FWIW, in case this can be useful to someone. I bring the shark for yearly service, take the car back after a few hours, everything's fine. Seems btw that the car did not need a replacement of the ball joint of the front stabilizing bar, this stealth TSB issued last summer which seems to affect only a handful of 550s. I take the car back, everything feels and sounds fine, drive the car to the work, 60 miles later the car is idling at around 1600-1800rpm when warm. Driving back home, same thing, 1600+ rpm idling, very annoying. Rang the dealership on saturday, trying to find a mechanic who eventually called me back and told me to: - disconnect the battery switch for a minute or two - reconnect and wait 2 minutes - start the car and let it idle for a minute and then go for a drive. Obviously, this is about a sensor/ECU related function taking a new reference after having been reset, but since the 550 has a good old mechanical throttle, I am not sure what kind of sensor can be involved in messing up the idle rpms. Anyhow, the trick worked.
What is the spec'd idle rpm range for a 550 ? Searched the manual and this board but could not find it. My car now idles at 1200 rpm and "coasts" down to that level instead of falling down. Any idea what could be wrong/to check ?
Idle is not 1200, I have book but not right now. More like 1000-1100 I'd say. Check Inlet manifold bolts... all over... head joints, and all 3 plenums. This can be done with 1/4 drive 10mm universal jointed socket and extensions without removing anything, although it is tricky. There's rubber seals at the back over around the variable length system shafts, and they may be leaking, otherwise it's just paper gaskets. They DO come loose.
Air leak on mine has only caused high speed detonation, not erratic idle. I would depend on the size of the leak though, I assume.
Just to clarify: idle is not erratic, it's very stable, but at 1200rpm, which sounds high. When slowing down, it almost feels that there is a hint of trailing throttle. At what rpm does your car idle ?
My 2000 550 idles at around 1,000 - 1,100 ..... never experienced this problem but glad you made us aware of this. What's the scoop of the TSB you mentioned ? Years?
Look for freeplay in the primary throttle cable. There is also a possibility that the secondary cable to the passengers side throttle is maladjusted. To correct that one you would need a manometer. Take it back and let them fix it. The motor will correct for air leaks. I have seen massive air leaks in 550's from blown out manifold gaskets and the only symptoms were check engine lights for Lambda sensor out of range.
Idle may be just a little high. When cold, mine has always idled about 1100- never been a problem. I'd not sweat it.
You should read the throttle angles when synchronising 550 throttles bank to bank. The SD1 is best for this, but you can also use multimeters.
