1G Idle adjustment

[91las]

Vehicle is gen 1 n/a. Cannot get my idle down. BISS is fully down and 900-1000rpm. All necessary adjustments made (per all data) in this order:
Throttle closed switch (adjusted until feel it touch then 15/16 turn in).
TPS at 0.5v (watching through dlc/scanner)
Timing at 5 degrees with R/Y jumper grounded.
Idle adjusted with jumper grounded-black/white on firewall.
Still cannot get idle down. Prior to this my plugs showed signs of a lean condition. Vehicle does burn a slight amount of oil. Compression test dry=159, 168, 160, 178. Compression test wet=210, 190, 203, 205.

Am I missing something? Perhaps the throttle closed switch is too far in?
VERY MUCH THANKS IN ADVANCE!!

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[Pjj]

do a boost leak test to make sure you have 0 air leaks

 

[dwb]

Could be one or multiple of the following:
Vacuum leak, failing ISC, ECU capacitor leakage (causing failure in idle circuit), idle switch malfunctioning (failed, disconnected, or no ground).

 

[91las]

do a boost leak test to make sure you have 0 air leaks

Naturally aspirated.

 

[91las]

BTW, performed BG top end cleaning. Checked all windings in ISC (may need to check again). ECU was gone through last year due to injector caps leaking.
I’m pretty on top of this one for maintenance and what not. Did do a auto to man conversion, but this was quite some time ago.

 

[steve]

Naturally aspirated.

It's called a boost leak test but it's really a check for any and all vacuum leaks which applies to NA as well as turbo cars.

Fast idle is usually caused by too much air getting past the closed butterfly. Did it do this before you mucked with the IPS? Factory says don't touch it but describes how to adjust if someone has. I've found setting it as described leaves it too far open and difficult to get a good idle.

Other common causes are a bad FIAV, leaking EGR, leaking PCV, Missing throttle body ground strap, blown ISC drivers.

 

[DSMPT]

Naturally aspirated.

Doesn't matter if N/A. You have to look for is vacuum leak.
When you can't make the engine speed lower by turning the BISS down, it means the engine is sucking the air from somewhere. Which means mostly the throttle plate is open more than it should or you have vacuum leak (Somewhere between the throttle body and cylinder head inlet ports)

 

[91las]

Sounds like I need to get it to the shop and do a smoke test. This has been happening for a bit…just checked plugs and swapped out. Old plugs were white which tells me a lean condition. O2 seems to oscillate good. Performed BG top end cleaning with BG44k to the tank about 2 months ago

 

[steve]

Old plugs were white which tells me a lean condition. O2 seems to oscillate good.

I'm not so sure that the color is quite as valid with cars that run in closed loop. I don't think I've ever pulled plugs from my DSM that weren't pretty white. I think that's do to the ECU dithering the AFR to run in closed loop and that the plugs are on the hot end of their heat range and do a good job of burning off any deposits. But I haven't seen your plugs and NA and Turbo cars see different conditions so my experiences don't truly relate to yours.

If you have a post MAF air leak you wouldn't be measuring that air and that would cause you to run leaner but with your O2s switching the ECU is dealing with it when idling and cruising.

 

[91las]

do a boost leak test to make sure you have 0 air leaks

So I got my timing, base idle and all that jazz dialed in…then fine tuned. Have my tps at the lower end of the limit at .48v
Ran a smoke test this morning and it seems to be excessivly leaking through the butterfly valve. I do realize some smoke will release from certain points. But does this seem excessive?

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[steve]

But does this seem excessive?

Yes. Time to replace the seals.