RPM Dangerous Quick Drop at > 30MPH

[Squad-G]

Hi All!

After 60 000 miles on the car, I am now facing another problem but this one is a mistery to me.

While driving the car at above 30mph, randomly, the RPM will drop from for example ~2200 to ~1500 in an instant. We can feel the car "locking" for a second.

I have recorded using Torque the trip and I uploaded the CSV file at: http://www.filedropper.com/tracklog-...anv-1316-55-22

On line 402, you can see the RPM at 2235 and line 403 it says 1618.5.

The car has been at the dealer 4 hours and they weren't able to find the problem. They cleaned the contacts, checked for ground issues but nothing. They also changed the air intake sensor and the coolant sensor saying they were off by too much. Didn't do any difference.

I changed myself the plug wire set (not the module, just the wires) but the problem remain. Spark plugs were replaced 2 years ago (15 000 miles ago).

The car isn't giving any P codes, however, while the RPM drop happen, the check engine light show up for less then a second and disappear. The dealer found DTC U0167 (ECM LOST COMM WITH IMMOBILIZER) and DTC U0401 (LOST COMM WITH ECM).

During a 15 miles trip, the problem can show up from 1 to 10 times.

If the problem occur while the cruise control is ON, it's impossible to set the cruise control again back after unless you stop and restart the car.

Please note, this is my girlfriend's car and it's actually not an Aveo but a 2008 Pontiac Wave. It's an automatic.

Thanks for any input in advance.

[Daox]

I'd look at the wiring to and/or the immobilizer. I would imagine that if the ECU lost contact with it, it will shut down the engine. That would account for the rpm drop.

[Squad-G]

I'd look at the wiring to and/or the immobilizer. I would imagine that if the ECU lost contact with it, it will shut down the engine. That would account for the rpm drop.

Thanks for your suggestion. Do you happen to know where is the immobilizer in this car?