So the RPM's bounce around at idle? Always or rarely?

You can test for leaking injector seals by spraying them with something like wd-40, noting any changes in the RPM's.

 

The RPMs bounce around very rarely at idle. It has been months since that last happened. I had thought it was unrelated to the usual stall but who knows.

 

Maybe something important here. While highway driving after 1-2 hours, had a sudden loss of power, then 1 second later, revs came back up. The check engine light came on but had our normal codes 231 and 121. The mass airflow sensor has checked out okay so not sure why that one would come back on.

Also, after highway driving, the idle has been high in park and neutral. Someone said it may be the idle control motor?

 

Well we cleared the codes and just yesterday the CEL came on again. Nothing seemed wrong with the car this time. It was only code 1-2-1 for air mass meter. The air mass meter was checked out fine by a shop the last time but the code keeps coming back. Anyone know what could be wrong here?

 

1-2-1 is suggesting a wiring fault, I would clean up the connector at the LH ECU (behind passenger kick panel).

 

I cleaned up the LH ECU connector yesterday as well as another connector that was right in front of the LH ECU. I believe uplugging one of these cleared the CEL codes?

Then I started up the car to see how it was running, opened the hood, looked and listened. It wasn't too bad, but I decided to disconnect the AMM. When disconnected the idle was MUCH better and smooth. The AMM was checked out okay by a volvo dealership several months ago and it showed signs of being checked out/cleaned with dielectric grease on the pins. Could it be the wiring between AMM and ECU that is causing all my codes, bad idle, and intermittent stalling?

When I cleaned the LH ECU connector I only used a wd-40 type lubricant as I didn't have dielectric grease. Is this a problem or should I do it over with dielectric grease? Cleaning the connectors didn't seem make any difference.

 

Oh, I also wiggled all the wiring between the AMM and ECU that I could find while the car was running. But that didn't result in anything different happening to the idle.

 

Only plug/unplug the AMM with the battery disconnected or you risk causing more damage, plus the ECU memory needs cleared (by removing the battery) each time - codes will be erased and a new map will be created, which is what you want.

wd-40 is bad. Dielectric grease on low voltage circuits only helps to reduce corrosion, long term. You want all your connections to be CLEAN.

The Bosch part number on the AMM should end with -016. It has 5 main wires:
brown/black - ground
green-yellow - ground via ecu
red-white - output voltage
white - burn off wire
orange - supply voltage from fuel/system relay

 

Okay. I just read that wd-40 can leave a residue on electrical contacts. I will clean again with a contact cleaner or isopropyl alcohol.

Should I clean the dielectric grease off the AMM connector or does it not matter?

 

Me personally? I would clean both (everything)

 

The AMM is a Bosch and ends in 016.

And suggestions on the high idle following highway driving? It has never done this before until several weeks ago.

 

Okay, for this I have been told it is a sticky IAC valve by 3 different sources.

 

Its possible to clean them out with non-corrosive cleaner and a q-tip.

 

And one source it is the TPS.

 

How's the connection at your EZK? Is your FPR in good shape? Pull off a vacuum line on your FPR and see if any gas or residue comes out. Check the wiring on your CPS, they tend to go bad randomly. Does the stalling happen when you press the brakes? Clean out your IAC and check all your vacuum hoses that are under the manifold.

 

Ended up bringing it to the shop. They replaced the AMM and a ton of our idle issues were solved. Will just have to wait and see if it stalls or gives anymore codes in the future.

 

From my recollection, you can listen to the in-tank pump at ignition "On," and it will sound like a low, constant hum. You said it sounded strained or something like that? The main fuel pump emits a louder whiney, tinny whir. You cannot start the car with a faulty main fuel pump, but you can start the car with a faulty in-tank pump. A faulty in-tank pump may be your problem, making the main fuel pump work harder, and perhaps causing your stalling issues.

Also, of course, do all the usual tune-up procedures: new spark plugs, new distributor cap and rotor, new spark plug wires.

 

Just an update: about 1/2 year later and no stalling or idle issues. All seem to have been solved by replacing the AMM.