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E34 525i Tourer M50 Engine. Light throttle drag at low or cruising speed

2K views 3 replies 2 participants last post by  dongiov 
#1 ·
Owned car virtually from new, done 177k miles, engine superb. Symptom started sporadically 2K ago with sudden surge of revs at idle and engine cutting out after long runs when car coming to rest. Always instantly started, symptoms would disappear for awhile. Got worse with changing ICV, since replaced FPR & fuel pump, MAF, Lambda, & temp sensors, fuel filter, cam sensor, checked ECU and all hoses & manifold for leaks, vanos solenoid, run Wyns fuel system cleaner. No faults come up with engine diagnostic scan, and have now eliminated rev surge and any stalling, but still light throttle drag at low or cruising speed - almost like a flat spot; but car pulls like a train through rev range on open throttle. At MOT last week, exhaust emmissions were bang on. Totally baffled, any thoughts much appreciated. Thanks
 
#2 ·
Max,

you checked all hoses for leaks but given the age of the car, I would change the lot over it is all old and as in some places, if you have a leak, it is not easily detectable. I have a 1992 525iX and some of the hoses were perished yet looked ok. For instance, the fuel regulator hose just fell apart when touched. Its not expensive but in my case helped bring the engine back to good condition and may solve your problem for not a lot of money. in doing this you will also have to take the manifold off so change those seals as well.

Alternatively as it is light throttle drag, check out the whole accelerator pedal/bowden cable assembly. Again, at 177K, womething may have worn out.

Hope this helps

Geoff
 
#3 ·
Thanks Geoff
Sorry to take an age to respond. I did replace a whole host of hoses and whatever I did never made any difference and worse the symptoms started to vary, with diagnostics giving haywire readings all over the place. I got so fed up that I was about to scrap the car, when I took a closer look at the non original new replacement MAF sensor I installed. I got this item from a well known after market supplier, so did not question its integrity to work - but when I compared it to the OEM item - it looked diabolical, the electronics if you can call them that had blobs of solder on the sensor filament, and its casing was made of muck metal and crude plastic. My pals at Quarry Motors came to the rescue and sent a good OEM s/h one - and bingo the car runs great. I have learnt a very very expensive lesson here - never ever fit anything peripheral to a BMW engine management system that is not OEM. !
 
#4 ·
HI Max,

that makes sense, I bought a E34 525i vanos tourer that had failed its MOT three times on emissions, the previous owner had changed the MAF over for a cheap aftermarket version in an attempt to get it through the MOT. I swopped the MAF with a good original one from another car, changed over a broken vac hose, replaced the spark plugs, ran Cataclean through and hey presto, it passed. The cheap aftermarket versions are not good enough.
 
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