shark revs too high until i bump it down...any suggestions?

[BoiseShark]

The 79 is running great but I have one problem (actually many, but one for this post). My shark idles at about 1000 rpm, but when I come to a stop it will idle at about 1500 to 2000 rpm until I rev it up quickly and then it will drop down to (normal) idle. I realize I should be about 800 rpm, but she really likes 1000. I just need help determining why it's not returning to idle on her own without being reved first. One rev up to about 3000 will bring it back down to 1000, but if I just push in the clutch and come to a stop, it's stuck between 1500 and 2000.

Any ideas?

Thanks in advance for your help.

[Danglerb]

Throttle linkage sticking?

I don't think the 79 has any special active idle control, maybe a vacuum limiter?

[AirtekHVAC]

perhaps a gummed up butterfly under the spider...mine was gooped shut...

(Why are we talking bugs here?)

[DPW928]

Make sure there is some slack in the throttle cable. If too tight at idle it can be adjusted at the firewall. Also, the cruise control cable can become sticky and cause this problem, especially if you don't use it. BTDT

[Brenton928S]

I had the same problem on my '82 S and i found it to be the throttle linkage at the throttle body going over centre and holding the throttle open a bit more than it should be. A simple adjustment of the linkage cured it and all is good now. Idle RPM should be at around 1000rpm.

[JK McDonald]

Hey Boise Shark, On some of the early CIS cars there was an auxiliary air device that can cause a hang up or failure of the throttle to return to the preset idle. The aux-air device is usually mounted very close to the air flow meter/throttle assembly. The symptom that I’ve seen is that you can blip your accelerator and the idle will often fall back to the correct point. One other quirky symptom is that if you “lug” the engine down using 1st gear, the vacuum signal inside the aux-air device is sufficient to overcome it's internal spring tension and force the idle back down as well.

If you have this aux-air device, it will be a fist size bell shaped looking gizmo with a 5/8” air hose connected to one end and another 5/8” hose connected to it's side. There is also a small 1 /4” hose that plugs in over a small vacuum orifice within a snout. The snout has two flat sides (under the 1 /4" air hose) for making adjustments. If the aux-air device is out of adjustment - simply remove the small hose, loosen the lock nut at the base of the snout and turn the snout a couple of turns in. I use a small crescent wrench for setting the internal spring tension. Snug down the lock nut, reconnect the small air hose and take’er for a run.

Perhaps someone with a CIS vehicle could add a photo of this aux-air device. I do not currently have anything with this component installed.

Good Luck, Michael

[dcrasta]

Get some carb cleaner and some gum cutter. Spray the bejesus out of your linkages , aux air control device, butterfly, etc.

Follow up with some wd -40 (carb cleaner leaves things unlubricated). This would be a good time to lube the throttle cables.


Return with results.

[BoiseShark]

Haven't been on in about a week. Thanks for all the suggestions. I'll put them all to work and see if I can't get a cure and will let you all know how it comes out.

JK, I think I know what your are talking about. The 5/8 airhoses go directly into the air intake on the lower plenum (the four inch round chamber that hits the bottom of the spider)