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P0170 P0173 MAF or not to MAF?

11K views 67 replies 10 participants last post by  tml320p 
#1 ·
A happy new year to everyone!

Yesterday, wife's ML 430 (MY 2000, 98k miles) hesitated to accelerate on pressing the gas pedal, eventually CEL turned on and my iCarsoft i980 reader pulled the codes P0170 and P0173. A quick search on this forum suggests that this could be because of a bad MAF or the fuel pump or some leak in the air intake, or the cats, or ...

Today I cleaned the MAF, cleared codes, then took the car our for a ride and, yes, when pressing hard on the gas, the engine doesn't fully rev up. After about 15 minutes it gets worse and the engine sputters and has a rough idle, but when being soft on the gas, it still drives its 30mph, CEL eventually on.

I am wondering if I should replace the MAF before I bring it in to my local indie shop? MAF has last been replaced on 05/14/10 at 62k miles. Air filter is new. Fuel filter has been upgraded and replaced on 09/23/09 at 58k miles.

I have only limited tools and mechanical abilities (I am able to replace the MAF on the ML 430, but, today, I failed to take out the MAF on my w209 for swapping it with the ML :-(). The i980 scanner has live-stream data that might be useful. The attached screenshots are after resetting the car (disconnecting the battery) and idling for a minute or two. I wonder if any of these values would point towards a particular component that should be checked? Before the reset during my clean-the-MAF-and-drive-test I found that intake manifold air pressure and measured airflow by the MAF were increasing/decreasing according to engine RPM (as I would have expected).

I can take more measurements of the streaming data if helpful. I don't have a pressure gauge for measuring fuel pressure, but if someone tells me what to get and how to measure then I am willing to get the equipment. However, if turns out to be the fuel pump (or the cats, or something beyond my abilities), then please don't be disappointed if I take it to the shop.
 

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#2 · (Edited)
It would have been more helpfull if you had not disconnected the battery as your fuel trims have been cleared. I would think its a gross vacuum leak.
check the brake booster hose at the back of the engine. Also remove the plug from the MAF sensor and start the car and see if there is any improvement.
Upload a video onto utube of your scanner with what you have above as these values change as its running.
Short term fuel trims are at max. Oxygen sensors on B1 S1 and B2S1 should bounce up and down around 1-9

Edit I would add though that i have never seen such a high reading of short term trim. I know when you disconnect the battery long term trim is data is deleted so you start again building your long term trim, And your short term trim will go up or down for a while depending on the problem but wow.
 
#3 ·
Thanks megadamp and sorry for leaving this thread dangling.

In short, it was the fuel pump. Everything is back to normal since two weeks after replacing it (I also tried replacing the MAF but it didn't change anything).

To help others, here were the symptoms: 1. Car needs a bit longer for starting. 2. Engine accepts little gas but when pressing more on the pedal it stutters or doesn't rev up.

Some other random notes: my two mechanics independently said that in 90% of the cases of P0170, it is a problem with the MAF, thus checking with a new/other MAF first is still a good idea. Just not this time...
 
#5 ·
See what you all think of this. 1998 ml320, 247000 miles, runs great, shifts great, vibrates at idle in drive, cant tell car is running at idle in neutral, getting codes p0170 and p0173. cel comes on for a few days then goes off for a few days. currently cel is off. any ideas. Thanks
 
#6 ·
Mechanic at dealer told me my my MAF was bad so got a new oem maf from pelican parts. cel was back on in 45 miles with p0170 and p0173. car runs excellent. A couple of months ago i got a code that pointed to o2 sensor bank 2 sensor 1. I replaced that one but none of the 3 others has ever been replaced. Looking for any suggestions as what to try next. Thanks
 
#7 ·
I have now replaced every breather hose including the 5 way unit that connects to the intake manifold and to the top of the throttle body. I also replaced the secondary air injection hose, and the round seal where the intake tube meets the throttle body.
All of these items were extremely brittle and definitely needed replacing.

I am still getting p0170 and p0173.

The intake tube looks perfect no cracks and all clips are in place (not broken). The air box is not clogged and filter is new. All of the monitors reset within 20 miles each time i clear the two codes after new parts are installed attempting to solve un-metered air leak.

Any other ideas would be greatly appreciated. Thanks
 
#11 ·
I found a loose brake booster hose at the back of the manifold. the o-ring had become like plastic so i replaced that and still got codes p0170 and p0173. I have now had the car smoke tested and no vacuum leaks were found. Car runs perfect and is getting 19mpg in town. I have read so many threads on this and none seem to fit my condition and i am at a loss as what to do next.

In the driveway in park if i accelerate from idle to about 4000 rpm the engine is turbine smooth. When it passes 4000 rpm it seems to miss. I do not get any misfire codes. When driving on the highway past 4000 rpm and above the car runs smooth. Don't know if this matters at all but just stating what the car is doing.

Thanks
 
#14 · (Edited)
Do you have means to look at live data stream? There is very simple sanity check for MAF. Put your scanner in grams/second and read air flow. At idle you should see 3.2-3.7 g/s. In second gear with wide open throttle look at air flow just before 2-3 shift. It needs to read .80 of advertised HP. At WOT small vacuum leaks play no role is mixture formation.
 
