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Discussion Starter · #1 · (Edited)
I recently resolved an issue with my 2007 XC90 V8 Sport which I thought I'd share in case anyone has something similar. It was tricky to identify and there was nothing on the web/forums I could find which were anywhere near similar.

Symptoms:
  • Engine stumbles/lurches at gear shifts (1->2 and 2->3 mostly)
  • Sometimes engine stalls at gear shift or when slowing to stop. Usually restarts quickly, but sometimes needed to crank for several seconds to restart.
  • ECM triggers camshaft codes (P0366, P0346, P0341, P0391, P0345, P0365, P0340, P0390) which are basically all 4 camshaft sensors (P036600, P036500, P034500, P034600, P039100, P034100, P034000, P039000)
  • TCM triggers a code for torque converter clutch solenoid circuit intermittent (P0744, or P074400)
  • ECM triggers a code (P061A62) which signals a fault in ECM's calculation of engine torque (Internal Control Module Torque Performance - Algorithm Based Failure)
  • ECM stored code of P2173 or P217300 - High airflow
  • Problem was temperature sensitive. When ambient temps were very cold, problem was present. When ambient temps warmed up, the problem 'almost' disappeared. Engine temperature did not seem to matter.

When I say the engine stumbled or lurched, I mean it really LURCHED. Even with recently new engine mounts, it felt like the engine might jump right out the hood. The only way to recover was to back off the throttle entirely and slowly re-apply throttle.

I have a Vida/DICE so I was doing my own diagnostics. With all the symptoms and codes, it was hard determining if the transmission or the engine was causing the bucking and lurching since the problem usually exposed itself near gear shifts. Finally after a lot of data logging with the DICE, I was able to determine the problem wasn't correlated with solenoid activation or even gear shifts. The gear shift was a coincidence, not a cause. I began to worry about the ECM's health...

Continued diagnostics with the DICE, I monitored the RPM, MAF airflow, TPS sensor 1, TPS sensor 2, and the commanded throttle position from the ECM. Turns out that at certain throttle angles, when the commanded throttle would reduce or increase very slightly, both TPS readings would sharply increase or decrease at the same time (and the airflow would increase/decrease to match). Eventually figured out that the ETM wasn't properly maintaining the actual throttle angle that the ECM was commanding.

I removed the throttle body and drilled out the rivets on the ETM cover. Inspecting the interior, I found nothing. While the symptoms are similar to the older ETM's of yore, the V8's ETM TPS is entirely non-contact with hall sensors. I did find that if I moved the throttle butterfly back and forth quickly, I'd sometimes feel a "catch" as if something was binding. Removing the actual servo motor, I found a lot of play in the rear bearing of the servo motor. I lubed up the bearing and reinstalled and the problem was entirely resolved.

Due to the significant driveability impact, I'm not going to trust the temporary fix. I'll be replacing the ETM. Factory new is over $500 (ouch).....found a low mileage one on Ebay which is on the way. Fortunately, the ETM on the V8 does not require any software downloads so at least I don't need to visit the dealer.

Hope this helps someone in the future save themselves from a significant dealership diagnostic bill (along with thousands in swapped parts while troubleshooting).
 
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