Hi guys new here and wondering if anybody has any advice as I'm pulling my hair out! 

Problem is I have Audi a4 Avant 2.0TDI 170 has been running faultlessly for 2 years. Taken a.over Europe etc.

Coming home from Cornwall last week sat at 70 for 4 hours in cruise control on the motorway running fine untill I left then lost all power under 1500rpm. Thought  i was in the  wrong gear so carried on. Same on every junction! Managed to get it home barely (20miles or so) 

Thougt it would be a quick fix but am I wrong. 

Symptoms... very slow acceleration, it like massive turbo lag uptill 1500rpm then takes off. This is throughout the gears.  Starts ok when warm but cold start takes a few goes and idles rough but then it's fine and idles perfect untill you pull away and it's dead. Have to ride the clutch together going and anticipate each gear shift and drop it down. 

So far I've cleaned MAF, no good so replaced for new one. Same.

Changed fuel filter. Same.

Stripped and cleaned EGR. Same.

Replaced EGR. Same. 

Stripped and cleaned intake manifold and cleaned up swirlflaps checked to see if working on vacumn. Same.

Replaced Boost pressure sensor as when unplugged its running ok just has the glow plug light on. Same. 

Changed it again for genuine Bosch sensor. Same.

Checked wires and connectors on MAF, EGR map sensor. Seem ok. Same.

Had it plugged in numerous times only fault code that shows is P0113 intake air temperature signal too high and P0238 boost pressure sensor signal too high hence changing MAF and Map sensor.

Clear codes runs the same with no faults showing untill we start unplugging again.

Had the AA come out. No idea ! 1 guy said EGR cooler but couldn't back up why and it's a big job to take on with no faults. Had one go on my caddy van and went into limp mode with code so had no issue in changing. 

I've spoke to countless garages and mechanics and it's stumped them all and they are all saying they can't help and would only do what ive already done. As no known faults show up apart form them 2 and the sensors have already been changed. 

Pulling my hair out now and I haven't got much left ! Is there anything you guys no of for me to check before I go insane ? I've ran some live data on OBD 11 and everything seems fine. I'm no expert but everything seems to be ok and In the parameters needed. 

Any help would be much appreciated before I start stripping and changing more parts to find the issue. 

Kind regards 

Andrew

 

Hi Andrew, I've had a similar problem twice now, but I'm pretty sure both times were caused by over revving (stereo on, talking to wife, going a bit mutton) when joining a dual carriageway and pushing too hard in 4th so I'm wondering if this is a possibility in your case? First time I nursed it home about 20 miles as I had the kids in the car and didn't want to risk not being able to restart the car after stopping. Symptoms were basically no power like you, but even at higher revs, it felt exactly as if someone had removed the turbo. the water temp, oil pressure and temp were all normal and no smoke from exhaust so I took the chance and got home ok. Had something to eat and let the car cool down then went to investigate, no oil or water loss, so I tried starting the car and everything was fine. Second time a couple of months later the same thing happened but this time I pulled over at the first chance, turned off the ignition and started it again pretty much straightaway and again the problem was gone. Obviously this hasn't worked for you but the problem sounds so similar I'd be interested to know if you cure it as I feel it's only a matter of time before it happens again. Good luck with fixing it mate.

Dave

Andrew/Dave.

Both problems sound very like limp mode, which can happen without any warning lamps lighting up.

Cheers buddy. Mine has been like it since it first happened. I drove about 150 miles countless resets and still the same. I've just stripped the EGR cooler today in the hopes a good clean would resolve but still nothing. Checked all vacumn hoses and solenoids they seem ok so onto next job. 

My ambient temp sensor has been on the blink since I had the car 2 years ago. Goes from-20 to 40+ depending on its mood but has never gave me any issues as thought that it just controls the A/C but after some research today maybe its telling the IAT its too cold so the ECU is altering the air/fuel mixture. Maybe wrong  but trying everything. 

If I ever find the reason I will.make the whole Audi community know about it as it seems like a common issue but with so many variables on what can cause the sames symptoms. 

Any others ideas or knowledge I'm all ears. 

 

5 minutes ago, cliffcoggin said:

Andrew/Dave.

Both problems sound very like limp mode, which can happen without any warning lamps lighting up.

I feel the same. Its like something is telling the car not to not accelerate but after 1500rpm runs fine.  

