I see this all the time and not just the GM stuff.travis wrote: ↑Tue Apr 27, 2021 5:15 pm The MAF reads .70-.71 lb/m with random spikes up to .75-.80 at warm idle. At a steady no load 1500 rpms it reads a steady 2.39 lb/m +/- .02.
MAP reads a steady 9.7” HG at idle, no spikes at all. About 8.9” at a steady no load 1500 rpms, again no spikes.
Ignition timing at idle jumps all over the place between 20* and 24.5*. It’s a rock solid 28* at steady no load 1500 rpms.
With a computer controlled engine the timing will jump around a lot based on environmental and mechanical conditions that happen so fast and so many times a second to give the very most optimum running conditions. And you see this more on a scanner with no load among other things.
It will seem that vacuum signal controls everything and when it gets out of whats called normal operating parameters which is a very wide margin when it comes down to it to allow the engine to run as designed..........smoothly.
That said water temp exhaust temp ambient air temp mass air flowing into the engine all play a part in the constant adjusts made by the ECM to control the engines idle or power under load from 1st start up through warm up till at operating temperature and so on.
The hard codes trigger the light to stay on soft codes the ECM can work around are the issues that are hard to nail down but good old fashioned diagnostic methods allow us to go through each part of the system but some times ya got to think out side that box back to the days before ECM control.
EG
A rough running idle condition may not trip a code to tell you its the MAP or MAF sensor causing the rich idle condition but an O2 sensor could do it if it does not go through open and closed loop fast enough or slow enough if it is a heated type of sensor. The older TBI engines in GM trucks used a single O2 sensor as well as 2 different temp sensors for the block water temp and the other to operate the dash gauge and while they are not directly linked together they will set a code if unplugged 1 soft and 1 hard code.
While resetting just required the engine off for 30 seconds then the soft code would be gone but the hard code for the water temp disconnection will need a scanner reset to clear and turn of the light.
It could be a dripping injector not enough fuel to trip a code but just enough to create a correcting of the AIM to raise the idle a bit.
Go back to basic's and think about a carbed engine and figure it out 1 step at a time how to fix it.
Then looking at your present engine's issue and figure out what you missed.
But the most over looked area's to check are the ground wires.
They get dirty over time and the system voltage signals are much lower compared to older engines and dirty grounds account for a very high percentage of mis-diagnosed running conditions on today's engines.
Kind of like with a carb the 1st item to check is the fuel filter with an ECM controlled engines be sure all the grounds are intact and clean.
