lower idle

[schrocketeer]

My engine idle speed has lowered over the last few months, enough so that I have to keep the "choke" lever on at least half, all of the time. If not, it almost won't stay running.
This is after it warms up, and it doesn't matter if the outside temperature is 30 or 80 degF. It runs smoothly throughout the RPM range.
Last weekend I sprayed carb cleaner around the throttle valve boots, and the return line back in to the airbox, with no change in engine speed.
I always run 90+ octane fuel. Varying gas stations doesn't change the issue. Running 93 octane with 10% ethanol, or 90 octane with no ethanol, doesn't make a difference.
Understand the "choke" lever just raises the idle speed.

[Laitch]

Are the caps on the throttle body vacuum ports in good shape?

[Martin]

With the idle set at 1000-1100 RPM press the green starter button and post the results. Any lower than 1000RPM the starter will engage. Pre 16v bricks had a inbuilt diagnostic feature to check the mixture. If everything is OK the revs should remain the same or rise very slightly if they rise significantly the mixture is lean if the revs drop it's too lean.
Regards Martin.

[stokester]

Have you checked your valve clearances? 

[billday]

How about adjusting your idle speed?

[The Mighty Gryphon]

Take the idle air screws out and check the o-rings on them.  While they're out, blow some carb cleaner through their holes.  Then blow some compressed air through them if you have it.

If that doesn't work, you might have to remove the air box to get at the MAF and clean out the idle bypass passage.  I just cleaned out a spider nest from the bypass in my spare MAF. 

[TX brick]

Have you checked your valve clearances?

Tight exhaust valves caused low idle speed on my 91 75RT.