Hi y'all. Been a few years since I've been sitting in an F-Body, so I'm struggling to re-acquaint myself with the whole thing in a jiffy. Alas, my recent purchase is something of a project (and I don't mean "project" as in "building it into a monster," more like "making it liveable again"). Thus, my query to the masses.

I'm running an '87 Formula Firebird with 305 4bbl VIN H and 700-R4, mostly stock/original, with a whopping 170k on the clock. The full tune-up list I've already gone through in the past week alone (mostly standard procedure preventative stuff):
New reman'ed QJet carb (previous owner, 1 month ago)
New mechanical and elec. fuel pumps
All new belts
All new fuel/coolant/vacuum hoses
All new filters/fluids from front to back
New plugs/wires/cap/rotor
New Baro sensor
New O2 sensor (by previous owner, unknown mileage on it)
Adjusted idle to 700 park/500 idle (it diesels forever when I shut it off if I let it idle any higher)
New cat (previous owner)

Now, being that I hooked everything up exactly as it was before whilest re-doing the vacuum lines, and since my Chilton manual is about worthless for vacuum diagrams on an '87 VIN H, I am ASSUMING everything's hooked up correctly. The car runs perfectly fine (aside from that dieseling issue related to idle), pulls strong, and cruises/idles smooth. From a cold start all the way 'till I reach operating temperature/closed loop, there's no "check engine" lights or symptoms or anything.

BUT ... soon as it warms up, I keep getting a Code 34, which comes up as "vacuum too high/low" in the manual for my code reader and my Chilton. Replaced the baro sensor, and in doing so, I noticed there's no vacuum line attached to it whatsoever, although there was some crumbly old foam stuff stuck underneath there (some kinda filter, perhaps?) As far as I've read from searching, no vacuum lines go to a baro sensor, only a MAP, and since I'm carb'ed and not TBI, then I figure that ain't the issue. No symptoms at all, aside from that glaring light, which I'm assuming would automatically fail me if I try to get this thing through emissions (which I'm kind of in a hurry to get legal). Being that my rear tires are WAY oversized and, thus, my speedo is off by about 10 mph, I dunno if my gas mileage is being affected or not.

Since it only happens in closed loop mode, it seems to me like it's a bad O2 sensor, but how would that cause a vacuum-related Code 34 (and not an O2 sensor-related code)? Also, the exhaust does SEEM to smell a bit rich, but I dunno if the Smog ***** will even give the thing a sniff at all if there's a SES light glaring at them, so I can't really verify that suspicion. About the only other thing I can imagine is if some other vacuum sensor has gone funky on me. It's almost completely asymptomatic, aside from that friggin' light. Any suggestions?

Many thanks in advance.

 

ROOF RATS!

I think I might've already found the source of this issue. I bought the car from a dude in the Tempe area, where there's lots of citrus trees and, thus, there's a LOT of roof rats (especially as of late). Roof rats are notorious for chewing holes in anything and everything, and they seem to have a strange affinity for plastic and rubber things. I already knew my Bird had been gnawed on a little bit, as there were distinct teeth marks where they'd almost chewed completely through the top heater hose and on the bypass hose going to the back of the intake manifold. However, I never thought to double-check all of the wiring toward the back firewall, where there was a bunch of tree debris n' stuff bunched up. After picking all that crap out of there, I saw what might be the source of my Code 34.

Apparently, some rats were trying to make a little happy home in that little nook between the fender and my brake booster, right underneath the vacuum sensor (which looks an awful lot like my baro sensor, oddly enough). Sure enough, they had chewed one gray wire plum through, snapped it right apart a little bit behind the connector, and they had also munched apart a couple of small wires grounded against the body nearby. (Jeez, they actually bit through copper wire! ) I re-established the connections they cut and then taped over the exposed wire spots they hadn't completely severed on a couple of wires to my wiper motor, and then re-set my ECM (for the fifth time in two days). I'll give it a run around and see if it keeps throwing a code, but I'm pretty certain this was the cause of it.

Thus, if anyone in the Mesa/Tempe, AZ area is having troubles with weird trouble codes and whatnot, give all your wires a second look. Roof rats might be making a snack out of your F-body.

 

BAH! Still not healed. Car had me fooled for most of the day. Didn't throw a code until just on the way home from work. Same code. Wires weren't the issue, after all ... unless there's some more chewed-through wires I can't see somewhere else. Looks like I may have to pay some monkey $60 to tinker with my toy, just to figure out what the heck's wrong...

 

Affixed to the underside of the hoos should be a decal that looks something like this:



Are all your hoses on the proper connections?

Are you getting a 5VDC reference voltage at the BARO sensor?