jusjofok Posted May 28, 2009 Share Posted May 28, 2009 Hey guys, have a question for you on my 280ZX 2+2 NA. I went for a drive yesterday and when I got to the stoplight on the second mile the car wouldn't idle below 1500 RPM. I went back home to mess with it but nothing I did would make it idle down, I checked connections on the temperature sensors in the thermostat housing and everything looks ok there. I also removed the AFM, flapper closes all the way. I didn't change the idle screw and it is going all the way to the screw. AC was off the whole time. Any ideas where I should go from here? Thanks, Justin Quote Link to comment Share on other sites More sharing options...
RUZN Posted May 29, 2009 Share Posted May 29, 2009 Un-Metered Air.. Somewhere you have a Vacuum hose disconnected and its getting some nice fresh air into Manifold. Check all your connections. you should be able to hear a Hissssssssss probably if it is a Vacuum line or EGR tube open/cracked/rusted/unplugged.. ect ect specially if its a solid 1500rpm.. Quote Link to comment Share on other sites More sharing options...
woldson Posted May 29, 2009 Share Posted May 29, 2009 ^^Agreed. Quote Link to comment Share on other sites More sharing options...
jusjofok Posted May 31, 2009 Author Share Posted May 31, 2009 Found out what it was today, there is an air bleed valve (not sure of its purpose) on the bottom of the intake manifold that I could pinch off vacuum to and the car would idle normal. I gave it a good tap with a pair of pliers and it seems to be working fine now. Now, I suppose it will do it again some day and I should probably know what it is supposed to do. It is on the bottom of the intake manifold and has a small vacuum line that comes from the top of the manifold that goes to it, it also has a large air line that comes up from it along side the manifold and tee's off and one goes to the throttle body, this line is about 7/16 ID or so. It has a pressed steel canister with a nut on the bottom of it, it has 6 screws that hold the pressed steel canister to the aluminum housing, the whole thing is held on by two 10mm headed bolts. Any ideas what it is?? Thanks Justin Quote Link to comment Share on other sites More sharing options...
islanddozer Posted June 2, 2009 Share Posted June 2, 2009 its your cold start valve. I just reread your post and I thought you had said it was above the intake. The underneath valve is the BCDD (boost controlled decleration device). Read the Haynes manual and it says to be done by qualified Datsun mechanic LOL I have removed and cleaned many. Just mark the plates by scribbing a line disassemble and clean. Don't dump in fluids until rubber is removed. good luck. Still think the cold start valve. Quote Link to comment Share on other sites More sharing options...
280zx 2by2 Posted June 3, 2009 Share Posted June 3, 2009 he might be talking about the PCV valve if he tapped it with a hammer and it started working... its on the bottom of the intake manni and has a large vacuum hose on it Quote Link to comment Share on other sites More sharing options...
islanddozer Posted June 3, 2009 Share Posted June 3, 2009 It is on the bottom of the intake manifold and has a small vacuum line that comes from the top of the manifold that goes to it, it also has a large air line that comes up from it along side the manifold and tee's off and one goes to the throttle body, this line is about 7/16 ID or so. It has a pressed steel canister with a nut on the bottom of it, it has 6 screws that hold the pressed steel canister to the aluminum housing, the whole thing is held on by two 10mm headed bolts. Any ideas what it is?? definatly not PCV pcv has one hose and is not bolted to mani Quote Link to comment Share on other sites More sharing options...
280zx 2by2 Posted June 3, 2009 Share Posted June 3, 2009 It is on the bottom of the intake manifold and has a small vacuum line that comes from the top of the manifold that goes to it, it also has a large air line that comes up from it along side the manifold and tee's off and one goes to the throttle body, this line is about 7/16 ID or so. It has a pressed steel canister with a nut on the bottom of it, it has 6 screws that hold the pressed steel canister to the aluminum housing, the whole thing is held on by two 10mm headed bolts. Any ideas what it is?? definatly not PCV pcv has one hose and is not bolted to mani yeah its the bcdd that hes describing but tapping on the intake manifold could have loosened up the pcv, because I don't see how a bcdd could effect idle unless one of the vacuum hoses has a hole/crack... could just go outside rev it and see if the bcdd is actually working Quote Link to comment Share on other sites More sharing options...
RUZN Posted June 4, 2009 Share Posted June 4, 2009 yeah PCV valve can get gummed up by deposits and when engine is cooling that rubberized oily crap starts to harden and sticks the valve.. Quote Link to comment Share on other sites More sharing options...
jusjofok Posted June 4, 2009 Author Share Posted June 4, 2009 Its the BCDD, I found a diagram of it in one of the manuals. The funny thing was that I could pinch the small line from the top of the intake off and the car would idle down. I removed and disassembled it, cleaned and reinstalled it and everything seems to be working fine now. I just marked the adjustment nut stud on the bottom and put it back where it was after the cleaning of the entire valve. The diaphrams were nice and pliable so I don't know what was up with it but it is working now. Thanks Justin Quote Link to comment Share on other sites More sharing options...
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