A4 1.9 tdi in Limp Home mode after high power.

**saidtheape** · 13-04-2009,11:40 AM

Hi all,
this is my first post, but jfyi I've read through all the available posts on Limp Home relating to the 1.9 tdi, and tried a few things over the last year. I like tinkering, but have limited time, and accept comments/corrections with good grace. Your thoughts are welcome:

Details:
Car:
Audi A4 1.9 tdi 1997, 110bhp variant, old but loved, 218000(!) on the clock.
Modifications:
K&N filter (with oil washed out, MAF sensor regularly checked and spray-cleaned,)
EGR valve bypassed entirely (control pressure hose ends from solenoid blocked and sealed - I figured this was essentially the same as using VAG.com to set the EGR valve to "never open", and would therefore still be within spec - I bypassed the EGR to reduce occasional black smoke emissions when it would cut in heavily rather than smoothly, causing stutter and kangarooing in extremes. I tried swapping out the solenoid and hoses with a known-good unit, to no effect - so I'm 90% certain it's the EGR valve - certainly the smoke and kangarooing stopped as soon as I bypassed it, the occasional Limp Mode symptoms continued without appreciable change).
Emissions at last MOT (with EGR bypass in place, feb '09): 0.49
Oil is changed once every six months with GTX 10w40 religiously, all other checks are done ad-hoc but regularly enough to fall within service specs.
The turbo is allowed to cool after high-speed/power use for the requisite few minutes before shutting off the engine.

Symptoms:
Over the last 3 years the car has gone into Limp Home with increasing frequency, in broadly the same set of conditions. Cycling the ignition resets it 100% of the time, and no warning lights or other(?) indicators are present.
Limp Home occurs particularly when accelerating up motorway hills, usually around 2-2.5krpm in fifth, but if the engine/turbo is required to produce a lot of power under any circumstances, it may happen.
It seems more prone to enter Limp Home in wet weather, or after a large puddle splash.
This was difficult to pin down at first, as I was living in Mid-Wales...
The engine otherwise seems strong (albeit old) and if allowed to get a run up at a hill will happily climb it _at a totally constant throttle setting (not necessarily a constant speed)_ up to the limit of it's rev range. But as soon as you press your right foot down a fraction more, it'll likely go into Limp Home for the rest of the climb.

Visual inspection and finger-pressure jiggling of the turbo bearings reveals no appreciable play (in the words of a decent mechanic who services his own tdi taxis to good effect)

Final clue: after using Kalimex K-Seal to fix a pinhole in the heater matrix and a small leak somewhere very hard to locate in the bottom of the block, the car would power up long hills under full (and variable) throttle without a hint of a limp... but that lasted about a week, and since then it's back to its old tricks.
The engine block coolant leak seems permanently fixed - although the heater matrix pin-hole seems to've returned after a month or two (water vapour in the hot air, great in rain and dark), so I'm going to replace it assuming I can fix the Limp Home problem.

As I said, when it's not limping home it seems strong, and as in all other respects it's a solid old car I'd like to nail this problem down and keep it from being scrapped for a few more years, even if I don't keep it myself.

I think I really need someone with a VAG.com kit to take a ride with me and my laptop, and figure out exactly what the onboard computer thinks is happening when it enters Limp Home. I'm local to west Somerset or southern Hampshire depending on work and time of week, so any offers of help would be appreciated. I can repay in kind with a decent stab at fixing any PC/Mac/Linux problems you've got, my fu is strong in that area.

**Crasher** · 13-04-2009,12:17 PM

Yes, you hit the nail on the head in the last lines, you must get a fault code read done. This could produce quite a few codes and one I would expect to see is “00575 Intake manifold pressure Control difference”. With it probably having been a long time since the car was last scanned and you obviously do a lot of work on the car yourself, I would suggest the initial fault code report is treated with suspicion, it will probably contain a number of what I call “ghost codes”. The best plan is a code read, print and clear and then take it away and drive it for a week and get the fault to reoccur. In the meantime, do not disconnect anything on the engine, especially with the ignition on or it running, this way any codes that come back will be relevant.

**saidtheape** · 13-04-2009,02:59 PM

Thanks for the response Crasher. I see you're in Nottingham and a pro at this stuff - I might well take advantage of your services in the near future, but I'd like to get the first set of readings (at least) locally before heading up north; so I guess my question now boils down to: "Does anyone in Somerset or Hampshire have VAG.com gear and an hour or so to spare, and maybe a strong urge to see the M3/M5 from the passenger seat of an ancient A4?" I should be able to reproduce the fault within a quarter of an hour or so at most.

Thanks again.

**mrjolly** · 15-04-2009,11:21 PM

yo, there will probably be a vnt (variable nozzle turbine ) turbo on your car.
these things can suffer from sticking nozzles which makes the car overboost and puts it into limp mode, check out posts about vnt turbos.
hth sid

**constablechris** · 16-04-2009,01:55 PM

I had the same problem - there is a turbo pipe (sorry for my somewhat nontechnical description...) under the pipe that goes from the air box to the front cold air intake - it was loose on mine, had one of those clips that you screw tighter and it grips more. Tightened it up and hey presto... no more limp home mode!

https://www.vwaudiforum.co.uk/forum/s...ad.php?t=64991

Here is my thread.

**Marc1** · 24-04-2009,09:50 PM

No where nea you mate, but hope you get it sorted. You've clearly put alot into the car, so it would be good to keep it running sweet, passed the 250K mark! Good luck and post any info you get up as it could help others.

**Walesy** · 24-04-2009,11:44 PM

My 110 tdi does this, exactly as described in the original post - I took it to a garage and they found oil in some of the vacume pipes and told me I need to replace the turbo! does this sound reasonable?

**Crasher** · 25-04-2009,10:52 AM

Oil in the vacuum pipes? That is almost impossible, do you mean in the charge air pressure pipes, the big ones of the little ones? Did they do a fault code read? If so, what were the results?