ErikS500

Hope someone can give me some advice on how to diagnose and fix this issue. Recently, while driving on the highway at a steady speed, there was a sudden reduction in torque. From that point onwards the engine had about half its performance. No warning or error messages. Diagnostic machine pointed to faulty TBA (Throttle Body Actuator). however, I do not believe that, as I can still manage 160 km/h albeit with severely reduced torque and I need to keep the revs above 3000 rpm. Below that the engine has almost no torque - it is so bad that pulling away at a traffic light happens excruciatingly slowly. Only once the revs rise above 3000 rpm does the car make some progress, but then only as if it had a 2000cc engine. The cruise control still works fine, but with frequent gear down changes due to lack of torque.
I have actually removed the TBA and opened it up. The electric motor still opens the throttle fully if about 5V is applied to it, and spins freely if the gear is removed. therefore I do not believe the TBA is faulty, but I suspect the current supply from the ECU (engine control unit) is at fault. When the engine is started it behaves normally initially. A blip on the pedal instantly sends the revs up, but the second blip has a delayed and extremely sluggish response. Same with pulling away from rest after having started the car. It surges forwards and then it is as if the gas pedal is suddenly released, the car proceeds to crawl further. When I stop and restart, its this process is repeated. If I pull away VERY gently, it goes OK, but the extra torques required at the gear change causes it to fail, after which it crawls.
Measuring the voltage on the supply wires to the TBA, it shows about 6 Volt when blipping the throttle the first time, and only 2.3V thereafter. This leads me to suspect a partial failure of the output buffer transistor in the ECU. But which of the 2 dozen transistors that might be, and what the replacement part number would be, I have not been able to determine. Can somebody help?

VMAX7

I dont know but if you need a used accelerator pedal i have a couple.

S430LUCKDRAGON

The problem you describe sounds more like TCM issues to me , mine was doing all the same things and it was the transmission contact plate there is a small o ring on the harness that runs from the transmission oil pan to the TCM located in the fuse box on the front passenger side , the BCM is also in the same place the TCM is the one closest to the front of the car any ways some how the o ring leaks and the oil travels into the TCM and fries the transmission contact plate , I replaced the contact plate , just the contact plate solinoids are reusable and cleaned my TCM out with electrical cleaner that was 2 years ago amd still running fine now , to replace the contact plate the transmission oil pan and valve body have to come down you can find many articles on this on here its a common problem with these cars , there is also the bushing for the wiring harness that needs to be replaced I paid 500$ for the contact plate and 23$ for the bushing
Good luck

ErikS500

Thanks S430LUCKDRAGON for your input. although I may not quite agree with you, as the problem is there whether the car is in gear or not. But worth having a look at. Which side is passenger side? Left or right? On my car it's left. Another member suggested the pedal. Also worth looking at. On start up the engine behaves normally but as soon as torque is asked, it fails. When switching off and starting again, it is normal again.

tusabes

Interested to see what you find as the fix

I have the same no torque below 3000rpm issue

I'm inclined to think its the transmission plate as it's such a common issue

ErikS500

Hi all

Any further suggestions on this issue and what may cause it?