355 high idle/RPM sensor

I have the same problem at the moment. If I took a guess I would say it is the crank angle sensor. Someone however told me the issue is the stepper motor or I might have a vacuum air leak causing the high idling. I am idling around 2000rpm at the moment.

 

First of all I do agree that the "manual" is frustrating to say the least. It really is a pain in the ass to try and figure out what exactly to look at when the manuals are written so poorly.

Okay.

My guess is that it's the "phase sensor", or as I call it the cam sensor. Reason being, back when I had a problem with a crank sensor the engine would misfire. But first things first. Make sure that all of your grounds are hooked up properly. Then I would have a very close look at the condition of the wiring, and cleanliness of the pins inside the connectors.

 

A high idle could be a *lot* of different things. The error code that you are getting (1121) is reporting a bad crank angle (RPM) sensor. Did you check *both* engine computers (for error codes) in your engine bay? Those RPM sensors are known for being hooked up via plasto-metal connectors that go bad or that the wiring strips out. And the crank angle sensors themselves do go bad, too. You'll want to do what it takes to remediate that error code.

That being said, Motronic 2.7 adjusts its idle fuel maps based on coolant temperature and battery voltage. A bad coolant sensor (which is a different sensor than the one which displays coolant temp inside your cockpit guage) could easily trigger a high idle. Ditto for a low battery, even if your alternator is working. Put your voltmeter leads into your cigarette lighter compartment to read your voltage with car off and at idle as a free test to eliminate that possibility.

Next, clean your MAFs! CFC MAF cleaner is the real deal. Use a full can on each MAF (the small wire elements visible inside the black open tube).

Also, clean the MAF exterior metal contacts with contact cleaner, then coat them (and the pins on the black data cable that connects to the MAF) with Stabilant 22a or other electrical contact enhancer.

If the above doesn't help your idle, then disconnect the electrical cable that goes to your idle intake air valve (do 355s have 2??). See if that lowers your idle. Replace it or clean it if that solves your problem, and reconnect that cable regardless after your test.


Likewise, verify that your floor mat isn't pressing your gas pedal (this happened to me...very embarassing) and that your throttle cable is freely moving (lube the cable with an elevated IV drip bag of WD-40 + graphite powder mixture, lube the throttle assembly mechanicals with WD-40 spray) with no rubbing/obstructions anywhere. Blip your gas pedal a couple of times to help check for sticking.

Use a rubber hose to your ear to listen for vacuum leaks (hissing) around the engine compartment.

Check for obvious air intake leaks, too (especially on the engine side of your MAFs at hose-clamp connections).

If the above still hasn't helped your idle, it may be that your individual throttle bodies need to be synched up (also consider cleaning the throttle butterflies chemically).

 

Fill your coolant!

 

Yes.

The main one you want to check is the one from the engine to the frame. On my 348 it gets attached to a gear box bolt. Not for sure where they have it hooked up for the 355? The other one is the ground running for the alternator to the frame.

No Doubt already mentioned it, you may have a screwy Idle Air Control Valve? Still check the grounds first, then ALL of the connectors, then the IACV, and finally the cam sensor. Wiring problems in these cars can be THE biggest pain in the ass.

 

Sweet find!!!!

 

Check for Vacuum Leaks if it has not been mentioned yet.