Ferrari 456 GT - High Idle after WOT run

Hey guys, I have a 1997 456 GT (6 speed, 5.2 Motronic) and I have a weird one that I'm hoping someone has some insight on. A couple weeks ago, I was driving *spiritedly* and all of a sudden, the engine power cut out a bit (almost like the car went into 'Limp home mode'). No CEL but I pulled over and engine idle was much higher than normal, right at 2,000RPM.

Luckily, I was near my house, so I drove it back with the high idle and let her cool down. Once cooled down, the car returned to running perfectly.

I figured it was due to one (or both) of the Idle air controllers going out so I bought brand new Bosch units and installed them...then took the car out again, and same thing! Once water and oil temps were fully warmed, I took a run at WOT and the car did the same thing: cut power (like going into limp home mode) and the high idle at 2,000RPM until she cooled down, now she runs perfectly...I just can't go WOT...in my Ferrari!

Anyway, when I got home, I hooked up my scanner tool and got the following pending codes (not stored so no CEL):

P1514 - Unknown Diagnostic Code
P0336 - Crankshaft Position Sensor "A" Circuit Range/Performance
P0103 - Mass or Volume Air Flow "A" Circuit High
P0507 - Idle Air Control System RPM Higher Than Expected

I'm wondering if the car isn't getting enough air through the intakes during the WOT runs and goes into a safety mode, high idle mode? Any insight would be greatly appreciated!

 

Thanks, Dave! That helps in regards to the 1514 code explanation. I'm pretty sure the 456 does have the "Intake manifold changeover valve" that VWs have so I'm wondering what that would be referring to. Definitely something with the air take system.

 

Yeah good questions. My guess would be high voltage. Either way, I'm going to clean the MAF connectors and make sure the female alligator clamps are nice and tight.

In regards to the battery/alternator, that's where my mind went but I recently replaced the alternator and have the car on a trickle charger when not driven for any length of time so my guess is something to do with a sensor of some kind. I'm going to look at the MAF and Throttle body position sensors and ensure they're in good working order. Will report back after I do!

 

Update: So yesterday, the car started to get the 2k RPM idle without any WOT runs! I decided to take it out and drive nice and easy. The car ended up idling for about 15 minutes while I talked to a friend and the idle suddenly jumped up.

I then took the car home and back-probed the passenger side throttle position sensor and was getting .47 volts (normal is half a volt so pretty close there). While I was working, I noticed both sides of the passenger side (Bank 1) header 2 (both where it meets the block and also where it meet the Cat) was RED HOT, like glowing! Checked the drivers side and not the case, the drivers side headers were not glowing. I got out my laser thermometer and got these numbers:

Passenger side header = 520 degrees F (Ave)
Drivers side header = 380 degrees F (Ave)

So now, I believe it's a heat issue causing the idle air controller to get too hot and go wonky. I'm sure the heat is going to cause other issues with the cooling system being on the passenger side too so I want to fix this. What would cause the header to get so hot on one bank? Timing I'm sure, but the car runs perfectly so I don't think I have a timing issue. The fuel trims are a bit on the rich side (-5 to -7% on ave) so I don't think fuel/air is the issue. Maybe the Cat is going? I don't feel the exhaust being restricted while driving and no 'slow down' light either....any recommendations guys?

 

That crossed my mind as well but my scan tool shows all four of the O2 voltages isolating normally during the weird idling...I'll be checking again to verify though.

 

As best I can discern, the Idle air controllers were getting heat soaked from the headers of the car getting so hot! I installed a heat shield which seemed to help. I haven't had the problem since but haven't driven the car as much as I'd like so I'll report back after driving some more.

I'd suggest taking a look at your headers (with a laser thermometer if possible) after a 'spirited' drive. If well over 500 F, that might be your issue too.

 

Yes, you're right they do run pretty hot. I've gotten a before temp but not after...haven't been able to go for a drive yet.

 

Just an update to close the loop on this. With the cats cleaned and the heat shield installed, I haven’t had any high idle issues for a few months now. So it seems the IACs we’re getting a bit heat soaked before doing this.

Anyway, she’s running beautifully, thanks for all your input guys!

 

Hi Juan.

Is it happening at any time or only after you 456 is warm? If it’s happening during cold starts, I’d say switching out the idle air regs for new ones would probably solve it.
BUT, I also bought 2 new idle air regs thinking that would solve it and it didn’t. It ended up being the exhaust headers heat soaking the idle air reg on bank 1. So after cleaning the cat and installing a heat shield (above the headers, below the HT leads and air intake), the issue is gone. Here’s the heat shield I ordered from Amazon:

Heatshield Products 120614 Inferno Shield 6" x 14" Stainless Heat Shield https://www.amazon.com/dp/B002UPOX9M/ref=cm_sw_r_cp_api_glc_i_q9AbGbFZVAX2N?_encoding=UTF8&psc=1

I would say order two of these (one for each side) and try this first and if it doesn’t fix your issue, keep or return to Amazon and order some new idle air regs for both sides. Hope this helps!

 

1300 seems high to me as well. Mine idles right around 950rpm which seems right to me but i guess each car is a bit different. Yes, you can adjust the idle at the throttle bodies. There's a tiny set screw that you can loosen/tighten to increase/decrease the idle speed.

I'd say try it while the car is running because you'll want to do the same adjustments to both throttle bodies to keep them in sync.

Hope that helps!