Engine Stumbles then Falls on Face

[carguy101]

As the title says, my engine will stumble then almost stall but never quite do it if I press the gas and depress the clutch.  I just replaced the valve cover gasket and lower pan gasket (to check the oil pump bolts thankfully they were all tight thank God!) as well. I dont know it that matters but I also noticed that the breather hose off of the valve cover was not connected at the other end and I re-connected that to the only place I could make sense to where it would go. It will sometimes not have the smoothest idle either. The engine will rev normally sometimes and then other times it sputters then gains power then stumbles then goes again. It usually does this under 2k but sometimes all the way through 3200. It really only does it 3/4 throttle or more or less than 1/4 too. I can drive slowly and only have a couple hiccups here and there and not have the bucking bronco and sometimes under full throttle it will be ok, I have only taken it up to 5k though.I am thinking that it could maybe be the plug wires from moving them around may have broken something, doubt it but I do not know when they were replaced but the previous owner says he did. I dont think it is a vacuum leak but I would not be surprised because the hose that goes to the ICV needs to be replaced but I couldnt image it would be this erratic. I also changed from 15w50 to 20w50, could that possibly do anything like that?

I hope that made sense...
TIA
Jeff

[DesktopDave]

I think you're on the right track.  Vac leak or sticky ICV.  I've heard they can be cleaned with a little TB cleaner.  You can test them with a 9v battery too...it'll snap open if you give it 9v, and hum if it's working right.

I'd also check to see if the throttle butterfly was clean & the accel cable not broken or pinched.  I had a rusty one with a broken collar that would stick then not re-seat on my old 325is.  RTV didn't fix it but there's a little BMW wire clip that does.  It was a recall item in the late 90s, your local dealer might know about it.  Couldn't be more than $1.

If neither of those help, check the AFM door for smooth function or the main air hose for cracking.  They have a little resistor track that wears out too, that'll cause trouble.  You can test that with a multimeter set on ohms.

[charbel]

check your MAF. or like you said. vacum leaks.

[fiftytakedowns]

I tested my Afm recently and the ohm change was smooth but it te numbers changed value along a bell curve  if that makes sense? what numbers should I be looking for? manual was not specific.

[carguy101]

ok the weirdest thing.... it fixed itself and runs just fine. I think there may have been a lil corrosion on the wires when i was cleaning the engine and after i cleaned them just a bit it ran even better... i know wtf but it works just fine now lol