#15 ·
I do have livestream capability and my MAF is a new oem bosch unit from pelican parts. I am getting 3.63 at idle and around 170.0 at the shift point which is right around .8 of the advertised 215 hp of the vehicle. so assuming MAF is good.

I did get a code p0130 recently but it did not come back. I bought the o2 sensor for it any way and will be putting it in tonight. I read codes when i got home tonight and p0170 and p0173 are in the pending codes again. I am sure the CEL will trigger soon.
 
#19 ·
I meant to add I did get the new 02 sensor installed tonight at the bank 1 sensor 1 location that i got the p0130 code on recently. The fuel trim values are with the new sensor. My O2 sensors status is B1S1 new today, B1S2 original, B2S1 10 weeks old, B2S2 original
 
#20 ·
Sorry to send you on wild goose chase.:frown

All we need is values with key on, engine not running. Better yet values from freeze frame when codes P0170, P0173 have occured.
 
#23 ·
If that engine ever reached 190 C force of exploding radiator would dent the hood.:big laugh:

As far as your problem fuel trim values look normal. My E320 runs with LTFT @10% and has never had CEL on. Normaly LTFT has to climb to 15% before CEL comes on.

Disconnect and plug vacuum hose to EGR valve. Drive it for few days see which direction LTFT moves. Yes, you will get code for EGR flow.
 
#28 ·
Let's wait two more days and see if there is any more movement in LTFT. And of course fault P0170/P0173 coming back. Lazy closing EGR valve may produce same symptoms as large vacuum leak. In fact that's how EGR system gets checked for flow (or lack thereof). During long deceleration valve is deliberately opened and manifold pressure is monitored. If there is no drop in intake manifold pressure fault P0400 is set.
 
#29 ·
I ran vehicle 3 more days without clearing any codes. The codes I have are 400 and 460. 400 is for the plugged egr valve and 460 is for my fuel level sensor. I am not worried about the 460 code because I know the fuel sensor is whacky. When I fill up the guage goes to empty - the next day it reads full and works fine.

The main thing here is, after 3 more days of driving I have not registered any more p0170 or p0173 codes in pending or stored codes.

Are we getting warmer?
 
#30 ·
Any further movement in LTFT?

Replace EGR valve and while you at it clean EGR pipe. When fitting new vacuum hose between EGR valve and nipple on manifold make sure length and routing does not obstruct movement of throttle. In front of intake manifold there are two vacuum hoses that are usually rotten by now. One goes to manifold pressure sensor other to secondary air injection switchover valve. Replace those as well.

P0460 will not trip CEL.
 

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#35 ·
I have left that hose off at least twice.:eek Engine never stumbled. It was not until next day my wife complained about fumes in the garage that made me look closer at her E320.
 
#40 ·
Took ML to the dealer Tuesday and had it smoke tested. It has leaks at the manifold gaskets, the vac hose that comes out of the bottom front of the manifold, and the rubber elbow that connects the resonator tank to the plastic intake tube. Looks like manifold has to come off. Haven't decided if I an going to do it or have dealer do it. They quoted in the neighborhood of $500.00 to do it.
 
#41 ·
For all of that being fixed by an MB dealer using genuine parts that is not a bad price. Plus it would have a nationwide warranty for 12mos/12k miles at any dealer in the country.

Yes it is mostly a labor job, but also one that requires lots of delicate removal of parts with the right size and right kind of tools.

I really am surprised that they quoted the estimate that low.
 
#42 ·
It is not going to end up that easy. Vacuum hose from front of intake manifold to switchover valve is listed but not replaceable. If there is a leak between manifold and cylinder head it is not gasket failure. It is erosion of material from intake manifold. Magnesium from intake manifold just evaporates into thin air leaving big voids behind. Same issue with valve covers.
 
#43 ·
I am not going to screw around with the old intake manifold. The bottom front vacuum hose is hard and leaking vacuum and will continue to be a problem. I took the manifold off myself this morning and really wasn't too bad of a job.

Is a new pierburg manifold ok - the one I took out has a bosch sticker on it.

Any suggestions on where to buy the manifold and gaskets? Seems to be a lot of choices out there.

The dealer has the gaskets fairly cheap.

Are there torque settings for the manifold bolts?

When I removed the fuel rail I noticed the Injector o-rings looked pretty flat and at the tip of the injector there were plastic looking keepers for the bottom o-rings that look like they should be replaced also. Are these keepers a replaceable item.

Thanks
 
#44 ·
Other then front vacuum hose is manifold sealing surface pitted?

Pierburg is OEM it will be fine. Gaskets and injector seals from the dealer.
2x 112 141 20 80
12x 019 997 13 48


Plastic heat shield on injector is not available separate. There is a listing for injector seal kit under Bosch number 1 287 010 704 but heat shield in that kit is wrong.

There is oil port plug in the middle of the V replace it if there are any traces of oil near it.
 

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#47 ·
If sealing surface is good then your only problem is that silly hose in the front. I would check with Brinson on Monday details about that repair kit. In the past solution to this was to dig out all remaining material from that hole and glue new piece of hose with RTV sealant.

I will do some more research about injector heat shields.
 
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