Help! Intermittent no-start, fluctuating idle RPM issue

[dyslexic zombie]

Hi all!

My non-vanos 540i has been running like a champ until recently when I parked it for a minute and it would not start back up. Here's a list of known symptoms and fixes I have tried:


- Car starts up almost normally when its cold, 60F outside temp or less. When the engine is warm or the car sits in the sun, it will crank and crank but will not catch and fire up. Spraying starter fluid in the intake does not help it start up when its warm.

- when it is running, the idle RPMs will randomly fluctuate, jumping up to 1000-2000 for random periods of time before settling back down to a normal range, only to jump back up again. The random jumps continue to occur if the car is driven-- a bit dangerous really.

- there are occasional misfires, and there is a vacuum leak at the throttle body gasket; I have ordered a replacement, but it seems to me this could cause misfires but not the idle problem or the no start problem.

- there is an oil leak around the coils, so I've ordered new valve cover gaskets but not installed yet. I cleaned up all the oil, de-greased the coils and re-installed with new spark plugs, only to find the no-start and idle issues unchanged.

- I replaced the CVV and gasket, no change in symptoms.

- I checked all the related fuses and relays in the trunk and under the hood and swapped them out, no change.

- I replaced the ignition module under the steering wheel, no change.

- I removed the DME, inspected all the pins, took the DME apart and inspected the board to find no evidence of corrosion or water intrusion.

- I thoroughly cleaned out the ICV until it actuated freely and reinstalled, no change.

- the ABS and ASC lights are on. I don't care at all about the ASC, I always turn it off anyways, and I'm not super concerned about the ABS unless it might be causing the no-start or idle issues. Don't see how it could.

- only codes being thrown at the OBDII port are misfires, and a temperature sensor code that went away when I bled and topped off the coolant system

From the research I've done, I'm thinking the crankshaft pos. sensor, or the camshaft pos. sensor. They aren't exactly cheap to replace, so I'm hoping for some more input before I commit. I might think it was a fuel system issue, except it starts up and revs fine when cold. Anyone have any suggestions/advice? Anyone experienced a similar problem?

[blackknight530i]

I just ran into a similar issue on my M5. Turns out the ground wire for the DME that attaches to the strut tower on the passenger side was loose. The nut had backed out maybe 1/4 turn or so and it was causing the car to not start at all. Worth a try and an easy fix. Mine died in the middle of the road and it totally makes sense now as I was just accelerating from a stoplight when it happened.

[dyslexic zombie]

Thanks for the reply

Checked the DME ground wires and the nut was tight, but it looked dirty so I took it off. Sure enough, a bunch of crud had crept under the contacts and corroded them. Cleaned them off and she started right up. Purring as I type, no idle issues so far... That might have done it!

Will try a warm start once it reaches temp.

[blackknight530i]

Thanks for the reply

Checked the DME ground wires and the nut was tight, but it looked dirty so I took it off. Sure enough, a bunch of crud had crept under the contacts and corroded them. Cleaned them off and she started right up. Purring as I type, no idle issues so far... That might have done it!

Will try a warm start once it reaches temp.

Wow, crazy. Hopefully it's as simple as that. I was blown away when I discovered my issue.

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[dyslexic zombie]

Too good to be true

Wont start back up warm. Sputters a bit but wont take. Seems like the random jumping idle problem might be fixed though. It idled normally for 10 minutes

Thanks!

[geargrinder]

Hmmm. Seems like the ground wire fixed your idle... you might try clearing adaptations. Sometimes adaptations can get "off the map" and cause weird stuff like that, and I can imagine a theory where a bad ground caused erroneous sensor errors to set adaptations off the map... Basically I'd clear codes AND adaptations then see what re-appears since the ground-fix...

[edjack]

Measure the fuel pressure when it won't start.

[blackknight530i]

I would agree with both above suggestions. GG's recommendation is pretty simple if you have INPA and seems like it would apply.

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[dyslexic zombie]

Well the idle problem came back with a vengeance. Got INPA working today and tried clearing the codes and adaptations. It seemed to work for a minute, idle dropped and sounded better, but the idle problem quickly returned, jumping all over. I don't have a fuel pressure gauge, but will ask around tomorrow and see if anyone I know has one.

