Throttle body or throttle pedal problem?

[hedges88]

Been trying to get to the cause of some odd fuel trims on my Mercedes-Benz W169 which I've already posted about. I've performed every guided test with XENTRY/DAS and it passes them all with flying colours, except for WOT driving. There is always a few items found to be out of tolerance, ignition angle, throttle position and kickdown switch. I don't expect to have a kickdown switch as I have a manual but was puzzled by the other findings.

Using Torque Pro and an ELM scanner through my head unit, if I press my foot to the floor the throttle position only goes to 87% or so. I've noticed pressing very hard on the pedal it increases. If I literally push the pedal as hard as I can (some creaking can be felt) the TPS goes to over 90%

I seem to therefore have found the culprit, I'm failing my WOT test because quite simply, I'm not at WOT!

I performed a throttle body reset/valve stop reset through DAS, nothing has changed. What is likely to be the problem here, the throttle body itself or the pedal? No error codes of any kind for anything. I know the TB is clean I had it gleaming only a few hundred miles ago when I had to replace my spark plug leads, and therefore being a W169 had to strip some of the engine bay. I did have new injectors fitted by a garage not long ago which improved my fuel trim situation a bit but they still are erratic at times and I can feel/hear something is not 100% with the engines operation.

TB should be under warranty as was replaced by garage not long ago, and pedal units I've seen for as little as £9 so either way I'm not worried about a big bill just don't know what to do or try first

Answers on a postcard please

[GreenV8S]

Have you triedr moving the floor mat aside?

[hedges88]

GreenV8S said:

Have you triedr moving the floor mat aside?

Good shout but zero obstructions

[E-bmw]

Many BMs have an adjustable pedal stop, have you looked closely under/around pedal in case there is one?

[stevieturbo]

hedges88 said:

Using Torque Pro and an ELM scanner through my head unit, if I press my foot to the floor the throttle position only goes to 87% or so. I've noticed pressing very hard on the pedal it increases. If I literally push the pedal as hard as I can (some creaking can be felt) the TPS goes to over 90%

I would not be trusting anything on generic apps like that. They're a toy, not a proper diagnostic tool. And often generic OBD data on such tools is just wrong.

Get proper info and if it is DBW, ensure blade position is matching target, largely ignore what the pedal says

[hedges88]

stevieturbo said:

I would not be trusting anything on generic apps like that. They're a toy, not a proper diagnostic tool. And often generic OBD data on such tools is just wrong.

Get proper info and if it is DBW, ensure blade position is matching target, largely ignore what the pedal says

Your right, I should just use the BT ELM scanner for general reference on the head unit, ie a toy and use something else for proper diagnosis. I have done some things such as disabling fuel calculations to make what's displayed quicker and more reliable. Mercedes own DAS software does not even show fuel trim information for example so it's all I've been going on until now.

It is drive by wire. If we went by the garbage BT ELM and Torque Pro for those figures then I have Throttle Position, Manifold, and absolute throttle to choose from its the pedal position one that im seeing.

If I get an actual handheld scanner that I just need for more reliable information over OBD would something like this be okay for personal use, or too cheap?:

https://www.ebay.co.uk/itm/313704651398?mkcid=16&a...

[E-bmw]

hedges88 said:

If I get an actual handheld scanner that I just need for more reliable information over OBD would something like this be okay for personal use, or too cheap?:

https://www.ebay.co.uk/itm/313704651398?mkcid=16&a...

It will be netter than nothing but as it only does engine you may well find an all systems one for your car a better bet.

I haven't read the full spec, but perhaps something like this.

https://www.ebay.co.uk/itm/313582736793?epid=19013...

Or this, I had one of these but BMW specific & it was quite effective.

https://www.ebay.co.uk/itm/192657616793?epid=80337...

[Belle427]

Finding out some specs to test resistances etc would be helpful.
Not sure how else your going to find out.

[hedges88]

So I'm past needing the scanner stage now. I get in the car this morning and feel something is a little off, give a little rev and the exhaust is popping and banging. I look at the exhaust and can see fuel vapour curling over the chrome of the exit tip. This is obviously the open loop stage as engine is just started, but I l know this is a symptom of excess fuel. I take it out for a drive to monitor what goes on under closed loop (despite my basic scanning setup). Rear catalyst temp is very high for urban driving, STFT keeps going negative 5/10/15% but LTFT is jumping to positive 8/10/12%. Then I'm noticing during the drive every time i change gear there's an audible sigh from the engine, only when I've let off completely as i change gear I can't reproduce the sound by suddenly on/off throttle whilst in gear.

