My car has been garaged kept without driving for about a year after it developed a start-stall issue.

Specifically, it would start when cold, idle for a few minutes and then sputter and die. Some dry black soot also could be seen on the garage floor below the tail pipe (nothing heavy). At that point it would restart only after waiting 15-30 minutes. And then the cycle would repeat.

Fuel pressure is 41 psi with key on engine off and 34-36 psi with engine idling including when it sputters and dies at which time the pressure returns to 41 psi.

I replaced all 6 fuel injectors after a couple measured low resistance (5 ohms instead of 12 ohms). I also swapped out the ignition control module and the coil packs with known good ones and replaced the O2 sensor and spark plugs. No change in behavior. A back flow pressure test didn’t indicate a restricted exhaust.

Yesterday, I unplugged the MAF sensor and started the car. At that point, the engine continued to idle smoothly for about 30 minutes, reaching normal operating temperature with the cooling fan cycling on and off several times. It hadn’t done that in a year. When I plugged the MAF sensor back in with the engine still idling, the engine stalled and would not restart.

After that (I didn’t wait for a cool down to try to restart), I removed the MAF sensor and the housing and there was dry black soot in the MAF housing interior and in the throttle body. Maybe because of so much idling? I plan on cleaning those components together with the idle air control valve which I have not yet removed.

For the past year, the ODB1 codes have been 26 and 27 ( quad driver circuits). And of course 34 after disconnecting the MAF sensor.

I’m somewhat encouraged by the way the engine was running with the MAF sensor unplugged. If cleaning the air intake components doesn’t resolve the start stall issue with the MAF sensor plugged in, do you think the MAF sensor needs replacing? Any other thoughts? Thanks for your help.

I'm thinking with all that black soot, it is running rich. When it gets to operating temperature and transitions from open loop to closed loop, it reacts poorly to this symptom.

With the MAF disconnected, it will never go closed loop, and instead runs off of an assumed map.

I suggest you try running it with one fuel injector at a time unplugged, and see if any one being unplugged makes the issue go away. This is at idle, not driving.

1. Disconnect electrical connector on the fuel injector for cylinder 1.
2. Start and let it run until it would normally die plus a couple of minutes.
3. Did it die?
4. Reconnect electrical connector on the fuel injector for cylinder 1.
5. Repeat steps 1 through 4 for cylinders 2, 3, 4, 5, 6, one at a time.
6. Record the results and report back.

Thanks. I’ll try what you’ve suggested when I get a chance this weekend.

However, I wonder how it can be the injectors that are causing the start-stall after a few minutes w/o restarting until waiting 15-30 minutes issue. I recently replaced all 6 injectors with AC Delco’* and all seem to be working. Nevertheless, the engine has the same issue operating the same as it did with the old injectors, a couple of which had low out-of-spec resistance.

The engine idles smoothly cycling through fan cooling on/off cycles seemingly forever only with the MAF sensor disconnected. So disconnecting the MAF sensor resolves the issue.

Oh yeah, I missed that part in your original description.

I'd still do the test.

The issue seems to me to be possibly related to whether the engine running open loop or closed loop.

Thanks for confirming.

I just want to be clear, however, that with the MAF sensor connected, the engine will start and idle but will not reach operating temperature before stalling. I’m not exactly sure how to define “operating temperature”, but the radiator hoses are relatively cool to the touch when the engine stalls.

in contrast, with the MAF sensor plugged in, the engine presumably reaches operating temperature because the cooling fan will cycle on and off while the engine idles indefinitely (i.e, no stalling).

Apologies. The last paragraph in my last post should read “with the MAF sensor UNPLUGGED the engine presumably reaches operating temperature ….”.

The point I was trying to make in my last post is that with the MAF sensor connected, the engine doesn’t seem to reach operating temperature when the engine stalls and won’t restart for a while, and thus, doesn’t reach closed loop operation. So it doesn’t seem to be an issue of the engine getting to operating temp and transitioning from open loop to closed loop that is causing the engine to react poorly to the back soot/ running rich symptom to which you refer.

The engine can't transition from open loop to closed loop while the MAF is disconnected.

It could be that the MAF itself is bad.

I'd check the injectors first since it'* cheap and easy.

1990 Buick Skylark with a 3.3l ?

also, if you have the MAF attached and you jump a and B of the ALDL (like youre going to flash codes) AFTER the engine is running, the MIL will flash at a variable rate, a video of that when up to operating temp, starting in park then a small tid bit at steady cruise where you can safely grab a small clip. Post those videos to here if you can or youtube and link, or imgur if you dont have a YT acct

Yes, 1990 Skylark 3.3l engine. Thanks, but I won’t be able to capture such a video because, with the MAF sensor plugged in, the engine will stall before reaching operating temp. If it doesn’t stall before then it will mean that my having cleaned the sensor and other components/sensors at the air intake (which I plan on doing this weekend) solved the stalling issue.

so you need to either fix the wiring to the maf sensor or your MAF Is bad

Unless your MAF Is fine but you have a profound amount of unmetered air such as an intake gasket or a throttle body gasket

Unlit propane torch around the idling motor around the tb, intake can clue you in to this. But only do this with the air duct all on , becuase you wouldnt want to wave it in front of the TB and think you found a leak but it was just being sucked into the TB

The duct and filter being attached allows you to wave it near that area