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help :-(

7K views 33 replies 11 participants last post by  OURMANDAN 
#1 ·
been trying to find the dreaded cause of P0174 & P0171 codes.

I have tried

Cleaning maf (looks pretty new anyways)
Checked disa and is working properly and o-ring looks good
Checked intake boots for cracks/holes etc...
Checked for leaks with spray and listened for engine changes.
Checked cover gasket and seems new and not brittle

The car drives fine and if i clear the codes and only drive about town they don't come back, but when i drive over 30 miles in one go they come back

I also have a P1620 code which is thermostat but seem to be working fine, could this be a cause of the other two codes or am i being silly?

The car is also weird as when i floor it from cold (i know its bad) it doesn't move like it should, until it is up to full temp and even at that the low end doesn't pick up quick like it should it just bogs down till over 3k revs

Anything i could now try would be a great help as it is starting to drive me insane trying to solve it :)
 
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#2 ·
The P0171/174 codes are classic intake leak indicators. I bet the 2 large hoses need to be replaced, along with the "F" connector on the upper hose. Your best bet is to have the intake smoke tested. The other code indicates that the thermostat is failing. As a result the engine never reaches its proper operating temperature of between 95*C and 100*C. This can be verified by using the dash's hidden functions. Google "E46 hidden OBC functions." Test 7 will show the engine temperature that the ECU sees.
 
#12 ·
How do you know the thermostat is working properly?

See the first 3 links in my signature.

If the MAF looks new, it may be a counterfeit Asian unit.
 
#14 ·
I dont know if this helps any but you can see from the image below i have a pretty high long term fuel trim is this a good indication of a vacum leak? i tried a smoke test tonight quickyl as it is driving me insane, but couldnt see any thing where it could be leaking. Im going to have to try get a real smoke machine and do it properly.

 
#15 ·
You really need to give the LTFT with a fully warmed up engine. According to your screenshot the coolant temp is 52C.
 
#17 ·
When doing the smoke test and pushing in smoke through the intake boots, right after the MAF. The way I see it; the smoke has nowhere to go on the M54 when the engine is shut off. Both the ICV and the Throttle Body are fully closed with the engine off. Pushing in smoke that way will tell you if your intake boots are leaky and thats about it. If you have an old M54 with a cable throttle you can pull it to open it, but for those of us with an electronic throttle - there has got to be another way of pushing in smoke. prehaps through one of the capped off vacuum ports on the back side of the intake manifold, facing the driver.
 
#19 ·
this just doesn't seem to be the case as there should still be air able to get through as the throttle will be shut in idle and the engine still needs air to idle through small channel which is regulated by the icv or I may be wrong and the icv shuts fully when the engine is off but this didn't happen in my case and smoke did pass through but then again that wasn't an actual machine smoke :)
 
#27 · (Edited)
I think the ICV remains partially open when the engine is off. The very end of your video showed that.

You can use the vacuum line from the purge valve for smoke test. I test several inlets including CCV hoses, dipstick tube, PS booster hose, intake, etc.

Someone should do a proper smoke test DIY with photos or video. I haven't seen a good one for M54 yet.
 
#28 ·
I knew it did remain open a tiny bit but was completely starting to doubt myself :)

I was thinking about the dipstick and would it work, I might try it from there actually later on and see how it goes, just need to find the right size hose to try it with
 
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