Code 123 coolant temperature error code is back, this time with a 139 output thermostat code as well. Will do some diagnostics on the 2 coolant thermostats tomorrow; maybe one is going bad.

Also noticed that total air consumption HLM (30) and needed air is controller (25) are out of range. Smoothness value is really high on cylinder 6, went above 1000 at one point; swapping coils did nothing.

MAF sensor is bosch, looks clean and fairly new, voltage in in range. Thought the vacuum leak was just a small one at the throttle body, but maybe it's worse than I thought. Valve cover gaskets and valley pan kits arrived, so if the thermostats seem ok tomorrow, I may just get started on the valve cover and valley pan job, replace all the gaskets and any old hoses I find along the way, see what it do after that.

Thanks all for the suggestions

[geargrinder]

There’s only one thermostat. There are 2 temp sensors in the dual-sensor dingus. The output error is about the actual thermostat, but may actually relate to the temp sensor indirectly. Aka the DME is getting a wrong temp, tries to change the temp via activating the stat, sees it doesn’t work, and thinks the stat is defective.

If the DME has an erroneous engine / coolant temp for sure it will cause weird poor running. Sometimes the dual sensor can have one side drift / degrade while the other is still good, which has been reported to cause poor running issues. For sure swapping a new temp sensor in is cheapish and easy thing to try....

HowEver, the wide range of sensor errors you are seeing really makes me think there’s some fundamental underlying problem. Like another ground problem. Coolant contamination of the harness and DME pins would be high on my list but you checked that already...

[dyslexic zombie]

My bad, geargrinder, I was talking about the temp sensors. You're right, and it occurs to me now that I'm thinking thermostat, I had my water pump replaced about 2 years ago with a non-BMW brand. Was german-made but I can remember the brand and can't find the receipt. The thermostat is in the water pump housing right? Vaguely remember it getting replaced too. Might be either the old one is going bad or the new non-oem one is going already.

This is getting stranger now. ugh.

Replaced the radiator temp sensor today with a known working one. Still getting 123 and 139 codes, but haven't fully bled the system after the swap yet. Weirdly, the car will start with a hot engine now. Started it 6 times in a row while hot. Wasn't doing that before I swapped the sensor, but given the strangeness of everything else I'm not assuming causality. Ordered a new water pump temp sensor as well, since its inexpensive.

Clearing codes and adaptations seems to have no effect on whether or not the car will start back up, but does cause the idle rpm to change, although the codes immediately are thrown again, and the rpm changes back to what it was before. The random rpm jumps go away for a while sometimes, then unpredictably pop back up again.

I re-checked the DME and all wires and grounds I could find. DME pins are spotless, no sign of fluid creeping up anywhere near the DME, grounds all have good contact.

One cylinder is still getting high smoothness values seemingly at random, sometimes its cylinder 6, sometimes 8, one time 3. I have had it sit and idle one time for 10 minutes without any smoothness readings getting above 400, though usually one cylinder will creep up over 1000 after a few minutes.

Still getting out of range readings for total air consumption and needed air is controller. needed air is pegged at 14-15, total air sometimes drops below the max of 20, but still seems way high for idle, and goes up to 30-35 seemingly at random. Anyone know what could cause these 2 readings in particular? Any sensors contribute to those 2 readings other than the MAF?

Also, I rubbed some RTV on the side of the throttle body where the leak is last night as a temporary fix. Seems to have plugged it, no rpm change when I spray starter fluid on it now. Still hearing an awful lot of hissing around the intake somewhere, though I haven't been able to locate any more leaks with the starter fluid method.

No luck chasing down a fuel pressure gauge yet. May just buy one soon, be good to have one.

[geargrinder]

Yah as menched that rad temp sensor is not the one generating the codes. Swap the other one and see what you get. One side of the dual temp is used for the cluster, the other for engine operation... I guess there’s 2 just for purposes of detecting errors...

You may have a big air leak. But that results in too LOW MAF readings not high. So something is maybe still electrically borked. Either MAF itself or grounds or something.

[dyslexic zombie]

New sensor should get here tomorrow. Planning to at least start valley pan and valve cover jobs this weekend, hopefully will be able to identify the air leaks.