I take it to the A6 for an uphill stretch I often use because with so little power I can keep on WOT for a little bit without breaking the law. At WOT STFT is absolute zero and LTFT is positive by about 3.9%. When back into the town the figures start jumping all over the place again, catalyst temps have fallen but catalyst 2 remains a little high.

I do my best to do a makeshift smoke machine with my vape, quite a vast quantity of vapour but still not a smoke machine standard. I'm noticing it clinging as if being pulled around the middle of the VLIM pipes where the top long runners and bottom short runners meet. Could be a hairline fracture in the plastic from age or heat? I've attached an image so you'll see where I'm talking about.

I can change that plastic unit if it is the problem, but i need to know for sure. Rang 3 garages so far that don't have a smoke generator or thinking I want my emissions checked Is there anyone in the Bedfordshire area I can entrust this too please? I don't want to keep driving it like this because of the catalyst. Any decent little garage or workshop will do, or even a car enthusiast willing to help out for beer tokens.

[rottenegg]

Is your engine Direct injected?

My MK5 GTI behaved like that when a couple of it's DI injectors started going bad.

[hedges88]

rottenegg said:

Is your engine Direct injected?

My MK5 GTI behaved like that when a couple of it's DI injectors started going bad.

No it's MPI delivered by injectors mounted on a rail. The injectors got replaced when I first started having problems, not cheap but I thought they might as well need doing anyways. Didn't solve the problems.

I've just replaced the MAP with the official BOSCH part after noticing the one that was mounted was aftermarket. No difference. I thought maybe a hairline crack somewhere in the VLIM because of the way I saw my vape smoke clinging around there but I think it's just the shape and indentations that cause it to happen. I got convinced the VLIM box was damaged due to what I perceived as plastic moulding being chipped off on the leading edge of where the short/long paths meet but after having a look at various examples on eBay they do just seem to vary in their moulded shape.

I've rung so many garages that have basically said "you've done everything we would do anyway". I guess they don't like I have DAS and have been able to test everything myself.

I just don't know where is good to take it to that specialises in these sorts of advanced vehicle diagnostics. Could be a bad oxygen sensor, small vacuum leak.....I just don't know

One thing I know is that STFT goes crazy high at low throttle/low load situations like where your not quite on the overrun but getting there.

Drives me mad. Might have to embrace the butthurt and allow MB to deal with it......

[rottenegg]

Yeah that is the danger of taking it somewhere when you've already invested so much time into it yourself, but you cling onto the hope they'll spot something you didn't!

Is the engine MAP only, or MAF as well? I've seen fake MAF sensors under reporting air mass at low load/rpm causing exactly that behaviour also.

[hedges88]

rottenegg said:

Yeah that is the danger of taking it somewhere when you've already invested so much time into it yourself, but you cling onto the hope they'll spot something you didn't!

Is the engine MAP only, or MAF as well? I've seen fake MAF sensors under reporting air mass at low load/rpm causing exactly that behaviour also.

No it's MAP only. I did have a suggestion from a friend today that the massive spike in fuel trim at low throttle could be because the electronic throttle is not at the correct position. That's been replaced once and the replacement has been reset now a few times while trying to fix this problem. If you ask DAS to move it to a certain degree it reports back it is at the expected position

I have to do my A service in 26 days and while I'm happy to do it myself I've noticed a strong smell of fuel when opening the oil filler. It was like that last service I did as well though the oil drained from the sump didn't have a petrol smell, you only seem to smell it through the filler neck.

Head gasket test passes just fine, compression test via DAS is okay. I think the engine itself is okay. Just something along the lines of air, fuel or spark gone wrong somewhere, so you know just about every single thing a petrol engine operates by

No error codes to go by, no obvious reasons. Hard to know if the fact it runs fine at WOT is a confirmation of a vacuum leak or because it goes back to open loop due to engine load so that does not rule anything out for me unfortunately.

I need somewhere to take it that's good with reading and analysing sensor logs and that can perform a vacuum test with a smoke generator etc but I haven't found anywhere.