base idle

[Tri2Tri]

Due to the idle jumping around and stalling at roundabouts ect once you lift the throttle I decided to clean the stepper motor. This had heavy sooty deposits and looked like it had never been cleaned. While the stepper motor was out I thought i would check the base idle. This is what I did, is this correct.
I blocked off the stepper motor hole in the plenum. Turned engine over which idled at 2,200 revs. I tried to adjust the idle screw on the plenum but it was screwed right down. I tok the idle screw out and cleaned up the screw and also were the screw sits. There was a lot of black sludge. I put the idle screw back in and started the engine...reved around 2,800 revs. As i screwed the idle in it took a while before this effected the revs and only the last part of the screwing in had any effect which made the idle sit back at 2,200 revs....this was with the screw fully screwed down.
I replaced the stepper motor and turned the engine over. revs settled at 900rpm.
Now this is fine but im confused as to why my base idle is so high???? Was I checking this wrong?

[carsy]

Although you blocked the stepper hole because you had it removed, it doesnt sound as though you blocked the air pipe from the front of the plenum which feeds the stepper. Its the twisty pipe that goes around and through the throttle linkage, this has to be blocked as well.

[Tri2Tri]

Ahhhh. Thanks Carsy. I will have another go tomorrow. Cheers.

[blitzracing]

Without blocking both the vacant stepper hole and the pipe you allow lots of air into the plenum as there is nothing to control it- hence the high RPM.

[Tri2Tri]

Right I'm off to have another go as no doubt messed up the base idle not knowing what i was doing in the first place. I now understand about blocking off the pipe but to re check the idle would i need to remove the stepper motor again and block up the hole or could i just disconect the wiring and leave the stepper motor in situ.

[spend]

You pull the hose off, cap the stub with a few fingers cut from rubber gloves and push the hose back on... That effectively seals air from going into the stepper housing & ensures all air goes through the AFM.

Check the throttle butterfly adjustment ~ feeler gauge on close (allen key under throttle stop on top) & that it fully opens (some adjustment on linkage near cable attachment). Then ensure throttle pot is still in limits or loosen & adjust when you have possibly shifted the butterfly & shaft (however minimal). Then you can adjust the base idle screw ~ good to wind it in & out a few times to loosen up & hopefully de-crud a bit.

The PCV feed into the trumpet base can also feed a fair bit of bypass into the plenum, so don't forget to clean those pipes before you start either ~ otherwise you can be going roud in circles...

[blitzracing]

Tri2Tri said:

Right I'm off to have another go as no doubt messed up the base idle not knowing what i was doing in the first place. I now understand about blocking off the pipe but to re check the idle would i need to remove the stepper motor again and block up the hole or could i just disconect the wiring and leave the stepper motor in situ.

Easiest thing to do is leave the stepper in place, and I do like the glove idea for a 100% air tight seal. The idle should drop to about 5-600 rpm. If its higher, screw the bypass screw in so the engine just idles, or vice a versa if it wont idle.

[Tri2Tri]

All sorted, thanks guys. Base idle would not keep engine ticking over. Re adjusted to 600rpm now running good and stable at 900rmp once stepper feed pipe is released.