About the MAF readings, I found a thread where someone was having the same readings on their 540i, and ended up learning that the reading were not out of range, rather INPA had incorrect parameters for those sensors, resulting in ! next to the values. Normal for idle apparently is 29, and WOT is 99, meaning that when the air consumption was showing 20-30 as the idle rpm wandered from about 600-1500, it likely could have been giving low MAF readings. Will focus on fixing the vacuum leak for now, once I can confirm with pressure test that all leaks are gone, will worry about electrical gremlins.

Speaking of which, I noticed on realoem.com that the ASC/ABS basic control unit is listed on the MAF page, which is in the fuel injection system section. This has me sweating a bit, as my ABS+ASC lights are on and I don't really understand the relationship btw the unit and the fuel system. Is it possible for a bad ASC/ABS unit to mess with idle rpm? Or fuel delivery in any way while the car is parked? Perhaps I should try unplugging the damn thing...

[geargrinder]

Good research on the MAF readings, and I'd not come across that bit about INPA having some erroneous 'range' errors. Mine always appear to be off-kilter due to my blower/MAF setup so I'm used to an hot-idle number thats more in the mid-teens, which should NOT be what you are seeing.

With the ASC system yes the ASC has an 'extra throttle' on the intake. There's lots of threads on 'ASC delete'... you can just remove the throttle plate, which is easiest, but if you unplug the unit then you need to fake the ABS/ASC into thinking somethign is still there... So... if you remove the whole ASC-throttle assembly, the options are either leave part or all of the module ziptied up in the engine bay (yuck) , or, use a resistor.

I'm not an ASC+non-VANOS expert, but, I've not heard of a bad ASC intervening in idle, seems unlikely since the first thing that tends to happen if the module is throwing lights is that it disables all functions - aka the opposite of intervening... Unless there's some real crazy wiring/malfunction going on surrounding the ASC throttle.

You really want to at least read the ABS codes with a proper BMW-reader device or software and see whats there. With luck its just a bad wheel speed sensor. Its really better to have the system working (even if you want to permanently disable ASC throttle intervention by removing the plate...) and the car is a better driving/safer vehicle with ABS working. Not to mention ABS faults are an inspection fail around here - I'd think in Kalifornia too but maybe not..

[dyslexic zombie]

Yeah all credit to gmak2012 over at bimmerfest for the MAF stuff.

Based on what you said I agree the ASC is not involved since I did confirm that no throttle cables move as the idle wanders.

I do want the ABS working eventually, but right now I'm just trying to get my vehicle running so I can get to work and back. Have a moto i use when weather is good, but six in the rain. Lucky for me I live in unincorporated sonoma county where we dont have to smog cars �� also work is only 2 miles away and all 25mph roads. Not far enough I need ABS, but far enough that riding/walking is irritating in foul weather. Def will check the codes soon tho.

Ongoing support is much appreciated dude!

[dyslexic zombie]

Both idle and no start problems are now fixed. It seems the no start problem was caused by the radiator temp sensor and the wandering idle was the water pump temp sensor. Both bad sensors were bmw originals, new ones are aftermarket from ecstuning.

The 123 code hasn't come back, but I'm still getting the 139 thermostat code. Seems like I will probably have to replace it. INPA readings are about 20% higher than the infrared reading taken at the post-pump coolant hose, not sure if that's normal or not.

Got my hands on a vacuum gauge, car read 16 after cold start at the nipple right next to the water pump, when hot it was literally bouncing between 18 and 20. Still trying to find what the nominal readings should be somewhere online.

Weirdly, my tach is now way off. Shows 1500 when idling at around 700, maxes out when engine is revved past 2500...

Checked ABS and am getting a front wheel speed sensor code and also a can signal error code- hoping they are both caused by the one bad sensor.

[geargrinder]

Huh. Cool. Progress at least.

But I dunno man, I'm still not ruling out some voltage/ground problem thats messing with multiple things?

