328i, Low idle for couple of seconds when revs drop after declutching

[keykey]

Hi, i just registered and I'm new to these forums!

I have a very specific problem with my -95 328i Coupé (M52B28 engine, manual trans). When i'm slowing down for a stop, for example approaching a red light, and declutch (/push the clutch pedal to the floor), the rpm's drop lower than they're supposed to, sometimes so low it almost stalls (If i declutch to shift down during a turn, sometimes the power steering strain on the engine makes it die during this drop).
Most of the time though, it "catches back up" and stabilizes, and after that the idle is perfect. (Right rpm, no jumping)

No starting problems, no hesitations otherwise, problem happens only when at operating temp (exactly in the middle of the temp gauge, before that, no problems), no power loss, no misfires, no CEL/DTC's.

What i've done so far that i can remember:
*Replaced spark plugs
*Replaced Crankshaft position sensor (half a year ago because of DTC/another problem which disappeared after replacement)
*Removed and cleaned out IAC Valve + tested (with Bosch KTS670 actuation test, works fine)
*Cleaned the throttle plate with brake cleaner
*Removed PCV Valve/oil separator, disassembled, cleaned, checked for leakage, checked function)
*Removed MAF and visually checked the hotwire for contaminations, looks clean/like new (Air filter is original, NOT cai or KN)
*Removed battery cables (to make sure no adaptive values are left from the bad CPS)
*Replaced rubber intake hose between MAF and Throttle body (dry cracks)
*Just passed emissions/inspection


Possible causes/tips i've read about on forums:
*Speed sensor in diff case (Interesting tip, any more info on this?)
*O2 sensors (don't think so, passed emissions fine, no power loss or excessive fuel consumption)
*Camshaft position sensor (Not sure about this? But no DTC's and no other running problems whatsoever)
*PCV Valve (Cleaned it out yesterday, checked function, no leaks/cracks in the membrane, seals fine if you suck on the intake end and block the other two)
*MAF sensor (visually checked out and no running problems otherwise, but of course that's no guarantee it's not this)
*Clutch dragging (Not this, happens even if you put the shiftlever in neutral after disengaging clutch)


I work as a Mechanic/Car Electronics Technician. I diagnose/fix problems like this everyday at work, but i still can't figure out this damn problem with my own car!

The problem with diagnose is that it's very intermittent. It only happens when declutching and letting the engine rpm's drop, mostly seems to happen coming to a stop, if i do it while rolling with a bit of speed it seems less likely to happen if at all, that's why i'd like more info on the "vehicle speed sensor" theory. I've owned the car for half a year, and ONCE in this time, last week it stalled while parked, had been idling for ~3 minutes (just like it did when the CPS was broken), that gets me confused about the VSS thing though.

I hope there are some experienced BMW guys here who can shed light on this extremely small but very annoying problem!

[bimmerrder]

AH HA! i think you have the exact problem im having! when im slwoing after i delcutch the rpms drop down really low for a seconds then bouce back and this repaets a few times the needle bounces up at down between normal idle and around 200 rpm....ive noticed it happens mainly when i touch the brakes so i think it may be a small vacuum leak in the brake system?

hope someone helps us get this solved! yours sounds worse than mine howeverive never had mine even come close to stalling....that must be really really annoying....

[jmo69]

I won't be any help either, my rpms hang for a split second after lifting my foot off the gas before dropping making it hard to shift.

[JPJ]

You have a lot of people reading this thread because they have the same type of issue....including me on my 95 M3.

I saw another thread (that didn't end with an answer) but suggested all the same things you have tried. I suspect my O2 sensor is pretty old, so I will try replacing it plus a new fuel filter since I don't know when it was replaced either.

[keykey]

I won't be any help either, my rpms hang for a split second after lifting my foot off the gas before dropping making it hard to shift.

That sounds like a vacuum leak, have you tried spraying the intake area with start gas (for example CRC Motor Starter)? If the engine speed increases you have a vacuum leak. Check PCV hoses and vacuum hoses.

Also be sure to inspect the rubber "air duct"/intake hose that goes between the MAF and throttle body closely, remove it completely and stretch it, feel with your fingers inside the hose and visually inspectit for cracks. Very common on M52 engines.

[GHit]

I have the exact same problem. I just replaced all of my o2 sensors, fuel filter, and new crankshaft sensor as of 6 months ago or less. I think it may have something to do with the camshaft sensor or MAF. As with your problem, mine is intermittent as well. Im going to order the camshaft sensor, and clean my MAF, i'll let you know how it goes.

[keykey]

I have the exact same problem. I just replaced all of my o2 sensors, fuel filter, and new crankshaft sensor as of 6 months ago or less. I think it may have something to do with the camshaft sensor or MAF. As with your problem, mine is intermittent as well. Im going to order the camshaft sensor, and clean my MAF, i'll let you know how it goes.

