SOLVED - (2004, 4.4i) Idle surges up, drops to almost stall then just stumbles

[Purplefade]

Solution Update - my problem ended up being caused by a faulty oil filler cap that was just loose enough to cause a significant vacuum leak to the point that the car barely ran\idled.


Symptoms:
- Idle surge to 3000 rpm on startup

- Final idle after about 90 seconds was so low and unstable the car barley stayed running
- - Initially I had NO CODES - it was a mystery - -

- Finally after much trial and error I got multiple misfire codes and the car started to run and smell terribly rich - which really pointed at a vacuum leak








Morning Xoutpost - I've got a strange one that I can't seem to track down, it's persistent and doesn't seem to throw codes - which is driving me insane.


Ok, the issue: - On ANY START, not cold, not hot, any start, the car will start fine, immediately "spike" up to 3000 RPM and then drop to just under 1000 RPM over about 3 seconds and then about 90 seconds after that it drops to about 700 RPM. All of this is normal for the car except the jump to 3000 RPM part, it used to just start, grab idle and hang at about 1000 RPM for 90 seconds until it warmed up and dropped to 700.



It's what happens after that, that is the bigger issue. Once low idle sets in the RPM will slowly over about 15 seconds climb to 1000 RPM and then drop to almost stall, level off for maybe 30 seconds (though it's still a bit rough), climb to 2000 RPM and then act like it wants to stall again.


This cycle will repeat itself over and over, the car won't stall but it won't idle either - and if you just put it in gear and drive away - it seems to run fine - not down on power, doesn't lag, doesn't fall on its face, miss or other, seems to run fine -> but won't idle.


So far I have:
- Changed the oil, just for giggles sake
- Pulled and re-seated the vanos solenoids & solenoid plugs

- SUPER cleaned the MAF and Throttle Body (with MAF cleaner specifically)

- And ran a hand along all of my vacuum lines, ports and plugs
- Swapped cam position sensors to try and isolate it to a sensor or bank
- Checked and cleaned the CCVs (lines and diaphragms)



And nothing made even the slightest difference?? At the moment, I'm stumped...



Thoughts?

[andrewwynn]

Can you read realtime values on the throttle body? My bet is on a bad sensor for the throttle body position.

[StephenVA]

If you plug in a code reader that can show real time info you are going to see weird TPS% numbers happening. +1 on the TPS sensor going south.

[andrewwynn]

Think of an old radio volume knob that is staticy. The sensor for tps is the same thing


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[Purplefade]

That makes total sense! Now I'm used to the TPS sensors that bolt to the side of the throttle body vs ones being integrated, but I definitely know what you are talking about.


Is the TPS serviceable in this unit or do I have to replace the entire TB?



I will break out the old Foxwell this evening and see what pops up on that TB real time data.

[andrewwynn]

According to BMW whole assembly but I think you can replace just the sensor

[Purplefade]

I thought it was Clockwork - may be time to try this, if I have to replace the entire TB :-)


https://xoutpost.com/bmw-sav-forums/...3-n62b44a.html


Haven't yet had a chance to get to the garage, still hoping to get out there after dinner... but I think my wife thinks I'm laying flooring... wish me luck (with the flooring)

[EODguy]

Have you run it with the MAF unplugged? Sometimes cleaning doesn't work and I had about the same issues as signal was enough to screw things up but only got codes occasionally...

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[andrewwynn]

+1 on unplug MAF it's a good control


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[Purplefade]

Thanks guys!


Ok, finally... got back in to the garage and managed to get an SES light, but not at all for what I expected.


Codes Pulled:
- Multiple misfires on multiple cylinders
- Misfire on 1, 3, 5, 7, 8, and 2



So, it still won't idle smooth but has stopped fluctuating, it just stays a flat "I really want to stall" now and smells insanely rich. I can "poke" the peddle and get it to jump up in RPMs and if I catch it while it's up I can hold the RPM there but slowly depressing the pedal results in it stumbling and wanting to stall.



- I have pulled the MAF (again) - no difference - I super cleaned the MAF (again) - no difference
- I pulled and cleaned the TB - no difference

- I pulled values on all 4 O2 sensors and they appeared stable and not erratic
-- Pre Cats matched almost perfectly which I initially thought was a bit concerning but then so did the post cats

- I checked the grounds on the VCs just for giggle sake and didn't find anything that concerned me
- Pedal value and MAF went up almost linear in my live data stream
- And both pedal trim-pot values also seemed stable and not erratic


-> All that said, I did find that the hose on the top of the vacuum pump "wiggles" and on closer inspection it appears that the metal top plate of the vacuum pump nipple itself is "cracked" as I can see a small amount of seepage coming from the area that appears cracked.


Could that really cause the issues that I am experiencing or did I just run in to something else I need to fix while I'm in there still searching for the root cause of this issue?