The fact that when the the MAP sensor is unplugged its ok is making me think communication from the MAF/IAT is out. 

Trying to get as much info possible before I dig any deeper on parts.

46 minutes ago, cliffcoggin said:

Andrew/Dave.

Both problems sound very like limp mode, which can happen without any warning lamps lighting up.

I was thinking the same, it just seemed strange that each time after turning off the ignition and restarting the car (after about 30 minutes the first time but straightaway the second time) the problem went away. I'm wondering if it's a sticky wastegate actuator that I pushed too far by over revving it? I haven't got a code reader so unless it happens regularly I'm going to wait until my MOT in a month or two and get the guy to have a look then. He's an old friend so if the car's in the workshop anyway he usually has a look at things like that for free as he'll be getting the job anyway if there's anything to do.

It could well be the wastegate and maybe its become free. 

Mine juts happened with no prior warning at all or symptons.

I've got an OBD 11 reader and it's pretty good to be fair it allows you cycle through everything and watch live data so may be worth you getting one.

Ive had 3 garages  plug mine in and it always the same fault but as I've changed the MAF and MAP they are stumped and basically refused to look into it anymore ! 

Fingers crossed it doesn't happen for you again. A good "Italian Tune Up" may of fixed it 😀  

Ive got to the point where I just want to find it regardless of cost. Then I can move forward. Its had the recall on the injectors and loom so hoping it's not them. 

I did and still kind of think maybe contaminated fuel has blocked up pump or injectors. Going down the rabbit hole though thinking of anything and everything ! 

Each time it's happened it's been straight after an unintentional "Italian Tune Up" so I'm avoiding over revving it for the time being. It's more Driving Miss Daisy than Fast And Furious at the moment mate!

I very rarely drive mine like that anymore 😂 I'm too busy looking at the fuel. 

Well I've spent all morning checking the intercooler system and all the hoses and they seem ok. Reset ECM and changed ambient temp sensor and still the same. 

Waiting for my cousin to come and check the electric side of things incase there is a split wire or bad earth so fingers crossed he finds something. 

Update on the A4 and its still the same. Cleared all the faults related to MAF, MAP drove it around this week and they still haven't came back. No faults on the car from 3 different readers.

Just took it to a DPF specialist to check that and it's fine. Seems like it's regening ok so didn't want to force one. 

Boost pressure still looks fine. Everyone seems stumped ! 

Quick question if anyone can help when replacing MAF and MAP do I need to programme it to car? No options on OBD eleven to do this. 

Pulling my hair out now.

Another fault I did noticed was the SAS sensor (can't remember the code) cleared it and yet still hasn't came back. Was wondering if this could restrict power on low RPM?

Also another thing could the cruise control be at fault? Could it also be restricting the power and RPM or ESP? 

Any tips or advice much appreciated before i start stripping the entire engine out 

1 hour ago, Coyney said:

Any tips or advice much appreciated before i start stripping the entire engine out 

Yes. Get the battery professionally tested on deep discharge equipment. A dying battery can cause limp mode to come and go. If a new battery is needed it is essential to get it coded to the car.

Hi cheers. I had new battery 6 months ago and it's been running ok till recently. 

I'll have it checked again.

How do I code it to the car? Is it something I can do? 

Thanks 

Was that new battery coded to the car? It needed to be.

VCDS or equivalent can do the coding. I don't know about cheaper code readers.

No it wasn't coded I didn't realise it needed to be. I'll ask around and see if anyone local can code it for me. 

I've also fitted new MAP, MAF and EGR I take it they will need coding aswell ? 

2 hours ago, Coyney said:

I've also fitted new MAP, MAF and EGR I take it they will need coding aswell ? 

Possibly, but I am not certain.

Update on car as it may help others in the same situation. 

Just took it for a good thrashing with fresh fuel down the motorway.  DPF light came on so thought I'd try clear it. Usually goes within 15 minutes at 2500rpm yet this time stayed on for 30 mins at least. Gave it some welly off the slip road and boom started running fine with low rpm now back to how it was. DPF light still on so carried on but can't get it too clear. 

The car was intermittent going good to bad throughout this (approx 60mins) found when I floored it it would pick up again yet DPF light still wouldn't clear.

