The carbed version of the 2.8L is the engine from hell...... I have one in an '85 S10 and there are a bazillion places for vacuum leaks which will cause a crappy idle. I had to replace all the vacuum lines as they were so badly deteriorated. Get the diagram and go through systematically replacing and reconnecting any plugged or disconnected vacuum lines. This is an old technology smog engine (it uses vacuum signals to control most of the emissions functions). While you're at it, replace the EGR valve. My engine had the EGR disconnected ( the P.O. told me it needed premium gas so it wouldn't ping....no duh..... pull the EGR and the engine will run like crap and use expensive gas in the process); when I reconnected it, the engine would die at anything above idle so I bought a new EGR. There are also two vacuum operated valves used to control the the A.I.R. system (those tubes connected to the exhaust manifolds); one is on the passenger side, sits up high and has four or five hoses coming off of it. The other valve sit back on the divers side next to the EGR. On my motor both these valve had leaking diaphragms in them so not only did they not function, but they created a big time vacuum leak. Both of these valves are still available from your Chevy dealer (they will cost some coin). After I got all the vacuum hoses and new parts installed, the engine ran (and still runs) quite well...and passes it required emissions test. Good luck in your quest......
mike
'00XJ
'85S10
