Dirty Throttle body?

[Mike WW]

02, 525ita. Runs well, no codes, vanos has been done, O2 sensors are middle aged, 55K, but not old. CCV and related hoses were done not too long ago.

Frequently when taking off abruptly from a stop, like jabbing the pedal to the floor to get into brisk traffic, it pauses briefly before it does anything. It doesn't die, but more like I hadn't touched the pedal. Half a second, maybe a full one but I doubt it in spite of how long it feels, but a definite gap. Like I hadn't just romped on the gas pedal in spite of the fact that I did. Obviously the car is not a dragster, but it's the response I'm looking at, not the power. I haven't really looked into it, but given the drive by wire I was thinking it might be a sticky TB causing the problem. Any thoughts?

[edjack]

Clean it and report back.

[Mike WW]

Clean it and report back.

Clean it and report back. Really. That's as good as you can come up with? Ed, normally you're one of a relative few here whose posts I put some credence in, but this was saying nothing, just do whatever you think it might be, and tell us what happened. While I'm looking for feedback, if you don't have a clue, don't bother to post. []End of lecture. [/]

[Santaclaus4]

Clean it and report back. Really. That's as good as you can come up with? While I'm looking for feedback, if you don't have a clue, don't bother to post. []End of lecture. [/]

Someone's crabby...
When you say there are no "codes", do you mean there is no "check engine" light? Many things can be starting to fail but not turn on the CEL. Have you connected a BMW specific diagnostic tool such as INPA, etc. Cleaning the throttle body may help but I doubt it's the cause of momentary hesitation when "stomping on the gas pedal".
It's NOT the fuel filter. Before anyone suggests it...
A clogged fuel filter will initially cause power to "fall flat" at high RPM and get worse as the clog restricts fuel flow.
If you had a scan tool of some sort plugged in to the OBD port, you could see what the fuel mixture does and what the fuel trims are. That could be an indication that you will soon get the CEL.

[Mike WW]

Someone's crabby...
When you say there are no "codes", do you mean there is no "check engine" light? Many things can be starting to fail but not turn on the CEL. Have you connected a BMW specific diagnostic tool such as INPA, etc. Cleaning the throttle body may help but I doubt it's the cause of momentary hesitation when "stomping on the gas pedal".
It's NOT the fuel filter. Before anyone suggests it...
A clogged fuel filter will initially cause power to "fall flat" at high RPM and get worse as the clog restricts fuel flow.
If you had a scan tool of some sort plugged in to the OBD port, you could see what the fuel mixture does and what the fuel trims are. That could be an indication that you will soon get the CEL.

No, I don't think I'm particularly crabby, I just thought it was a useless post, unlike yours.

I do appreciate your post and I emphatically agree with the fuel filter observations, I see it referenced so often and especially at idle for instance it's not going to be a problem. I was referring to a CEL, but I did have a scanner hooked up recently and I don't think I saw any engine codes, chassis yes, engine no, but I should revisit.

[Santaclaus4]

I'm not familiar with the 525 so I don't know if it's drive by wire. If it is, maybe the throttle butterfly is slow to respond. If it responds normally, do you hear "intake honk" like you floored it but it doesn't accelerate? Running lean momentarily can cause your symptoms but I'd think it would turn on the CEL unless it's so momentary that the computer doesn't register it as a fault (yet).

[Mike WW]

It is a drive by wire which is why I'm speculating that it might be binding a little bit and the DBW motor might take a moment to overcome it. No intake honk, but remember it's the emasculated I6, not one of the better ones. I'm pretty careful but I have been in there so a quick look at the intake boots/clamps makes sense. It only occurs after a foot off the pedal closed throttle condition transitioning to a WOT, it does not occur if say I stab it on the freeway.

[MIKYZZ4]

Have you tried to reset throttle adaptations?

[effduration]

Just took a DBW gas pedal (from an '03 530i auto) apart to remove the kickdown clicker as part of my ongoing manual swap. These pedals have potentiometers in them I believe (please correct me if wrong). I don't recall people discussing a problem with the pots in the gas pedal, but in your case, would it be worth trying another used one from a junkyard to see if it is any different? Removal is pretty easy.

[Mike WW]

Probably asking the obvious now but couldn't the TB plate be gummed up and opening slowly?

