Working on my brother's LG-4 85' IROC yesterday between thrash session putting in the new MiniRammed 400 into his 87 GTA. We finally fixed an annoying idle miss that has plauged his car since he bought it. There is a vacuum line going from the intake manifold behind the carb over to a rectangular box bolted to the firewall above the power brake booster. We suspected a vacuum leak since rebuilding/readjusting the carb made no difference in the miss and the ignition is all new. Pinching various vacuum lines with a pair of pliers we discovered it. Idle immediately went dead-smooth and slowed down a few hundred. This "box" has a 7/32" line going into it and a tiny vacuum line coming out going into the wiring harness that goes through the firewall. Eventually we figured out it was the line that runs the vacuum doors in the ventiation system under the dask. Most GM cars have a small round bulb on the pass. fender to filter out vapors, store vacuum and incorporate a one way valve. They almost never go bad. Not the 85. Whatever ruptured insde this box was allowing the large vacuum line to suck in a LOT of air and give a dead miss at idle. Got a bad idle miss? Check out this vacuum box- yours could have gone bad, too.

OMG!

Is it this...


The picture looks like crap - but it is about 8" long and half cylinder shaped - I always wondered what that was for.

I've had the same problem for a long time! Even after a full tune up and vacuum leak check around the carb I couldn't find anything!


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1985 Z28, Jasper Class 1 350, Edelbrock Performer intake, Dual snorkel air cleaner, K&N, Edelbrock headers, Catco 3" cat, Hooker 3" cat-back, Richmond 3.73's, built 700r4 w/Darrell Young 2400 stall TC, JET Stage 2 chip, Hypertech coil, Lakewood LCA's, Powertrax locker, SSM subframes, Centerline Auto Drag's


[This message has been edited by Marc 85Z28 (edited July 29, 2001).]

Bingo! That's the one, man.

Have problem, will check.

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`85 Z28
Bosch Platinum +4s & a nice stereo
Otherwise stock.

Don't ever be: Found On Road Dead!