I've searched the forum and got the usual unusable results. 1998 550 VIN ZFFZR49A9W0111382. Idle speed is approximately 1100 RPM, hot or cold, higher as expected with AC engaged. I believe it is supposed to be 900 RPM? Searching the shop manual seems to reveal that special instrumentation (through OBD?} is required to set the idle speed. All to say, it cannot be set by simply turning a screw somewhere - correct? If so, is it possible to explain, in something close to layman's terms, what is required? Thanks much. ~Troyce
If I'm not mistaken, the 550 idles at 1100 or so, whereas the 575 is in the 900 range. I'm sure one of the more knowledgable guys will chime in with the correct numbers.
Lots of good info in the WSM on this subject. In short, no. The idle speed is set by the ECUs via the IAC motors. Bank to bank synch is a semi- involved process as outlined in the WSM.
Troyce, as David said, the WSM really does have good information on how to do this, and if you read between the lines, you don't "have" to have an SD-1 or 2, only a multimeter and the 21st century version of a Unisyn carb synchroniser, although some OBD2 software and a laptop would be very useful, too. IMO, it's more important to understand what they're doing in the procedure, than to simply follow the procedure. But before attempting the bank to bank balancing, you really need to ensure there aren't any other air leaks that could be causing the higher than normal idle. If you have an air leak elsewhere in the intake of the engine, and you attempt the balancing procedure, you'll likely wind up worse than when you started, so make sure the rest of your intake system is well sealed before you start. On the older cars, the paper gaskets between the intake manifold and heads are known leakers, so if you haven't already replaced these with the updated 575M elastomer coated metal gaskets, you should. The left/right/top plenum gaskets can also be a source of air leakage. The test for air leakage is to spray carb cleaner around the perimeter of all these gaskets, with the engine idling, and see if it speeds up. It's a crude test, and won't find very small leaks, but it's about the best a DIY'er can do.
Always start here...Fuel trim or adaptive values will be high if there are leaks. Haven't met a 550 or 456 with original plenum or intake manifold gaskets that wasn't leaking!
I don't find ferrari guages to be all that accurate. I do believe the readings I get on my obd2 reader. I use a kiwi obd2 reader bluetooth to my phone. I get lots of data one being a true rpm. I would start there 1st.
WSM says idle should be 960 without AC engaged and 1020 with AC engaged. Idle should be set to 900 with oxygen sensor and idling speed adjuster disconnected and engine at operating temp (coolant temp = 197.5F, +/- 4.5F). Sounds like your car is idling pretty close to normal.
Much thanks for all the quick replies. My extensive experience with multi-cylinder motorcycle engines should have told me to look for an intake leak - a very common problem there too. Without getting too far from the topic as well as having not even read the manual regarding the job, do most here judge the replacement of the intake and plenum gaskets to be do-able by someone with fairly decent mechanical skills?
Oftentimes, the gasket can be seen "extruded" around the #1 intake port. A squirt of BrakeKleen or CarbKleener will disrupt the idle if a leak is present. If you have the capabilities to measure fuel trim, you will see elevated values. Yes, but a helper is advised to lift the plenum off. It is modestly heavy and the car is wide. Your back will thank me later....And while you're in there, it would be the time to inspect/replace the coolant hoses in the valley.
