For several months now I have put up with a throbbing idle ( 100-200 rpm ) 3 or 4 times a second. Only with a cold engine or if I shut it down and start it back up warm or operating temperature. Cold it would stop as soon as it was in drive. Warm or operating temperature it would throb in drive also and then after a couple minutes suddenly stop. When I first bought the car it would throb three times immediately after starting for just about a second, then be fine the rest of the day. I have replaced the intake manifold gasket ( cracked in many places) Cleaned the idle control (filthy) and throttle body(filthy) using a new gasket. Checked the tps adjustment and also that the computer is seeing the switch input (ok) . No vacuum leaks. Good clean grounds on fenders and intake. Idles fine if you disconnect the hose from the manifold to idle control and use a thumb to regulate idle speed.

I always suspected the idle air control after all this, never a code...Until this morning. Left work fine in drive. Then a block away it starts surging wildly at idle in drive about 3 times a second and severely jerking the car.
Checked for codes and got a 233 ( idle control valve closed ) Regina system.
Would it be safe to say the idle control is bad especially after this? I would have replaced it earlier if I could find a used one cheap (10-20) But auction place ones are 40 to 50 bucks and new ones $315 on Eeuroparts. I would rather buy new than overpay for a used. Where can I get a reasonably priced iac new or used? By the way, I restarted it a half hour after this episode and it seems to be back to its "normal" throbbing. Many thanks in advance for any help