Got home plugged it in and the readings are as follows in picture. Now I had garage check the DPF and they said it was fine and didn't need a forced regen yet OBD eleven is saying max capacity at 60% yet mine is high 70's. Not too clued up on DPF's but could this be an issue of loss of power and would it be intermittent? Going to get my local DPF cleaner to look at it tomorrow. No other known faults showing so hoping uts a case of a clean or delete and job done. Will keep you posted 

Thought I'd drop an update just incase it helps anyone else in the future. 

Final cause was the DPF. Wasn't showing any fault codes but was blocked solid. 

 

New DPF and temp sensor, a good Italian tune up to blow all the !Removed! out of exhaust and it seems good for now. 

Will keep updating but as far as now its 100% DPF.  

Current cost is £1250 with a the parts I've fitted so fingers crossed its good for a few years yet.  

But I've just won a mk2 golf gti with an r32 conversion so if anyone wants a A4 BRD tdi with 130k it may be up for sale soon.

Edited September 18, 2025Sep 18 by Coyney

3 hours ago, Coyney said:

Thought I'd drop an update just incase it helps anyone else in the future. 

Final cause was the DPF. Wasn't showing any fault codes but was blocked solid. 

 

New DPF and temp sensor, a good Italian tune up to blow all the !Removed! out of exhaust and it seems good for now. 

Will keep updating but as far as now its 100% DPF.  

Current cost is £1250 with a the parts I've fitted so fingers crossed its good for a few years yet.  

But I've just won a mk2 golf gti with an r32 conversion so if anyone wants a A4 BRD tdi with 130k it may be up for sale soon.

Hi I have come across this problem a lot, most garages only check the soot levels, what about the ASH thats the killer as it can't be burnt off as its like carbon bricks which can only come out the way it went in so therefore your OBD reader was bang on with the high sevens, that was the ASH, I had this when I worked on a Q3 recently soot was fine up to a point but the ash was at 55%, had the DPF professionally cleaned [off car] reinstalled it with a new MAF/MAP and DPF Pressure sensor and EGT, now been perfect for the last couple of months, soot calculated never more than 20g, soot measured after a regen -4g and ash at 1.8g. All good for another 140k.

Steve.

Thanks for the reply and it's nice to hear a different opinion on the issue. Deep down I've always thought it may be the DPF but the readings were OK from what I've been told by garages etc. 

I will now be able to monitor the levels at least as I have a measurement to go by.

I'm more disappointed in the fact that 5 garages which 1 of them was Audi and 2 specialists that they never even considered the DPF. 

I just hope other Audi owners will see this and it will help them to find a cure. 

I'm currently 1250 deep resolving this. The DPF was 270 and labour 355 with new sensor. Can be done on the drive but never had to option to drop the sub frame. 

I hope this helps people have the confidence to tackle jobs themselves. Alot of Garage's now im my eyes are "fitters" not mechanics or engineers. To get refused work due to rusty bolts on a DPF is a give away that your in the wrong place ! 

Will keep everyone updated but as of now running better than ever ! 

 

Well back to square one ! Lasted 1 week! Same symptoms as before, DPF light came on after 1 week and wouldnt clear. 

Had a specialist look at it and found that thermostat was toast so changed that aswell as exhaust temp sensor as that was reading 1800 degrees. 

Took it for a drive afterwards and it regened straight away so happy with that but still same issue with lack of power under 1500rpm.

Pulling my hair out now and ready to throw the towel in. 

If anyone knows of someone in the west Midlands who are clued up im all ears! 

Morning guys,new on here,have a very similar issue with my 170,only difference is my mine has egr and dpf delete.did anyone ever get the bottom of the issue at hand?kind regards Tony 

3 hours ago, Roland rat said:

Morning guys,new on here,have a very similar issue with my 170,only difference is my mine has egr and dpf delete.did anyone ever get the bottom of the issue at hand?kind regards Tony 

Hi buddy yeah i finally found the issue i after changing everything that could possibly of caused it i started looking more into the kive data and found that it was the sensor before turbo in the exhaust manifold. 

It was reading 1000 degrees when cold. 

Put a new one in from Darkside Development and it started back up with no issues. 

Hope this helps mate. Took me 5 months to fix it. 

Hi mate, cheers for the info. I have a very similar problem and it’s driving me mad, done all the usuals like you did and fault is still there.

Can I ask how you checked that sensor please and where abouts is it located? I have no fault codes at all on mine.

any help appreciated.

Thanks

David