Anyone want to take a stab at this one?

I had a tear in the left intake boot and a bit of a hunting, unstable idle when in gear, but normal RPM range (550-650 rpm). In the process of replacing the intake boots, I thought I'd do something good for my car. So, I removed the throttle bodies and cleaned the caked on gunk off of them. Replaced the gaskets between the throttle bodies and intake plenum, too. Took almost 2 hrs just to scrape off the old gasket material, which had practically fused to the plenum. Reinstalled the throttles and did the throttle rest position reset procedure: key on for at least 1 minute and then off for at least 10 seconds, then start.

Now, I've got an unpredictable, high, and sometimes unstable idle issue when out of gear. In gear, it'll drop to around 750-800 rpm (still high) but stable. Take it out of gear, and it'll pop up to anywhere from 1000-1250 or so, and sometimes it will surge very rhythmically between 1000 and 1500 rpm, cutting out always right at 1500 rpm. The cutting out is sudden and misfire-like, as if the ECU suddenly recognized the runaway engine and cut ignition or fuel. It's not a sine wave like pattern. It's like a ramp wave with a sudden drop in rpm, then it will pick up again and rise over a few seconds back to 1500 and cut out.

It has now given an ESP fault a few times and gone into limp-home mode. It never once did this before I messed with it. Shutting down and restarting has always cleared the ESP fault. I'm getting fault codes P1580 (throttle actuator) and P0507 (idle). Duh!

So, any comments. Wiring? Did screwing with the connectors damage wires? As far as I can see, engine compartment wiring looks to be in good condition. Vacuum leaks? Nothing obvious. I have disconnected vacuum lines to purposefully introduce a large vacuum leak, and all that does is produce a rough running idle. Reconnect, and the idle smooths and remains high. I do have a concern over the PCV connection hidden at the back of the engine. The PCV tubes connect to the throttle bodies and wrap around to a connection in the center rear to a tube coming from the area of the front center of the engine between the cylinder banks. The tube to the right side throttle body (bank 2 throttle), seemed kind of floppy, like the connection behind the engine wasn't solid. But, I have yet to get a good look at this. That's a task for this weekend.

My only thought, is that in manhandling the throttle butterflies to clean the butterflies and the air passage, I may have damaged the potentiometers inside the actuator. I did a lot of forcible opening and closing of the butterfly. Possible? Is it that delicate? According to what I read about the P1580 code, it appears that the ECU compares the voltages from the two potentiometer circuits in the throttle body and it also compares the degree of throttle opening indicated by the potentiometer values to the throttle position sensor input and the measured air flow to determine plausibility of the throttle body pot readings. It seems to point to bad throttle body pots.

Thanks for any replies,
Brett

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1997 S600 sedan