so when i start up car the idle oscillates... only in park or neutral, soon as i put in gear (R, D, etc) it settles down to normal...

90% of the time this oscillation happens, but not always. up...down...up...down...

if i let it sit in park, after a while it will usually calm down, but it takes a while.

ive replaced the IAC already a few months ago and it didnt help. yes i did the reset procedure too..

any ideas? be gentle im still learning.

 

Maybe a tune-up? Maybe a plug or plug wire is starting to go. Seen nobody answered your post so I thought I would try to help, I hate it when nobody answers my posts....

 

i thought of that but would that cause it to be in P & N only? that was the part that seems weird to me.

the plugs and cap and rotor and within a year new. wires i dunno. its been doing this for a while but i didnt get around to fixing it since it drives ok.

 

sounds like it could be a vaccum leak.. kinda weird it only happens in neutral or park though... just a thought..

 

yeah i was wondering about vacuum too. but i dont know very much about how it functions and would relate to my problem?

i think some of my tubes are quite old and decaying seems like.

 

OK well i changed all the vacuum tubes and its still a surging idle in park and neutral.

any more ideas? stuff i can check?

 

you could also be losing vaccum around the intake gaskets, throttlebody/carb, and also the power brake booster could on its way out.. to check for leaks around the intake and tb/carb grab a can of starting fluid and spray around the surfaces with the engine running, if idle increases while spraying you've found your leak.. to check the booster you disconnect the vaccum line and plug it and see if the same thing still happens.. if not that may be your problem... maybe someone else has other suggestions.....

 

I use to have that problem with my car, cant recall if it happened in drive or not.

But, I came to find out it was my AC Compressor cycling on and off, what you may want to do is watch the compress or clutch and see if, when it cycles on the idle drops down..

Just another idea I thought Id toss out there.