I've done tons of searching and reading of previous posts, but any insight you guys/gals can provide would be appreciated.

The idle speed on my 1987 240DL sometimes increases for no apparent reason, and sometimes the car is really difficult to start when hot, but after it cools down, starts right up.

I gave the car a tune up (plugs, distributor cap, rotor) and cleaned the throttle body with the ipd kit. When I had the throttle body off, I checked the throttle position switch - I hear the faintest of clicks, but the click doesn't happen until the throttle is maybe 1/8 to 1/4 open. I was careful not to soak the tps with cleaner, but when I rotated the butterfly valve, the tps sounded a little gritty. I also did not clean specifically the knurled idle speed knob at the time. The idle speed control valve has not been touched, but the throttle plate and body was pretty dirty.

Questions:
I am thinking the problem is probably the throttle position switch. How loud should the click be? It was so faint as to be barely audible - is that normal? Is there a way to electronically check the tps to make sure it is working with a multi-meter before I buy a replacement?

What about the idle air control valve? Is this something that can or should be cleaned with throttle body cleaner? It's nearly a $200 part and I hate to just throw money at the problem, but then again, part of me says to replace all the normal wear items in the ignition and fuel intake.

- The fuel pump was replaced a year ago
- The mileage on the car is around 160k miles
- Flame Trap relocation kit recently installed (old flame trap was not clogged)