[Supras] Help! Idle cutoff cycle

[berniek at technicaldevelop.com]

Jon:

    Thanks for the info.  I know there is a cleaning procedue for the ISC,
and a procedure for testing it by briefly energizing each winding.  Seems
odd, though, that it should happen in 100K miles.  I can also check drive to
the ISC with an oscilloscope, but your thought about it being gummed up is
probably correct.

    Take care.

        Bernie
----- Original Message ----- 
From: "Hacker J" <jonbhacker at yahoo.com>
To: <supras at supras.com>; <berniek at technicaldevelop.com>
Sent: Thursday, June 28, 2007 4:49 PM
Subject: Re: Help! Idle cutoff cycle


>
> There are no codes for the ISC. Its a stepper motor driven pintle valve.
When you shut the car off the ECU homes it back to wide open, you should be
able to hear it. Often the pintle gets gummed up.  Try cleaning it first.
>
> The surge is probably because with the ISC full open you are revving above
1600rpm with a hot engine. This engages the trailing throttle fuel cut.  The
ECU will cut the fuel back on when it hits 1200rpm.
>
> Easiest way to confirm is to disconnect the TPS connector. This will open
the IDLE switch and the ECU will not actuate the fuel cut. More details
here.
>
>
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=125
>
> Jon
> 90T
>
>
>
> ----- Original Message ----
>
>
>
> Don, Joe, Bob and and group:
>
>     I wrote before about a hunting idle condition in a '91 turbo between
800 and 100 RPM.  I have not had the time to dig into it more yet, but it
appears to be the ISc, but no codes are set.  I was going to manually
"throttle" feed to the ISC from the accordian hose by inserting a piece of
soft Tygon tubing in series with the tubiing to the ISC and then pinching it
with pliers as a test.  After tubing insertion, the flow resistance was
enough to bring the hot idle down to about 1000 RPM.  It does droop when the
A/C or lights are turned on, so apparently the ISC is not working.  But the
mystery is that no codes are set.
>
>     Anyone have any ideas?  I'm going to try to get through NJ inspection
on Thursday with it as it is.  There are hints of a BHG:  Misfire after
startup and pushing water out of the radiator.  But I intended to change the
HG next week any way.  No sign of antifreeze in the oil.
>
>         BernieK
>
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