Sl!pstream

iTrader: (1)

As the title states, I have been having issues with the idle on my entirely stock '86 N/A. I've done a lot of reading about poor idling and I have tried to troubleshoot it to the best of my abilities without asking for help here, but I seem to be getting nowhere, so I figure it is time to just ask. Here is what I have observed so far:

The majority of the time, it is just a high idle (usually about 1100-1200 when warm). I have however noticed that the idle will sometimes pulse between 1300 and 1700 rpm or so on a cold start. The pulsing goes away after the engine has warmed up a little bit. If the engine is heatsoaked, the idle will be around 800 when I start the car until I touch the throttle, then it hangs up high again. For example, if I drive the car to the store, shop around and then come back out and start the car, it will idle low and smooth at first. The idle doesn't always hang up high though, sometimes the rpms will continue to drop back to where they are supposed to after releasing the throttle, I can't think of an explanation for it. Below is a video link showing the high idle.


You will notice in the video that I can get the idle to lower a bit if I forcibly try to push the throttle closed.


Here are some things are have checked/adjusted:

TPS: calibrated and in spec via resistance method when the engine is warmed up, reads within spec throughout the full range of motion of the throttle. Did the calibration with the initial set coupler jumpered (also tried it unjumpered just to see if there was any difference, which there didnt seem to be).
Idle screw: when I tried to adjust the screw, I found that it is completely bottomed out. I cant lower the idle any more via that method.
BAC: seems to be working, can hear a click when A/C is turned on, and idle doesn't change if I pinch any of the hoses coming off the BAC.

diabolical1

iTrader: (3)

well, i encourage your eliminating as many possibilities as you can. however, have you tried replacing the throttle return spring? if it idles and behaves normal when you manually return the throttle, and all seems well until you start actuating the throttle from the pedal, then it may just need adjustment or a tighter spring.


EDIT (responded before watching the video)

you may also want to check the timing just in case.

misterstyx69

iTrader: (142)

you know that you can adjust the cable to the throttle body.that may help.
Have you inspected the plates on the TB yet to see if the inside of the TB is dirty and preventing it from fully closing so it can idle??

Sl!pstream

iTrader: (1)

Thanks for the responses. Today I pulled off the intake tube and inspected the butterfly valves inside the throttle body. Below is a video of what I have observed. The lower primary butterfly is not returning to the proper idle position, as to why that is happening I don't know. I'm going to have to do some further inspection, the idle return spring being one thing I will look into. I'm also wondering if maybe the fast idle cam or thermal wax unit is operating properly. In the end I will probably end up pulling off the TB and cleaning it out and checking the clearance and movement of the butterflies, since that is now seeming to be the actual culprit.

Sl!pstream

iTrader: (1)

Sorry for the necropost, but I wanted to give a small update.

The other day I tried spraying starter fluid around the vacuum lines to determine if there was a vac leak causing my problems. The idle would not change at all so I'm pretty sure its not a vac leak. After talking to another owner who had a similar problem with a hanging idle and hunting around 1500 rpm, more and more I am suspecting the fast idle cam may be getting stuck somehow. Today I may try to tackle pulling off the throttle body and inspecting the thermowax unit. Probably clean out the BAC while I'm at it since I have to disconnect so much **** anyways.

86rxNa

That's a nice clean looking Tb!