I'd really appreciate that!
I can't afford any "buy n' try"-repairs now.. I bought the car back in september and i've done all the necessary preventative maintenance since imo the car was a bit neglected by the previous owner. He had been driving it for 3 years with the broken CPS, (engine stalling and jerky behaviour) without even reading DTC's once. It would have been so easily fixed, but i guess he couldn't afford leaving it to a shop. He told me that all he had ever done during his ownership was changing the oil/filter once a year, and replaced an ABS-sensor once.

What i've done to it since i bought it (minus the things in the first post):
*Replaced all tires (it was lowered without doing an alignment)
*Put on an FK Automotive High-tec sport suspension kit (right side dampers were completely dead, rear started leaking a lot first time i put it up on a lift @ work, i guess it's not been raised up a lot during his ownership...)
*Replaced rear shock mounts with reinforced ones
*Replaced rear trailing arm bushings
*Replaced right front control arm rear bushing (will replace the left one too)
*Replaced eccentric camber adjustment bolts (broke off when i tried to loosen them..)
*Four-wheel alignment
*Replaced water pump (with metal impeller, the old one was orange plastic), thermostat, thermostat housing, coolant.
*Oil/filter
*Diff fluid & crush washers on plugs
*Replaced microfilter (probably never done since the car was new..)
*Rear brake rotors, pads, handbrake shoes+mounting kit
*Took apart front brakes and cleaned calipers, lubed float pins
*Replaced long hoot latch wire from inside car out to the latches (PAAAIN in the ass job! But well worth the effort if it risks breaking off...)
*Replaced light bulbs in light switch + OBC (also tried to do the OBC pixel repair with 3M tape, it didn't get any better, i think i used too thick tape strips)
*"Fun"/unneccesary stuff: Debaffle/desnorkel, "golf tee mod", FK crystal white/red rear lamps with philips silver vision indicator bulbs, Osram Diadem indicator bulbs in front, Repaired cracked fog light.

What i want to/plan on doing when i can afford it:
*Fix the rust in the wheel wells (i live in sweden.. salted roads!)
*Replace radiator (never replaced, still has a sticker with "95" on the side!)
*Replace valve cover gasket
*Replace PCV valve/oil separator & hoses with new parts
*Replace silentblocks
*Replace shifter linkage bushings
*Replace tranny fluid with Redline D4 ATF (heard it's good, has anyone tried it?)

Some pics of the car and working on it:



Getting some new legs



Old & new legs




Replacing hood latch wire



FK Crystal clear rear lamps




Comparing old lamps with new lamps



Using Bosch KTS670 for some diagnosis



Sun alignment, screen currently showing caster camber and toe angles in the rear suspension



Our sensors almost didn't fit because of the lowering suspension, it almost touches the wheel well!

[randomy]

any updates?

[RadarLow]

that alignment sensor problem is funny, mine was the same but goodyear straps the gizmo onto the rim with a rubber pad, then does the work, lifetime alignment for 125 was the greatest thing ever for me, strut replacement, bushings, etc. i get a new alignment every time

[keykey]

I have the exact same problem. I just replaced all of my o2 sensors, fuel filter, and new crankshaft sensor as of 6 months ago or less. I think it may have something to do with the camshaft sensor or MAF. As with your problem, mine is intermittent as well. Im going to order the camshaft sensor, and clean my MAF, i'll let you know how it goes.

Hey GHit, did you replace the cam position sensor on your car? Did it help? I still have this problem... and I'd reeeally like to solve it! I tried cleaning my MAF with MAF cleaning spray but it already looked very clean, it made no difference. =(

[Pierre3400]

I have this same problem, and its starting to piss me off!

I replaced the o2 sensor also, but was told to clean the idle regulator and see if it helps, but its placed so bad i just havent had time to take it apart.

Air leak seems possible but i cant seem to find any leaks on my enigen!

[keykey]

I have this same problem, and its starting to piss me off!

I replaced the o2 sensor also, but was told to clean the idle regulator and see if it helps, but its placed so bad i just havent had time to take it apart.

Air leak seems possible but i cant seem to find any leaks on my enigen!

I've removed and cleaned my ICV, connected a Bosch KTS670 diagnosis computer, done a actuator test on the ICV, it works fine but it didn't help the problem. Also removed the Cyclone valve/oil separator, took apart and cleaned. Didn't help (the oil trap cleanup helped get my oil consumption down though).

I'm thinking about asking my boss if i can borrow the MAF-sensor out of the next 6-cyl E36 that comes in at work and go for a test drive with another MAF. The only thing i think is weird if it's the MAF is that the car runs great otherwise.