That's what I'm wondering but also if others have had the problem. Not that big a deal, but no fun to get in there, but if nobody else has had the problem I figure I'm not likely to either.

[edjack]

Clean it and report back. Really. That's as good as you can come up with? Ed, normally you're one of a relative few here whose posts I put some credence in, but this was saying nothing, just do whatever you think it might be, and tell us what happened. While I'm looking for feedback, if you don't have a clue, don't bother to post. []End of lecture. [/]

You were the one who proposed it. I was merely reinforcing your observation. Geez!

[R Shaffner]

What about the coil packs? That's a typical symptom when they start going bad.

Gas is actually a poor conductor of electricity. (That's why it's safe for BMW and others to put electric fuel pumps inside gas tanks.) When you hop on the throttle at low rpm, the mixture is temporarily made richer. That makes it harder for a failing coil pack to produce a good spark. The car will stumble and pause for a few seconds before the mixture returns to normal and the engine recovers and responds.

If it's been a long time since the coil packs have been replaced, you might consider replacing the set. (Cheaper as a set.) However, they probably have not all gone bad at the same time. Often I've bought 1 or 2 packs and systematically swapped/replaced them until the car ran better, which meant I'd replaced one or more of the bad coil packs.

If you have a manual, as I do, I usually notice when I open the throttle wide open in a higher gear at low rpm. When the engine stumbles instead of giving immediate positive response, that's my clue that one of more coil packs need to be replaced.

[Santaclaus4]

What about the coil packs? That's a typical symptom when they start going bad.
If you have a manual, as I do, I usually notice when I open the throttle wide open in a higher gear at low rpm. When the engine stumbles instead of giving immediate positive response, that's my clue that one of more coil packs need to be replaced.

Good point. I notice the same when my coils start to fail.
I didn't think to ask if the car seems to "shudder" briefly at low RPM when pushing the accelerator pedal. A just beginning to fail ignition coil will be just barely noticeable at first, usually at around 1,000 RPM and eventually at higher RPM. It won't even turn on the Check Engine Light at first.

[Mike WW]

Good point. I notice the same when my coils start to fail.
I didn't think to ask if the car seems to "shudder" briefly at low RPM when pushing the accelerator pedal. A just beginning to fail ignition coil will be just barely noticeable at first, usually at around 1,000 RPM and eventually at higher RPM. It won't even turn on the Check Engine Light at first.

No shudder. It's more like I didn't do anything, such as push on the pedal, for a brief, but very (to me) noticeable moment. Once it goes it does so with as much vigor as a 4000 pound (with 2 passengers) car with a 2.5 pushing it around ever does. No issues at high RPM or any other time except that transition between idle and large or WOT throttle openings.

[R Shaffner]

It might not be the coil packs, but that's what I notice when mine are starting to go bad. (Hesitation or stumble for a second right after opening the throttle.)

[geargrinder]

Mike yep sure its worth looking at the TB and checking to see if its sticky. If you stumble on "don't work the throttle plate by hand!!!" warnings ignore them, that's horsepoop. Check it out.

Re: the pots, both the TB and the pedal itself on these motors have dual pots inside them for redundancy. The ECU/DMEs have pretty heavy constant validation between the 2 pots in each device, so in both cases they are particularly good at diagnosing failing pots in them (the V8 is even more sensitive - perhaps too much so - in detecting TB pot problems...) so...

If theres any issues emerging w/ either one, then you almost always will have some codes.

As ALWAYS - GG lecture mode - and especially in case of these devices - scanning w/ a BMW code reader like INPA is highly advised because you'll get more and better info.

FWIW the Germanic abbreviations in the proper BMW code text are going to be "DK" = throttle body, and I think "PWG" = pedal.

Both devices are completely separately monitored (not wired together, only linked via software activations...) so the codes will be very specific to the device. For a hesitation, I wouldn't expect the pedal to do that honestly. More like a physical TB stickyness, or, as others have suggested, something entirely different... poor ignition, poor fuel pressure... some kind of other issue like poor mixture causing momentary hesitation...

And no - "No CEL" doesn't mean sh17 for whether there are codes or not. A lot of codes have a preset threshold for how may occurrences or how long through how many starts they have to be around to activate a light so you can have a buncha codes without one.

[BimmerBreaker]

Very unlikely to be the pedal, they are very sensitive, and if it is even a little out of the region it expects it will trigger an EML light.

