CyCloNe!

Hey guys I'm trying to understand my car a little better, when it's on idle it got a little vibration and then it will have like a stumblish vibration after a few seconds and repeat the cycle. Any ideas? As far as I know underboost and accleration its great doesn't surge.

I've replaced:

Injectors
Rotor Button
Cap
Plugs
All vac lines and Boost Hoses
ISV
TPS

My vac is a little low so far all I can figure would cause it is idle adjustment or new throttle body seals. Every other vac line is nice new and tight (secure). I do have a Lightening MAF with Rogue Tune and my vac is around cold 11/12hg warm 13/14hg at 900ish RPM

Copilot

Mine was doing that when I bought it - turns out the seal on the idle screw in the throttle body was rotted - I replaced the screw for $7, and it ran like new again.

CyCloNe!

Ironically you said that, I just adjusted my idle screw and I got a little more vac but was still doing it, I will go ahead and replace it and see if that's the issue.

86 951 Driver

Did you rebuild the throttle body?

Copilot

Nope, just did the screw. Everything else was fine - I am pretty sure it was rotted/chipped away due to the previous owner messing with it, not due to age.