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Wacky Idle and Power Steering Pressure Switch

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HI All

ON the subject of the Power Steering Pressure Switch

Having moved to an area where the summer is very hot my 1993 Deville 60 special 4.9L engine

On random basis on startup the idle would go nuts and sometimes engine dies 

No DTCs trip and OBD-I shows all looks good as to fuel trims, MAP, timing etc.

So I assumed it was the ISC and replaced it, though this issue then seemed better over some cold starts

the problem still exists but happened less. 

I assumed then it was a thermal issue as the weather went from 100 deg days to low 80s.

Used 2 different ECMs, Memcals and calibrations and both have the same issue 

Car has over 210,000 miles on it, but more about car's age that some sensors are original and get weaker.

So I started researching this, and it hit me a weak PSP can cause idle issues 

It is even labeled as part replacement as :

1993 Cadillac DeVille Idle Speed Control Power Steering Pressure Switch - 10218778 AC Delco - $24.18

I understand testing the PSP with an Ohm meter with steering wheel flat straight will show open and when wheels are locked hard either direction then circuit should then be closed

Question is having PSP not fully going faulty but having degraded cause the idle issue ?

I did a simple test where on cold start kept the wheels dead straight and idle was perfect around 650 RPMs for good 5 minutes.

The began turning steering wheel back & forth (half to full wheel to wheel) and sure enough idle RPMS change. 

Put the wheels straight, idle fine and again back/forth on steering wheel and RPMS go up and down

So where physically exactly is it for 1993 as from engine bay I could not find it ?

Is this on the rack and only can be seen/replaced jacking front end up and getting under there 

and if so, can PSP be replaced without having to take other things out ?

I assume being down there then taking PSP off that will lose most of the power steering fluid and when PSP is installed have to add fluid and then bleed the system ?

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