[Supras] ISC non-operation

[Jim Jobe]

I've had the same problem with an ISC that ohm'ed out at 40.  I believe
spec is max 35ohm?  Swapping ISC's fixed the problem.  Sucked because
that was AFTER I traced out the wiring (7MGTE mk2 transplant).

On Sat, Jun 30, 2007 at 11:55:57PM -0400, berniek at technicaldevelop.com wrote:
> Skip and group:
> 
>     Resistance of the ISC on the '91 turbo checks fine at about 40 ohms 
> per coil (each is center tapped).  I have another one here as a spare 
> which I took apart and found relatively clean inside, and very well made 
> with sealed ball bearings supporting each side of the permanent magnet 
> armature.  I, too, doubt if the problem is the ISC proper  Nonetheless, 
> on my '90 turbo, it reduced the idle from about 1200 RPM cold to about 
> 700 hot, and also compensated for use of lights, A/C, and such.  So the 
> turbo apparently differs from the N/A in that respect. 
> 
>     However, all of the excess airflow comes through the ISC, determined 
> with a piece of small bore Tygon tubing in series with the line from the 
> accordion hose to the ISC.  Next week the salt mine is closed, so I want 
> to put in a metal HG, 550cc injectors, Lexus AFM, 57 trim turbo, HKS 
> exhaust etc.  The Walbro will follow shortly.  All of this means I had 
> better get the car inspected here in NJ on Monday morning, before 
> starting work.  So I used a short piece of Tygon tubing and a clamp 
> arrangement to get the idle speed down.
> 
>     Right now it looks as if the simplest way to get the cylinder head 
> off is to unbolt the upper intake, wire it back to the left inner 
> fender, disconnect the precat at the elbow, turbo oil and water lines, 
> and remove the head, exhaust manifold and turbo as a unit (other details 
> omitted).  I have another head ready to go from an unfinished JDM 
> rebuild, and have a 10" round lapping plate I'm adapting to a low speed 
> DC gearhead motor for block lapping. 
> 
>     Access to the ISC will be easy when the intake manifold is pulled 
> back and/or the head is off.  I have the feeling, though, that something 
> else may be amiss as you had stated.  No codes are set, but I understand 
> from Jon (HackerJ) that none are expected to be set.  Seem strange, 
> though that idle RPM grossly in error is not flagged by the ECU.    
> After reassembly, out will come the oscilloscope with a sharp insulation 
> piercing probe.  Luckily I have a couple of spare ECUs.  At one time I 
> was going to replacing the injector drivers (8 amp NEC TO-220 
> Darlingtons) with logic level FETS for lower voltage drop, so a spare 
> ECU or two was in order.  The objective was to try running the stock 
> injectors at 58 PSI to match what 550cc parts would do regarding flow, 
> but I bought as set of 550 ND injectors from Chris Hommes instead. 
> 
>        Any and all comments, especially about head removal as stated 
> above would be appreciated.  Thanks.
> 
>           BernieK
> -------------------------------------------------------------------------
> 
> 
> 
> 
> Skip Christian wrote:
> 
> Bernie/All,
> 
> 	I disconnected the ISC valve on mine - no difference.  Even
> tried opening & closing it all the way to see if the computer would
> immediately return it to where it should be for idle - it didn't.
> Finally replaced it - no difference.  If disconnecting the ISC doesn't
> help, its not the ISC (idle speed control valve).  I do not think the
> valve can respond quickly enough or far enough to cause the problem you
> have.  Computer seems to be able only to open or close it one or two
> steps, which only changes RPM by about 200-300 (if that much).  Its
> there to fine tune the idle speed, at least on the N/As.  The valve, on
> N/As does not step up the idle when the engine is cold.  On N/As, this
> is handled by an increase in ignition advance of about 10 degrees.
> 	Really recommend you remove/disconnect any fuel related mods
> that are functional at idle speed.  After disconnecting each one, cut
> power to the computer to clear the memory, then start car and take it
> out for, at least, a 15 minute drive to build up some data in the
> computer.  Then check the idle.
> 	Does your's do the same thing (or similar thing) when the engine
> is cold ??  Mine did.
> 	What mods do you have ???  This is the key (or there would be
> more cases of this problem).  Dealer didn't have a clue as to the cause
> - I asked the lead (most senior) service person.
> Good Luck, Skip
> P.S.  I only have E-Mail at work, so I'll be gone from around 2:30 today
> until 7:00 Mon.  Sorry, for the rambling, I'm an engineer.........
> 
> 
> 
> 
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