Since its an electronic throttle body I dont think its a matter of being "gummed up" or dirty. The electric motor doesn't care, it will very aggressively rotate to whatever % position it needs to be in based on the DME output (which determines that output from the pedal sensor). The TB motors are fast and strong, on cable driven cars you can feel a dirty TB in the pedal, and may have to press harder to move it. Thats not the case here.

You should investigate for small vacuum leaks, I'd start with a smoke test. If its not a vacuum leak, may be a fuel supply issue or ignition. I have seen failed coils present symptoms like this before, but usually paired with a slight waver at idle as well.

[Santaclaus4]

FWIW, when my throttle body failed a couple years ago, it didn't turn on the CEL. I got the several warning lights related to stability control and a text warning on the display "ENGINE FAILSAFE PROG".

[geargrinder]

FWIW, when my throttle body failed a couple years ago, it didn't turn on the CEL. I got the several warning lights related to stability control and a text warning on the display "ENGINE FAILSAFE PROG".

Yep that's the typical. Although it might have had a no-CEL code hiding behind there just before you started having "FAILSAFE" incidents.

FWIW, turning on ignition and letting it sit for 30secs then off again recalibrates the TB, and can maybe possibly long shot be a no-hands way to get past the FAILSAFE crisis if you're stuck someplace. If you're having pre-fatal-FAILSAFE symptoms, a few WOTs a la "Italian Tune-up" style can stave off the inevitable for a while. Worst case if you're stranded w/ a FAILSAFE, opening the hood and pumping the TB plate (duh engine off) a few times full-travel will usually get you back on the road for a while. I post this all the time but its alwasy worth reminding in case somebody gets stuck. The I6's have a harder time of it getting to the throttle plate than the V8's but I'd assume same applies (tho' they don't seem to have the problem that we do, which is one reason I conclude the M62TU TB diagnosis is excessively sensitive...)

[R Shaffner]

No shudder. It's more like I didn't do anything, such as push on the pedal, for a brief, but very (to me) noticeable moment. Once it goes it does so with as much vigor as a 4000 pound (with 2 passengers) car with a 2.5 pushing it around ever does. No issues at high RPM or any other time except that transition between idle and large or WOT throttle openings.

Many good suggestions made above.

Question for clarification: You said it only happened when going from idle to WOT (or close to it). Are you sure? Not trying to challenge you, I'm just wondering if other scenarios might shed more light on this.

For example, I suggest you try putting the car in manual mode and first gear, giving it part throttle until it gets to 1500-2000 rpm and then punching it to WOT. (In other words, you'd be trying it not from idle and not from a closed throttle.) If you get a similar hesitation, then I still think the coil packs should be checked. If you don't get any hesitation, then it makes more sense to look at what's going on with the TB from the idle range (like sticking in that range).

One more point: Used TBs are often pretty cheap on eBay and it's an easy swap. You could get one and try it. If it doesn't help, you could probably re-sell it on eBay for about the same price.

[Mike WW]

Many good suggestions made above.

Question for clarification: You said it only happened when going from idle to WOT (or close to it). Are you sure? Not trying to challenge you, I'm just wondering if other scenarios might shed more light on this.


No, not 100%, but pretty sure. It's my wife's car and I don't drive it a whole lot, but I'm a pretty analytical sort.

[R Shaffner]

No, not 100%, but pretty sure. It's my wife's car and I don't drive it a whole lot, but I'm a pretty analytical sort.

Sorry -- my fault for poor phrasing.

I meant: If you floor-it from a slightly faster engine speed, with the throttle in a more-open position, it might hesitate or it might not. If it doesn't hesitate, I'd keep looking at the TB. If it does, I'd examine the coil packs.

(And wow! You have had a lot of old Bimmers. I used to covet the Bavaria and the 2.8 CS -- loved that generation of cars.)

[philly98540]

As stated already, can you get a proper BMS scanner and check for any and all codes?

[BimmerBreaker]

Sorry -- my fault for poor phrasing.

I meant: If you floor-it from a slightly faster engine speed, with the throttle in a more-open position, it might hesitate or it might not. If it doesn't hesitate, I'd keep looking at the TB. If it does, I'd examine the coil packs.

(And wow! You have had a lot of old Bimmers. I used to covet the Bavaria and the 2.8 CS -- loved that generation of cars.)

I have two bavarias for sale right now... ;)