[baseballZ]

Do you guys want to give me the most common reasons why my 78 280Z probably will not idle down quickly when you take your foot off the accelerator. It will idle at 1000 rpm's but when driving it goes to 2000 between shifts. Sometimes if you hold the clutch down for 4-5 sec and coast it will come down. What do you'll think this likely is...?

 

[yo2001]

vacuum leak. may be from your air regulator?

 

[ConorP]

Do a search here for "BCDD" and "Dashpot", that will answer everything.

ConorP

 

[silver77280z]

Im having a similar problem. its a 2k as well. im not having much luck searching for dashpot and bccd. Can some one help me out. I went through every vacum line and none seem to be leaking.

 

[DylanZ]

Here's another possibility--- If your heater is turned on, it will idle high! It gets me every once in a while, then I remember to flick the switch. Do all injected cars do that.... or mabee I have a vaccume leak in my vent valves... I don't have defrost... hmmm... ****, I don't want to pull the dash

Dylan

 

[ConorP]

baseballZ: That's exactly what the BCDD was designed to do.

Most have failed or stuck by now so they don't do this at all, others delay too long. Their is an adjustment screw at the bottom that sets the vacuum level that it turns off at. Some people have plugged the air inlet hole in the BCDD (by taking off the AFM to reach it.) Others have properly repaired them, still others have disassembled them and replaced the gasket with a solid sheet (so as to prevent it's action.) I even heard of one guy that just applied a switched +12 volts to the BCDD to prevent it from operating ... but I think I'd rather plug a hole then butcher the electrical.

Of course their are some other things to check. The mechanical linkage itself, try to push the throttle body closed. The air regulator, pinch the large hose ... the engine should stall or strongly stumble

If you're still in doubt or have trouble with these instructions, then you'd do yourself well to buy a FSM.

ConorP

 

[baseballZ]

Thanks all
Conor , I do have a FSM (on disc)
I adjusted the BCDD (took out the little plug on bottom and turned ) and although it helped, it has not solved. I was scared to turn too much (Only about a half turn) so maybe I'll give it a little more.I do have a leaking heater valve inlet...could this be a source of vacuum problems.Seems like it would only do while heater was on,but it does it at all times...

 

[kiwi_260z]

Are your carbs balanced? They can do funny things when there not in sinc with each other, because one is trying to run its three cylinders faster than the other three cylinders, so one carb ends up 'carrying' the other. If your carbs are out of balance by alot, you will be able to see it. Look at the linkages between the two carbs. The front carb should be activated by a linkage from theback carb, and the conection is made via a small adjuster screw. If you can see that this screw is not touching the front linkage when you are not on the gas, or you can slip a piece of paper between the screw and the linkage, this is your problem. However, there are other adjuster screws for balancing the carbs, and they have to be tweaked in the right order, so if this turns out to be your problem, make another post and ill describe it.

 

[baseballZ]

FI-no carbs....