It's not the floor mats! I've confirmed this! Here's the weird thing - my hot running idle varies between 1,000 - 2,000 rpm. I know how to access the idle knob, but once it's set, it will still vary, all other conditions being equal. Example - just went on a 50 mile run. At lights, the idle was at 2,000 rpm, consistantly, every single light. 90 degree day, oil temp 175, water temp 190. Cut the motor, go into a store for 5 minutes, restart, and the idle is now 1,500 for the remainder of the drive. And all this is with the idle previously set to run at 1,000 when warm. Any ideas?
Since your electronic ignition system is fairly reliable (no mechanical advance mechanism to stick), you must have an intermittent air leak somewhere into the intake tract. First thing to try (when the idle is high) is to physically pinch one of the big rubber air lines on the AAV closed (i.e., simulate the AAV being fully closed as it should be during warm running). Also when you say that it's not the mats, have you confirmed the throttle plate is at the idle rest position even when the idle is high? Also, please confirm whether US or Euro version (the euro version 328 has a gizmo that could be involved).
My recent post.......... Okay Luigi.... I know your car is rather different now but I had a similar problem with my 328. The fast idle seemed kind of random. I mean the engine could be fully warmed up, I shut it off for only a minute or two and when I restart I get high idle again (around 1500 rpm). Would also happen at a stop light when I take it out of gear etc. I verified that the aux. air valve worked properly when heated and cooled and I did not find any vacuum leaks on the engine. Recently I removed the coolant bridge (in the photo) that connects the two coolant manifolds from the heads. I found that the small pipe, on the bridge, that runs to the coolant expansion tank was plugged up with "gunk." I would say it was at least 50% blocked. The rest of the cooling system looked very clean. For some reason, probably the small tube diameter, it likes to collect in there. Anyway, this tube allows coolant to circulate through the expansion tank. The coolant continually goes in and out of the tank and this means the coolant temperature in the tank should be more or less representative of the coolant temperature in the block. This is important because the aux. air valve is mounted to the bottom of the coolant tank and the water temperature in the tank dictates how much the air valve closes (reducing idle). Now.... if the small tube going to the expansion tank is not passing as much water as when it was new (because of the blockage) the average temperature in the expansion tank will probably be lower (colder) than it should be in comparison the majority of the coolant in the block. If the tank temperature is abnormally low because of poor circulation the aux. air valve will be open to a greater degree, resulting in a higher idle, because it "thinks" the engine is cold (or colder than it really is). Unfortunately I cannot verifty that cleaning this coolant bridge tube on my car solved the problem because I have removed the aux. air valve, vacuum valve, cold start injector etc. from my car along with other parts. I'm hoping these parts are not essential but I will not know until I finish the major + on my car and see how it starts/runs. Also, I know there are some variations between models. I don't have a temp. switch on my coolant tank, a lambda sensor, frequency valve etc. Erich
Also check Luigi's thread 'wierd fast idle on 308QV' further down the Technical Q & A's, he points out a vacumn leak problem, have not checked my lines yet.
Also check the butterfly is closing properly on the throttle body - they get pretty dirty & can get gummed up such that the dirt is holding the butterfly open slightly. Not difficult to remove & clean. Just actuate the throttle mechanism on the side of the TB by hand (with the engine off) & see what it does. you should see/hear the butterfly closing positively. When you let go of it, if you can then push it a little further closed then it probably needs a good clean. My money's also on a vacuum leak though to be honest! I.
