Cautionary Tale re: throttle body replacement/calibration

(Cliff's notes: if you get throttle-body related codes that suggest one or both may be failing, replace them asap and don't screw around throwing parts at the car blindly as I did, or you may fry your ECU (as I did!)).

Figured I would make a post to share some recent knowledge I've obtained in hopes that others may be able to avoid the mistakes I made and the secondary damage that can occur if you don't properly diagnose and address TB-related calibration issues. This issue has not been frequently discussed on the forums because our throttle bodies are generally reliable, and frankly, most of the cars on the forum have not yet reached mileage levels where throttle body issues are starting to manifest. For reference, my car is a 66k mile 430 scud, but I believe the same issues can afflict both 360's and f430's. I think that is why my searches for the relevant codes did not turn up much, so I wanted to make sure this post would pop up in future searches.

So here is my story. A few months ago I started getting throttle-related codes, frequently followed by the car going into limited rpm limp mode. The codes suggested a throttle pedal sensor (potentiometer) or throttle body "synchronization" issue. The codes were not always the same, but always included P2121 (throttle/pedal position sensor/switch D - Circuit Range/Performance), and later P1197 (throttle body "self learning" fault), and P0226 (Throttle/Pedal Position sensor/switch C -Circuit Range/Performance Problem) I'm no expert, but I believe the system works by throwing codes if the input signals coming to/from the pedal don't match the TB's or if the TB's are not synched up sufficiently close (because one is failing/lagging). When I would get the codes I would clear them (either through my code reader or by doing a battery reset), and the car would drive normally for a while, but the issues would return after some time.

So I started throwing parts at the car. First I got a new pedal potentiometer. That seemed to work for a while, but the codes eventually came back. After a lot of research and checking to ensure my wiring was all good, I decided that the problem was likely a lagging/failing TB causing it to fall out of the acceptable synchronization range with the other TB. I knew the dealer recommends replacing both when this happens, but that just sounded like dealer speak to me so I bought a used one in hopes that it would be in better shape than my 66k mile unit, and figured I'd start swapping it around to see if that worked. Again, it did for a while, but the codes eventually came back. So then I bought a brand new one and tried that, but again the codes returned. By this time the "self learning" code p1197 popping up so I bit the bullet and bought another new TB so I could have two brand new throttle bodies.

I was certain this would cure the problem, but it didn't. The codes came back and it eventually got to the point where the car would go into limp mode pretty much immediately. A bit of additional research revealed that new throttle bodies must be "calibrated" using a factory (or factory-like scan) tool and that a mere battery reset or "soft calibration" after a reset can accomplish (unless you get lucky I guess, and your new TB's are already pretty much perfectly in-sync). So I took the car into my trusted indy to have the calibration done, only to be surprised to learn that the self learning/throttle calibration procedure would not complete using a Leonardo. So the techs went through all the wiring, only to find everything in spec. That left only one item: the engine ecu's. I sourced some used ones (VERY pricey), and lo and behold the calibration completed immediately and the car has been perfect ever since.

More research and input (including some helpful input from Stef at Scud Ing Swiss) revealed that if you have a failing step motor in a throttle body and it is not caught soon enough, you can fry the Motronic ECU. Per Stef " the internal H-Bridge Mosfet driver of a quite old generation really doesn't like to be over-powered by a failing step motor especially when PWM is applied at its gate." I'm not sure exactly what this means, other than if you don't fix a failing tb in time you can screw up your ecu, and that is exactly what happened to me.

So, moral of the story, if you get any of these codes, unless you know for sure that you have a pedal issue that can be resolved by a new potentiometer, I would replace both TB's and then get a proper throttle body calibration done. Otherwise, a bricked ECU may be in your future. Oh well, live and learn. On the plus side, my car feels pretty great with two new TB's, a new throttle position sensor, two new MAF's, and two new 02's! Hope this helps someone!

 

You guys are all correct. And yes, I’m going to keep the ecu’s just in case. Sadly they were replacements themselves as they had 2016 date codes on them. The first replacement was necessitated when the car was jumpstarted backwards years before I got it (verified through service records) and fried both ECUs and the TCU. So I’m sure they are still good other than the burned up bridge part thingy! Been driving it like crazy last couple days. These things straight up rip.