Here is a video of my 83 reving. You can hear it when the RPMs drop. Is this the shutter valve?

http://www.youtube.com/watch?v=Jt4oWWMRgt0

 

Sounds like it. As the engine decelerates the shutter valve opens and then closes right before the engine gets back to idle. This is not always a smooth transition, causing a momentary high idle and then dropping to the correct rpms. I have had some luck smoothing this out with adjusting the idle mixture screw. When I adjusted the idle mix screw too far, the rpms would drop non stop to zero, stalling the car.

 

Sometimes it gets stuff making that noise and the rpms sit at about 1300. I have to let the clutch out a bit to drop the rpms and then it gets unstuck.

 

When the shutter valve goes bad it will have a distinct honking noise coming from the air cleaner. I would listen to the video but I am on dial up and I would be old before I got to it. Wait, I'm already old,lol.

 

Can the shutter valve get stuck all the way open? And stay at 1200 or 1300?

How distinctive is this honking noise?

Kev

 

Very!

 

My car does the same thing, so I put a piece of duct tape over the hole it connects to in the air cleaner. Problem solved!

 

Rats nest removal will fix this...
If you don't want to tackle it, you can just cap off the shutter valve alone. Very easy.

Good luck.

 

Unless you are in a area that you have to have emission testing done. The shutter valve is designed to shut off fuel during deacceleration to lean out the system.

 

my 82s does this every now and then but usually it bounces the idle between 750-1500 about 4 times and dies. i have replaced the shutter valve and rebuilt the carb and it still does this but it seems to be a fairly common problem with the 7s i have seen here in my area. i would adjust the idle and check the rest of your rats nest for other problems(if you havent replaced the vac hoses here now might be a good time...only 10 bucks and about an hour of labor if you do it right....just use a standard (flat head) screwdriver to break vacuum line seals....emissions equip on these is brittle after 20+ years of engine heat, oil and abuse). and seriously be careful not to put force on top of the emissions modules when doing this....i busted 3 emissions sylenoids and the little black egr looking thing ( i don't have an EGR but it looks almost exactly like one) when i did this....it was my first time though......

lemme know if you get this one fixed and lemme know what you did to fix it....also the shutter valve will honk (sounds exactly like the real horn but slightly muted) from the air cleaner when it is fully gone as well as making the engine sound much louder, possibly increasing engine temps( mine was burning old oil off of the engine cuz it was so hot) and you may also notice a stutterring or stammering when (if) it idles on its own along with some backfiring after car is turned off as well as accellerating ( added to the backfiring from decelleration). you may also experience a subtle loss in power during low end driving and a whole lot of headache from high speed driving) in addition to a slight lack of response from the accellerator pedal.

this was just my experience with my shutter valve going bad....i hope that it helped you in some way (i have to pass emissions here in CA so i had to keep all the **** stock for smog.... otherwise i would rip out the rats nest and be done with it...

 

sorry but idle mixture screw? which one is it? the idle adjust or the mixture adjust? just want to know for future reference

 

The "mixture adjust screw", appears I should have left out "idle".