[keykey]

Bump/Update 2013-03-11 (4 years later):

I Still have the car, still have the problem. Things done since last post 2009-05-19 and lots of fun driving in between + one collision and repair later:

CPS replaced again (the new one broke, same code no problems since)
Fuel pump replaced (VDO/OEM complete sender unit)
Fuel filter replaced
VANOS overhauled with Beisan Systems seals + valve cover gasket
4 emissions inspection passed since (though i tricked the emissions inspector to measure in the right pipe by putting steel net around the left tailpipe)

note: i have a "true" dual system = 3 cylinders to left pipe, 3 to right. A/F ratio points toward lean in the left tailpipe (~1.04 @ 2500rpm, ~1.06 @ idle), but 1.000 (14,7:1) in the right pipe, but i still can't find any intake leaks whatsoever!

Does anyone have anything new to add to this? I feel like I'm gonna own this car forever, I'm too curious about this issue :P

[NikZ3]

If you have checked all the sensors like CPS, ICV, CCV, MAF sensor, oxygen sensors, TPS and you are totally sure that all of them are in good working order and you are sure there is absolutely no vacuum leak in your engine hood and you're still having idle issues then you could check the external crank pulley vibe damper too (P/N : 11231738620).
If it is failed there are bad idle symptoms.
But it's not cheap so you better find a used good one first and then replace it. If the idle issues stops then you know what you have to do.

[janar08]

Any updates?
I'm having the same issue and it scares me to know that you haven't been able to fix the problem in 4 years.

[keykey]

Any updates?
I'm having the same issue and it scares me to know that you haven't been able to fix the problem in 4 years.

2013-08-30
Latest Update:

Still have the car (tried to sell it, but didn't get what i wanted so kept it)

Done lately:
Swapped MAF-sensor with a known-good genuine BMW part from a car that drove good and didn't have this issue, no change so definitely NOT the MAF's fault.
Replaced both O2-sensors with two brand new Hella Units, problem still persists so not the O2-sensors fault.

Plugged the vacuum line going to the vacuum-canister for the exhaust flap directly under the intake (because some people claim this fixed other issues), and actually i think it got slightly better, during the test drive after doing this i really provoked the car so the rev drops would occur, it still dipped but it only dipped below the 500rpm-line once and didn't stall once. I think i have to drive more to know if it's placebo or not but it felt better.

[JPJ]

I was subscribed from posting on this thread from 4 years ago and saying I had a similar issue. I don't any more, but can't say what made the difference and have made a lot of changes (it's a dedicated track car now).

Have you looked at swapping the chip? Is it the original one in the car? Maybe try something aftermarket - you can pick them up cheap used.

[keykey]

Have you looked at swapping the chip? Is it the original one in the car? Maybe try something aftermarket - you can pick them up cheap used.

Yeah, I've considered it. I've even emailed a dealership getting an estimate on a DME Update, because I don't think my DME has ever been updated but i would really like to know what's changed in between updates and which updates are available for the M52 but it seems impossible to get any info at all on DME updates..

I've considered aftermarket chip's too but the market is not that big on them here in Sweden.. I'm also unsure if I have a loose replaceable chip or a soldered, but from what I've read, it's soldered.

[illbeedat]

2013-08-30
Latest Update:

Still have the car (tried to sell it, but didn't get what i wanted so kept it)

Done lately:
Swapped MAF-sensor with a known-good genuine BMW part from a car that drove good and didn't have this issue, no change so definitely NOT the MAF's fault.
Replaced both O2-sensors with two brand new Hella Units, problem still persists so not the O2-sensors fault.

Plugged the vacuum line going to the vacuum-canister for the exhaust flap directly under the intake (because some people claim this fixed other issues), and actually i think it got slightly better, during the test drive after doing this i really provoked the car so the rev drops would occur, it still dipped but it only dipped below the 500rpm-line once and didn't stall once. I think i have to drive more to know if it's placebo or not but it felt better.

Do you still own the car? Its been a while since the last post.
I also have 95' 328 and with the same problem, i'll try to shut that vacuum line to the exhaust flap and see what happens.

[TeXJ]

Bump, having this issue on an e30 obd1 swapped m52b28 with a m50 intake and aftermarket chip.

I've had it before the intake and chip swap as well.

[E30DEE]

I had this problem last weekend and switched out the o2 with a new one and also changed the plugs and the problem after de clutching disappeared for me.
Here’s the o2 I used if your curious I know some people Are a bit iffy on using certain brands labeled “Bosch” online
https://amzn.to/2JIRFiQ

- - - Updated - - -

I had this problem last weekend and switched out the o2 with a new one and also changed the plugs and the problem after de clutching disappeared for me.
Here’s the o2 I used if your curious I know some people Are a bit iffy on using certain brands labeled “Bosch” online
https://amzn.to/2JIRFiQ

[TeXJ]

I've changed the O2 sensor and the plugs.