull to find one.

[Rigmaster]

Been doing some online searching for similar problems, nothing concrete so far, but it looks like the 02 sensor *could* also be a possibility. Then there's the Idle Speed Stabilization Relay, which *sounds* like it might have something to do with stabilizing the idle (ya think??)....

;)