[Supras] Help! Idle cutoff cycle

[Hacker J]

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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