Hi,
i recently posted on here the problems with my multi 115bhp 2004 model.
Early this morning we should have left to go for 2 weeks camping down South, but car still in limp mode and its got to take my wife, myself and our 4 kiddies, a roofbox and trailer!.

I am going to give a brief outline of symptoms and stuff i have done
(with a lot of valued help from Peat so far).

money is very tight, so not touched a stealer, i would borrow some if i thought dealer could sort it, but from all other posts on here, vast majority of times the dealer takes all your money and rarely gets it right.

Symptons: driving car at 70mph, beep from dash and limp mode, dash saying engine cntrl faulty contact garage.

i have Yanis software and hooking up got error P0236 overboost valve.

i replaced overboost valve with a new one from shop4parts, also noticed the larger red tube that goes down to turbo actuator from boost valve
had hole in it, so repaired this.

Cleared fault with software- symptons came back, car little sluggish, then soon as hit appreox 3000 revs, engine light on & same error code and full limp mode.

Car sounded rougher than it was before fault also, i checked egr and removed, (had cleaned few months prior to clean). egr seems ok, fairly clean still and valve moves freely and actuater side (the pin) moves freely).
noticed crack in lower pipe coming from egr, had it welded up.
car sounds much better, no rough blowing sound, but fault still recurrs.
someone mentioned try MAP sensor,so i ordered & replaced that- still same symptoms.

Actuator at bottom of turbo can be moved nicely if i press it down, but i have not seen it move under revs.

Last night i disconnected MAF sensor and cleared fault, went for run and car drove perfect (no lag at all) until approx 3000 revs and then limp mode (but not as bad as when maf connected).
error codes as expected with maf unplugged- air flow too high, air flow too low, but interestingly the overboost P0236 error was there but in a different state- it now said the error was still present (as with maf connected it always said error was now clear, but stored).

On yanis software i have tested (actuated both egr and overboost valves and they report completed).

Could it be the MAF sensor after all?, i seriously think its at least also faulty, if not the sole cause of my woes.
i gently cleaned the maf, but connected, no difference.

Anyone any ideas?, had similar??.
weather hot & sunny, we should be half way to Devon by now,
going to see if i can get hold of a maf sensor today and if it doesnt cure it, take the chance in limp mode and go tomorrow morning
anyone got any ideas.. seriously would be a lifesaver :worship:
thank you
mark

There seems to be an assumption here (and understandably so) that the fault codes will always pin-point the fault correctly. However, its a bit like treating a headache - the pain might be in the brain but the cause can be something else (eye strain, lack of sleep, too much beer... etc)

The Turbo overboost error is a common fault code, but it has been suggested that this can also show up in error when in fact the problem is that the exhaust as recirculation (EGR) valve is stuck. The EGR valve becomes very sooted up and jams - leading to a reduction in power and can also cause smokey exhaust. Eventually the solenoid that operates valve this can fail (burn out) because of the jammed valve 'shuttle'. The EGR valve can be removed and cleaned, and the solenoid tested (apply 12v to it and see it move). Do both of these before replacing the turbo overboost solenoid. A split or damage to the red vacuum hose between the overboost solenoid (just beside the battery) and the actual turbo valve (on the front of the engine) can also cause the overboost valve fault code to show. Repairing or replacing the pipe will solve this issue (and is much cheaper than the solenoid)

You have repaired the split red hose (so prb didn't need new solenoid -- that controls vacuum applied to that hose, but the o/boost valve will not operate unless vacuum reaches the turbo end), and you say you've cleaned the EGR valve (operated by data from the MAF sensor, by the way). I suggest the EGR solenoid isn't working.

Another possibility could be the vacuum pump (top right hand end of the engine) failing. This supplies the vacuum pressure* that operates the o/boost valve. Also provides the brake servo vacuum -- do the brakes feel soft? Not sure how easy to would be to test this, and again, the slightest hole in any of the vacuum pipework could lead to a loss of vacuum effect.

Hope this helps
Pete

*strictly, it creates negative pressure, causing a suction.