Oldblue

The P0068 could start the snowball effect.

https://www.obd-codes.com/p0068

I would read the causes and possible solutions, check the wiring and hose to the MAP

skysailor

Oldblue: Will do! Thanks.

RJ_RS_SS_350

I had a P0101, a new air filter solved the problem. Air filter is listed as a possible cause of the P0068 also.

skysailor

Thanks, that's the first thing I did when this problem surfaced :)

skysailor

Update: Have turned the car over to a local technician who has all the bells and whistles computer to diagnose the engine issues. He has so far found the aftermarket MAF that I installed was causing an incorrect temperature signal and replaced it with OEM MAF but that did not cure the overall problem. He has determined the repeating fault occurs only during the open loop phase of the system operation. As soon as it goes into closed loop all is good. Furthermore he found the problem has to do with the intake VVT but the VVT itself is fine. But if he removes the wiring connector from the intake VVT the startup is normal. Obviously can't operate that way...CEL comes on etc. So he's in the process of contacting GM to get more specific parameters relating to the signal being sent to the VVT during open loop operation. By the way, although it looks like the ECM being the culprit one of the things I have already done is to swap the ECM with a new/refurbished unit coded to my VIN and the problem remained the same. So I returned the unit for a full refund. So the technician who is as intrigued by the problem as I am has another vehicle coming into his shop with the same engine that has no problems which he will be able to do some pinout and voltage comparisons on while waiting for GM to respond. Just thought I would keep this thread alive and hope to be able to report a definitive solution to this weird problem soon! :)

donbrew

Do you understand what "open loop" means?

It means the computer is using it's own programmed tables to run the motor. ignoring input from sensors.
Open loop is only active until the O2 sensors warm up. 2-4 minutes.
Have you looked at the O2 aensors?

Oldblue

Seems a good throttle body cleaning and a MAF cleaning might have resolved the problem, possibly a leak in the MAP sensor o ring area.
then again there could be an intake manifold leak also, for the P0068 , check the power brake booster vacuum hose.

https://www.obd-codes.com/p0068

skysailor

Yes, open loop was explained to me. And the fact that the problem is happening in that phase has everyone baffled. The sensors can't be blamed. I have not done anything with the O2 sensors and will mention it to my tech. Thanks.

skysailor

Thanks Oldblue but I replaced the throttle body completely with a new one at the start of this debacle when cleaning did not get any good results thinking the attached sensor was faulty, :) MAP sensor with new O-ring also installed way back at the start of things. Tech says he's done a complete vacuum system check and all is OK.

Oldblue

You don’t mention the MAF sensor, is that new also?