Vacuum Nightmare

[SnakeyesTx]

I've been meaning to post this for weeks but didn't know exactly how to describe it so here goes :

I'm pretty sure this is vacuum issue, but it happens a LOT more often on colder days (like below 65 degrees or so). First start in the day, motors cold, idles HORRIBLE and bucks (you've probably heard me mention this before). Once it warms up it settles down a little bit, but if I sit at a light for a long period of time, the check engine light will come on, and it'll buck pretty violently again, sometimes so bad the engine stalls. The engine code is for the oxygen sensor, go figure (I replaced this already).

When the light is on, the acceleration is poor. I found that if I goose the throttle a few times in neutral up to about 4k rpm and let it rev down (effectively pulling the vacuum away from the extremeties of the engine) the light will go away until the next time I sit at a light for a long time again. Another tipoff to the vacuum idea is because the air conditioner reciruclator flap will thump into place after taking about 8-10 seconds after pushing the button.

On warmer days its not as prominent (The bucking and CEL) but it still happens after sitting at lights.


Weird huh? More sensitive in colder weather, more violent in colder weather, and vacuum issues. I average 16.2 mpg with this new motor where I got well over 19 with the old one. I also have a line missing off the underside of the intake where about a 3/8" vacuum line goes but I can't find any exposed accessory missing a vacuum line anywhere else. Milkboot's M50 has the same missing line but no issues like I do.

So.... wtf?

[BillionPa]

could also be the oxygen sensor heater relay, did you do a starting fluid spray test already?

is that missing line plugged? (could it have gone to the charcoal canister purge valve?)

[SnakeyesTx]

could also be the oxygen sensor heater relay, did you do a starting fluid spray test already?

is that missing line plugged? (could it have gone to the charcoal canister purge valve?)

I did change the o2 sensor relay actually, I did forget to mention that one. I'll try capping the line. If I remember correctly, I saw a picture of JonK's motor with one of those tiny little filters on the end of the nipple I'm referring to.

[Morgenster]

Did you try a reset?
If the problem persists it's vacuum. If it comes back only gradually then it's likely a sensor out of whack. At least, that's what I think about testing for idle problems.
Mine does something similar and I think the TPS is cause nr 1 because it registers 1,8k ohms with throttle closed making the DME think it's open.

[BillionPa]

that would indeed cause rough running due to fuel enrichment, and lower the mileage significantly (complete opposite of vacuum leak, but similar symptoms)

pull the spark plugs and check the condition to see if you can tell whether its running lean or rich, as a CEL that goes away generally wont tell you.

[e34musician]

If all the sudden the car idles really bad (not idle rough all the time) and the car almost stalls or stalls. When the car stalled, did it start right back up?

This could be one of the MAF fail mode that I just had on my car. See my tread here.
http://www.bimmer.info/forum/showthr...t=31926&page=4

If you can read and reset the code fine, you may want to try disconnecting MAF harness to see if your car runs better (in safe mode).

Good luck.

[SnakeyesTx]

The only code I get is O2 sensor which was recently replaced. The O2 sensor heater relay was replaced as well. When the engine stalls, I can restart it easily. I'm really thinking this is a vacuum issue here with the A/C recirculator valve thing.

[Morgenster]

The only code I get is O2 sensor which was recently replaced. The O2 sensor heater relay was replaced as well. When the engine stalls, I can restart it easily. I'm really thinking this is a vacuum issue here with the A/C recirculator valve thing.

Still, did you try the reset?

[SnakeyesTx]

The ECU? Yes, twice.

[e34musician]

Did you try to unplug your MAF sensor? You never know. I spent the whole week resealing the intake and vacuum hose. It turns out it doesn't fix my problem.

MAF could throw off your mixture, hence rough idle, stall ....