Yes the 139 is prob just 'face value'... aka a bad stupid MAP thermostat element... They go bad with age, thats totally normal. Keep in mind you can replace the t-stat w/ a non-MAP style, then put a power resistor on the end of the plug to fake the DME into thinking its still there. Then you have a conventional fixed-temp thermostat and overall lower op temps. I can't remember what the part is for a non-TU conversion, something like maybe the M60 thermostat? One of the smarter-than-me guys will ring in and say I bet... or find somebody like Philly's write up of it from years ago...

CAN comms is a fairly isolated twisted pair of wires between a limited number of modules - DME, transmission computer (for slushies), and ABS... its not that commonly disturbed unless the DME connector gets borked. But if theres bad voltage going on someplace, making modules hiccup, that could do it... I assume you cleared the code, will be interesting to see if it comes back. The wheel speed sensor is maybe reason to be optimistic, with luck that'll sort your trifecta problem.

RPM sounds doubled. Can't at all explain how that would relate to any of the sensors changed or mentioned yet though... Unless its related to the CAN errors. You didn't re-code the cluster at all or anything? Weird.

[dyslexic zombie]

Well, I finally had time to work on the car again this weekend. Meant to do it last weekend, but went to a seminar with Dr. Greer last weekend and suffice it to say shit got way too real.

Anyways, no start and idle issues continue to be resolved. The wheel speed sensor did come back, along with a 67 electromagnetic field susceptibility code, though the CAN error hasn't reappeared. Fixing the ABS will be the next project, along with replacing oxygen sensors. (still getting substantial unburnt fuel smell in exhaust) Electrical gremlins continue their mischief. Unplugging the battery seems to have fixed the tach, but now am getting intermittent sound loss from driver side speakers and occasional non-functioning of sunroof switch. Sigh.

Replaced the intake gaskets and valve cover gaskets. Yall would not believe the crap that was caked around the intakes -_-

Rodents had been living on top of the engine, apparently. They chewed up part of my hood liner, packed the insulation into the crevice between the intake and head, nice and warm all night in winter, I'm sure. Naturally, I had to remove 100% of the mashed-in and baked-on insulation, seed hulls, feces, oil, urine and god knows what else before removing the intake, so as not to let crap fall into the cylinders. Prob took 3 hours, many repetitions of spraying degreaser, scraping, vacuuming, blowing, ect. Even had to crush a few small rocks with xl needlenoses that had gotten wedged in somehow.

Got the intake off to discover that all that oil and rodent crap had been getting sucked into the ports through the failing gaskets. Fortunately the 1/8" of sticky black sludge wiped right off with no trouble. Valves themselves look really clean.



Saw that the valley pan was not leaking, so decided to leave it be for now. Will do it when I replace the thermostat.

If I ever meet the person responsible for the choice of finish on those valve covers, I will likely end up in prison. Good lord. 4 hours of very careful, low-rpm wire-wheel, degreaser and sandpaper got the flush surfaces into reasonable shape; the groove is hopelessly pitted. Would have liked to have them refinished, but am pressed for time right now, and need the car running. Is holding oil so far. Cams and timing chains looked really clean, but the underside of the valve covers were caked with black and brown crap. Looks to me like the previous owner was running conventional oil for a while :[ Cleaned it all off before reinstall, but might run some seafoam through it some point to get whatever's left.

She runs waaay better now. Idle is much, much smoother and quite a bit of power has been regained. Think I'm still hearing a tiny bit of vacuum hiss from somewhere, but it's much less. Either fuel injector orings or one of the older hoses I haven't gotten around to replacing yet, I'm thinking.

Many thanks to everyone who has posted e39 info and guides over the years. Was able to fit all the gaskets correctly on the first try and start the car back up with the first crank thanks to the wealth of information yall made available!

[dyslexic zombie]

Been a minute; my bad for not updating this sooner. All problems solved, she is running great now, except for clicking from the driveshaft. Have a rebuilt shaft and tranny mounts on order; suspect it's the center support bearing that's gone bad but just replacing the whole thing.

So the ABS / ASC not working, and the cruise control and the speedometer malfunctions were all caused by the front left wheel speed sensor. Had the sensors replaced along with the tires, and the mechanic had filled my sensor plugs with dielectric grease.
The grease was too much for the sensors and was throwing off the voltage. Cleaned it out with rubbing alchohol and now everything is working fine again.
Never underestimate the simple power of clean electrical connections...