High Idle Issue

[SpecM]

Got my five-speed swap all done about two weeks ago, very happy with that

Now my idle is almost always high. Around 800-1000, rather than the normal 600-700 rpm. The strange thing is that the idle is very steady, just high. Sometimes around 800, sometimes 1000.

I have checked for intake leaks (yes Jim I used a smoke machine!), checked the TPS idle switch, cleaned the ICV, and made sure the thottle cables and idle stop were not interfering.

any ideas? is my ICV toast?

'89 325i, stock m20, unchipped, around 200k miles

[nando]

does the ICV buzz?

800rpm would be acceptable but not 1000..

[jlevie]

Does the idle speed change when you unplug the ICV (it should rise if the ICV is working).

Is the throttle arm resting on the idle stop screw? If you force the throttle arm closed does the idle drop? A binding throttle cable can prevent the throttle from completely closing or it is possible that the idle stop screw needs to be readjusted.

[SpecM]

the ICV does indeed buzz

[SpecM]

Does the idle speed change when you unplug the ICV (it should rise if the ICV is working).

Is the throttle arm resting on the idle stop screw? If you force the throttle arm closed does the idle drop? A binding throttle cable can prevent the throttle from completely closing or it is possible that the idle stop screw needs to be readjusted.

the idle does NOT change if I unplug the ICV

I backed off the tension of the throttle cable, and the stop screw also. No change.

I just tried this: If I force the arm closed, it does return to about 600-700! Is the throttle valve worn out?

[jlevie]

Before you backed off on the idle stop screw did the idle change when you forced the throttle closed?

You could have a binding throttle body. The usual fix for that is to remove the throttle body and clean it. Once you've done that you have to check the adjustment of the idle stop screw and TPS. You will certainly have to adjust at least the idle stop screw now since you fiddled with it.

To set the idle stop, warm up the engine until it is at normal operating temperature. Disconnect the ICV and adjust the stop screw for an idle of 950rpm. Then, using a test light or ohmmeter, adjust the TPS so that the idle switch closes when the throttle stop is 0.030-0.060" off the idle stop screw. Start the engine and plug in the ICV. The idle should stabilize at 750rpm.

[SpecM]

Before you backed off on the idle stop screw did the idle change when you forced the throttle closed?

yes

[jlevie]

Okay, if you made sure that the throttle and/or cruise control cable wasn't holding the throttle open before you futzed with the idle stop screw, then the throttle is binding.

[SpecM]

then the throttle is binding.

ok... I've cleaned the hell out of the plate and bore to no avail. Is the crud built up in the shaft or linkage? Removing the throttle would help clean this out?

or do I need a new TB?

[Bene]

does the ICV buzz?

800rpm would be acceptable but not 1000..

is it supposed to?

[nando]

yes, it's a PWM valve that operates somewhere around 90hz

[SpecM]

ok... I've cleaned the hell out of the plate and bore to no avail. Is the crud built up in the shaft or linkage? Removing the throttle would help clean this out?

or do I need a new TB?

bump for Jim

[jlevie]

ok... I've cleaned the hell out of the plate and bore to no avail. Is the crud built up in the shaft or linkage? Removing the throttle would help clean this out?

or do I need a new TB?

It is going to be difficult to tell what is up with the throttle body with it on the car. Remove it, clean it and then see if it still binds. It is just possible that the TPS could be the cause of the binding, so remove it and see if the throttle still binds.