Idle speed not raising on heat or headlights

[fixkick]

I’ve got a 91 2 door with manual transmission.  The idle speed increases when I turn on the AC, but doesn’t rise when the heat is turned on, or headlights, or steering wheel is turned at idle.  This is a huge mystery to me.  I tend to use my vehicle as a mobile work light so being able to keep the battery charged at idle with lights on is super useful. Cheers!

that is because it is NOT a 89/90 car.
and you are reading the wrong manual  for 89/90 and not the correct 91.


91+ all 91s and newer only race idle speeds at AC and overload PS pump (sensor switch)
that is it.
this ended because the ISC faster and more powerful, now. 
and can hold 800 RPM perfectly under all condition motor hot normal temperature.
and they DO.
the Generator alternator no problem at all running stock lighting ever, at 800 RPM (a fact)

so my guess is your car has a  problem of somekind but I am not sure what, not stated yet.

Interesting.  That’s good to be aware of, but my idle speed does drop when any of those things are done.  Is that normal? It doesn’t hold 800 under load, other than AC. I don’t and never have had any stalling issues, so maybe everything is okay.  It seems to typically run around 600ish under load.  Also I have the 91 Geo Tracker manual which states the idle speed should rise to 920.  I’ll take that as a typo.

 
first off no car told yet is it Suzuki Sidekick or  Geo tracker. (you just said tracker)
is it G13 or G16 engine.?
is it 8v valves, ?
what is the VIN code (I  can decode that , even leave off last 6 number for the serial at end I do not need)
does not hold 800 RPM under load, no load stated, what load,? this is really odd,  there is no load with car parked,  the alternator is  600 watts max and is only using   0.8HP (10% of engine full 80HP power) and not any one thing on car uses 600watts, 120watts for head lights is nothing there.
No AC here, no AC load,  do you have some odd 1000watt light bars or some such thing, An OFF ROAD car of some kind,  no idea at all me.
again i  do know know what you mean by load.  nor what things added to any car , me here blind , with no photo or car.
a 5speed box is NO LOAD ever in NEUTRAL, zero load, so what is this load thing?

a normal hot engine never runs at 600 RPM ever,  lowest possible is 750 highest is 850 (AC off, Power steering not overloaded (lock do lock turn steering hard over forced and bingo overload heard at PS pump)

91 Geo Tracker manual  920,  that is never hot idle normal on ANY G16 ever. hot fast idle can be 920 or 1000 and really 80RPM lower is not big thing for AC on why worry 80RPM?


some manuals published maker makes  carry over errors, GM/GEO books are full of errors,  after they translated the real manuals (Suzuki) to GEO's lies sure.
the 90 year, fast idle is 920  I think but gee  wiz such  rare book that is.. super rare, now, 30 long years old, wow.

what you should ask and did not, is why 600 rpm hot, and I say is it really hot.  180F water temp,  if not the thermostat is NO GOOD.  and all EFI cars  made even 2020 the ECU EFI system will go nuts at wrong hot engine temps.

600 is DEAD WRONG and has causes.

1. engine not hot not 180f to 195F temp,  180 is stock. is it at the proper temp.?
   
2. ISC stuck,  your power steering test causes 920 to 1000pm proves it is now, stuck.
   
3. The engine can go lean, AFR air fuel ratio, fuel pressure low and engine can be so weak RPM falls to 600 parked in neutral.
   
4. the engine goes way rich , then misfires and that causes RPM to go wrong too, even 600.
   
5. Bad spark (a 60k mile tune up missed , spark parts?)
   
6. EGR sticks open RPM will fail even to 400RPM is common,
   
7. clogged Air cleaner or bad fuel.
   
8. bad MAP sensor.  or hoses to it cracked or clogged
   
9. The CEL lamp? turns on key on? it must , does it>?
   
10. start engine CEL lamp goes out ! and must does it? if not ECU is locked up in limp-home mode, and that mode ends all idle controls (random RPM ensues)
    
11. O2 sensor shorted and engine goes rich, see #4.
    
12. injector TBI leaks, see#4
    
13. FPR stuck closed , see #4
    
14. CAM belt ignored at 60kmiles service check, and now slips at 100kmiles  or less, engine power fall to below 1/2 power now, even 40 HP, or less. oops. no service.
    
15. Bad ECU,
    
16. ECT sensor stuck at 10,000 ohms not 3000 hot engine,.then it goes rich see #4
    
17. Cat melted and clogged and engine power is SUPER LOW,  and when worse never starts again..
    

does DLC jumper test show DTC code 12, the diagnostic jumper code 12 means good. does it?


BTW 1: the 800 rpm is federal EPA law here, to lower smog this is the lowest RPM allowed, and is hard coded in the the ECU brain memory ROM that code. that firmware. is hard and fast.

The AC fast idle makes the compressor work better, for sure hot days.
The PS fast idle is to prevent stalls with PS overload. at pUmp. PS

on hot engine all 3 are hard coded in firmware this RPM, 

920/1000 RPM , i never ever used m fancy optical tachometer to see it was exactly 1000 or not ever.
and dont really care, but I can tell you are are like 25 or more ECU used in 1991 in all counties and even revision onces, like 56B30  or b31, b32, and the like and never seen the me.
my 56B30  ECU was in  my 1991. 2door geo.  and never once went to 600, and if did my custom scan tool would find out why. fast.

let me explain how 600 does not happen hot.
the ECU sees RPM full time hot ever second.
and if it RPM drops due to say alternator going to 600watts load 50 amps say battery was near dead it can do that, the ECU opens the ISC valve and RPM holds at 800
this is called SERVO loop and is a firmware loop that is endless. and very predictable. (just like cruise controls are)
the only way for this to fail  is ISC has lost control and that only happens with gloss loss of engine power by any CAUSE.  or stuck in limphome mode.