[Supras] ISC non-operation

[Christian, Skip]

Jim,

	I'm glad your new ISC fixed your problem !!  My new one made no
difference and is still in its box in my basement :-)  Maybe there's a
difference (with the idle control) with the turbos that I'm not aware of
?
	N/A distributor had two pickups.  One is for normal operation
and one is for cold operation and is 10 degrees advanced.  Does the
turbo cam sensor have a pickup inside it (or two) ??  If it does, maybe
the operation is the same.  	Sorry, I'm just not that familiar with
the turbos.  Only have driven one & didn't like it (it was stock).  Not
enough extra power to make up for the loss of engine smoothness.  My N/A
engine feels like a BMW six in smoothness all the way to redline (that
is, when it used to run :-).
	For the head removal, I just follow the shop manual.  That way I
don't end up pulling on the head and cussing because it won't come off,
only to find I missed a bolt or two....
	Tell me about your block lapping tool & how you do it.  Also,
how long does it take ???  My block deck is a war zone (with lots of
trenches)...

Skip

-----Original Message-----
From: Jim Jobe [mailto:jjobe2 at supratech.org] 
Sent: Sunday, July 01, 2007 22:49
To: berniek at technicaldevelop.com
Cc: Christian, Skip; Supras at supras.com
Subject: Re: [Supras] ISC non-operation


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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