1994 940 w/B230FT 97k miles (original owner)

I have been trying to run down the elusive rough idle gremlin. Seems to be a popular problem discussed here. I think I have exhausted all the FAQ help.

Two weeks ago I removed the throttle body for cleaning using the FAQ instructions. The goal was to improve performance and fuel economy. Idle was a somewhat drifting 600-800 rpm. There was a significant amount of build up on the plate and body that was easily removed by a fuel injection cleaner spray and a little brushing. Put it back together and the engine ran smoother with a more steady idle at about 600-700 rpm (no adjustments needed). Ran the car for about 300 miles of normal driving with no problems.

Two days ago I decided to see if cleaning the Idle Control Valve (ICV) would further smooth the idle. I removed the throttle body since it made for easier access to the ICV. Found the same black build up in the ICV and cleaned it off with the fuel injection cleaner. Put it all back together and voila....the engine idled at 1600 rpm! Took it all apart again and looked for my mistake. Inspected for a vacuum leak, especially the ICV to manifold hose and the throttle body gasket, none to be found. Consulted the FAQ’s again Tried to adjust the idle screw and checked the Throttle Position Switch (TPS), throttle cable and linkage. Could not lower the idle below 1200 rpm. (engine warm and in park) Car will idle at 650 in drive with the brake on. If I pinch off the ICV inlet hose with my finger and thumb the idle can be forced down all the way to engine stall.

Things tried:

Pulled and inspected the throttle body, plate is fully closing and the TPS is set correctly

Pulled the ICV, tested per the FAQ: contacts read 8 ohms, applied 12 volt power and it actuates

Ran On Board Diagnostics, no fault codes (ran Test Modes 1, 2 and 3 the TPS response was correct and the ICV actuated when queued).


Did I damage the ICV by cleaning or is there something else I should look for?

Thanks for your responses in advance,

Mike