My '89 IROC 305 TPI has developed a couple idle problems.

First: 9 times out of 10 when cold it's WAY too high. My tach isn't real accurate, but guessing at least 3000 rpm. Just shutting it off and restarting it right away usually results in a normal cold idle speed...but not always.

Second: when warmed up/in drive/stopped (ie at a stop light) it starts idling very rough - almost 'lurching' and like it's about to stall. I have to put it in park and goose the throttle to keep it at a steady idle, which really sucks when waiting in traffic.

There's no scanner error codes and when I took it to shop I've trusted/used for years, they supposedly found a vacuum leak in the manifold gasket. However after they replaced it the problem persists. Brought it back again and this time had the injectors cleaned. Again they thought the problem was solved, but I'm confident they didn't wait long enough to get the really rough idle that occurs only when fully warmed up.

Looking at my Chiltons, I'm almost thinking it's the EGR valve based on their description of symptoms of what can happen when it's bad (and I also some mild knocking on hard acceleration, which is shown as a symptom of bad EGR too). Any ideas what may be the culprit? I'm hesitant to take it back to the same shop and have them tell me it's yet something else.

Thanks