2001 - Idle jumps if I turn the wheel while stopped

Looking for some advice for my 2001 Windstar. The van recently developed a surging idle. I replaced the IAC and some vacuum lines that where questionable. This seemed to help, but only for about a day. Now, when idling, the van jumps from 700 RPM to 1500 RPM when I turn the wheel (just enough to engage the PS pump).
I upgraded the isolator bolts a few years ago, but decided to check them out again. While I was at it, I replaced the lower intake manifold gaskets, EGR valve, thermostat, air filter, coil pack, plugs and wires. I also cleaned the MAF sensor, and throttle body. Now the surging idle is gone, but the RPMs still jump when turning the wheel. It is getting dangerous to back into a parking spot, or turn while waiting for traffic.
Could this be the IMRC, or IMRC shafts leaking at the intake manifold? MAF sensor? Vacuum line to the brake booster? Any help would be much appreciated.

Regards,

Could this be the power steering pump pressure switch? I replaced the power steering pump and a low pressure line a few months ago. I used power steering fluid, not ATF...
I will check voltages at the switch this week. I will also try to bleed any residual air from the system.
I found an old post from 2006 that sounds like someone had the same problem. They never posted the resolution.

Try disconnecting that switch to see what happens.

I disconnected the switch, and the surging stopped. Now there is slight surging idle again. Much less than previously, but still noticeable (700-800 RPM). It is intermittent (a series of three or four surges with about 5-10 seconds in between series). Much more tolerable than before, though.
I will replace the switch later this week, and see if the slight surge disappears.

I suspect some sensor that feeds "engine speed" back to the PCM may be failing ... crankshaft sensor? ... tranny turbine sensor? ...??

I would say that maybe and since you disconnected the steering pressure , the PCM is going through a failsafe configuration allowing it to run (and remain running) when the steering wheel is being turned.

Probably the replacement of that sensor will definitely fix your problems.

Oscar.

Well I haven't gotten around to replacing the power steering switch yet, but the van seems to be running ok...other than the following issue:

Driving with foot on the gas at 45 mph - RPMs = 2500.
Let off the gas.
Engine holds at 2500 RPM for a about 3-5 seconds.
RPMs drop off to idle, quickly.

This happens at all speeds above idle, but is very noticable when coming to a stop light, as the RPMs will drop off suddenly. The van never stalls, but this has been slowly getting worse since disconnecting the power steering switch.
Is this a bad/failing TPS (or other sensor - 12ounce) or a result of the ps switch being disconnected?

Is this a bad/failing TPS

Would be the first suspect on the list.

The IAC would also be suspect.
The IAC is what controls the idle speed (controlled by the PCM) when your foot is not on the accellerator.
You cleaned it already......so maybe it needs replaced?

When I cleaned the IAC on my Windstar.....I removed the 2 small bolts that secure it....unplug the electrical connection.....THEN, I hold it so that the fluid I spray in will run out....and I spray Seafoam "Deep Creep" (which is the spray version) or even WD-40 into the opening in the IAC.
The fluid runs out.....taking any dirt with it and an oily film is left behind to lubricate the screw.
The IAC has a motor that drives a threaded screw........cleaning and lubrication of the threads on the screw will enable it to work smoothly.
If not....then a new IAC is in order.

It sounds like your issue is NOT just the power steering as you have idle issues in other situations.
If this is ONLY happening when your foot is NOT on the accellerator, the IAC is what comes to my mind first.

As a side note......in spite of AlldataDIY showing a power steering pressure switch....my '96 windstar did NOT have one....and at least 1 other member here also found the same issue when I told them to check this part........so the power steering pressure switch is not present on all years.......as mentioned by the OP.....they have one....but it is not always there.

Disconnecting any sensor form the engine will make the PCM use the default values stored int he memory for different situations. The behavior you mention with the RPM's staying at 2500 and going back to idle after letting of the gas is the same I've seen whenever I disconnect either the MAF, TPS, etc. maybe the steering pressure switch causes the same?.

As a side note, my windstar would also have some erratic idling when turning the wheels while in gear. I was thinking of a problem with the steering system too but turned out to be the spark plugs. I'm not saying yours might be the same, but to keep open to the possibility of other problems.

Oscar.