Originally Posted by dnarby

Thanks for the link, I'm suspecting I have some sort of vacuum leak now (I also replaced the flame trap and fiddled with the tube going down to the oil separator in the process).

This is a bit strange: Replaced IAC/flame trap/plugs/wires/cap/rotor/air filter, cleaned TB and intake hose (did not mess with the air sensor, don't have the proper cleaner for it yet), checked/repaired every connection/ground that was obvious.

Air flow sensor says BOSCH, it's an '89 N/A.

My brick now idles rock steady at ~700RPM on start up, after driving it for awhile the idle starts to bounce between 200-1000.

At this point, if you rev the engine to 5-6000, it takes an abnormally long time to return to the (bouncing) idle, and it does so by idling down to ~4000, hesitating there, then ~3000, hesitates again, ~2000, etc.

Hopefully this will help solve the original poster's problem as well (not wanting to threadjack).

Originally Posted by jagtoes

By the way have you checked the diagnostic box to see if you have any codes.

Originally Posted by jagtoes

Also at cold start like in the morning you should idle at around 900-1000 RPM until it gets warm.

Originally Posted by jagtoes

Also if the TPS is not adjusted correctly you'll have a problem at idle. Last is the issue with the throttle adjustment screw. So after you check for vacuum leaks then start with the base idle adjustment with the IAC disconnected. Get a new idle adjustment screw at some auto or hardware shop.

Originally Posted by pierce

ah, THAT sounds like your throttle body is gummed up or sticking, and not closing consistently.

pop it off, and hose it down with a solvent/cleaner while manually working the throttle plate open/close. even get in there with a toothbrush and some WD40 or something, and scrub off any deposits and buildup.

Originally Posted by pierce

then make sure the idle position switch consistently clicks just before its fully closed.