I have a 1997 Ruf-modified C2. Every now and then it will not return to a normal 800-ish RPM idle but hangs at 1200 to 2000. I’ve looked for the obvious things… Vacuum lines and elbows are all perfect and throttle cable as slack at the throttlebody and no obstructions. What is notable to me is that I can pinch the idle air control valve hose flat and idle returns to normal. I can *sometimes* unplug and replug that valve and get a normal idle. Before I buy a $300 part as an experiment, anybody have any ideas? THANKS!

 

Clean it?

 

Removed and inspected... Shiny as new. Moves freely with a bit of bouncy action, as new. Jetted a bit of carb cleaner just cause why not... No joy. Weird.

 

My guess is a bad contact or fault on the cylinder head temp sensor ref :- https://rennlist.com/forums/993-foru...mp-sensor.html

 

Should this be easy to verify with an OBDC reader that displays running data?
Andy

 

Hi Steve,
--With the ignition on do you feel the idle valve vibrate or hum a little? This will verify it is operating.
--Also, it may be worth checking the actuator on the front of the heater duct in the engine compartment, The internal diaphragm rips with age and leaks. It is easily checked by detaching its tube and slipping a small rubber fuel hose or fishtank-like air tube onto it and applying vacuum with your mouth to see if it holds vacuum or leaks.
--Also for a late 1995MY-on car when you press the recirculation button on the CCU do you hear a thwak and a change in air sounds behind the dash? This validates the vacuum actuator behind the CCU is working.
Andy

 

Yeah, I was thinking vacuum leak also.
on the throttle body there’s a line with a stop valve that feeds various vacuum operated parts- the “suck on a tube” method Andy describes is how I debug these. You have the resonance flap, the SAI, the EVAP and something else that escapes me on the circuit.