Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Hi there, I am Cam. Sorry to hear about this issue. When you replaced the intake, did you also have a new throttle body with it?
Was there carbon or debris plugging up the ports on the throttle body?
Is there a check engine light set when its idling like this?
OK, so code P0442 or P0455, did you check the codes after this issue started happening?My thought process is that there is a fault with the wiring or connections for the idle air motor and that its not opening or operating. If this is the case, this would be your issue. That motor's job is to let air past the throttle plates to control the idle. We need to verify that wiring and verify operation of the idle air bypass.
It's all based on idle though. The fact it changes with being parked different ways makes me wonder about loose wiring or connections.
It may also be a bad oil pump or pick up. Have you verified oil pressure with a manual gauge? If not can you please do that and get exact numbers.
I agree with that then. So let's focus on the idle. Check out the operation of the idle air motor next.
Do you happen to have a scanner that can view data then?
You would be looking for the desired and actual idle speeds. I do need to know which throttle system to you have, is it the cable or only the electronic throttle? That could change what I suggest and that around the year things changed over.
Also can you see what the map sensor reading is at idle.
Ok, what is the map reading at idle?
What happens to the idle if you unplug that map sensor?
Did the idle settle to normal then?Also if you unplug the Mass Air Flow sensor (MAF) sensor, what happens?
And that MAP reading, what units?
What is the g/s on the maF when running?
That fits the idle speed.. Is there any chip or aftermarket devices installed?Whats your fuel pressure?
No scanner can read fuel pressure. you need to plug in a pressure gauge at the test port on the passengers side of the fuel rail. Another thing you can also check is the vacuum line on the fuel pressure regulator on the drivers side of the fuel rail on the intake. Is there fuel present in that line?
whoa, that’s a little low. Spec is 55-62 psi. If you restrict the return line, does it go back up?If you unplug that vacuum line from the regulator, what does it go up to?
What is the 8th digit of your VIN?
So flex fuel, still that pressure is a bit low. IF you unplug the vacuum line at idle, does the idle return to normal?
OK, spec for flex fuel is 48-54 psi with the engine off, pump running. SO we may be in spec.So that system is good then at this moment.So we need to look through this next document.
as long as it remains in that range its good. When running it will drop normally by 3-8 psi. So running if the pressure never goes below 40 then its good.I would take a moment and check ground wires on the back of the engine block and on the frame under the drivers door.
That’s why I am thinking it’s an issue with wiring that moves with the gravity or movement of the truck or possible vacuum lines and such.
With it running, does wiggling the wiring all around the engine change how it runs?Have you tried a reset after all this?Take the battery cables off the battery, hold the ends together for 10 seconds then attach them to the battery and see what happens. This will reset the whole vehicle.If you have 2 batteries, then remove both and touch only one set. This reset is more about touching the cables together when off the battery than taking them off. The act of touching them drains the capacitors and forces it to reset.
OK did you go through the diagnosis I posted in the last document a couple replies ago?
Was the throttle body AC Delco or aftermarket?
Clean the throttle body out then. Use a rag and cleaner to make sure the bore and plates are clean then reset the computer again. I thought the throttle body was new.
With the throttle not changing it at all, I am left with 2 possible causes. First the MAP sensor on the intake manifold may be failing to read accurately. They are not that expensive, I would change that. IF it does not correct it then we may be looking at a bad Powertrain Control Module (PCM). Why the truck being nose down vs nose up makes a difference is strange. I would have thought a loose wire connection, corrosion in connectors or something like that would have been the cause. Its possible there is an issue inside the computer then. A tap test may reveal it. Tapping on the housing of the PCM may cause it to stumble. IF it causes it to change, that’s a sign for sure its bad. IF there is no reaction, that still dow not rule out the PCM.