Hello all,

Recently I've been having an odd problem that I can't seem to find anywhere, so I figured I'd give the forums a try. It started about 3 weeks ago, after I filled up with gas at a cheap station I hadn't used before. Almost exactly as the remaining gas in the tank was used (I was having a little fun that day) on a pull entering a highway my car removed all power from the throttle and held the transmission between 500-1500 rpms while slowing. Luckily I was able to pull off, but without ever stopping the car (or engine) control was returned to the throttle with a CEL. The transmission also returned to normal. The code read as a P0087 code (fuel rail or system pressure too low), so I tried some system cleaner and the light went away that day.

Since then, sometimes when I get on the highway and usually when it goes past 4000rpms around 60-70+ mph, the throttle loses input control, the transmission upshifts once or twice, and the check engine light comes back before returning complete control to me. This happens more obviously in sport mode (since it keeps it in the power band ie breaking 4000), but has begun to affect comfort mode as well. The codes go away after 2-3 more drives (recentness does not matter) and it still preforms fine on taking off, though I haven't pushed it like I used to since I haven't figured out the problem yet. My innova 5110 (and autozones) code reader only detect P0087, with varying amounts of the code being clearable and one permanent one. My friend has a Youcanic which could measure the fuel pressure, and his dad has the xentry platform at home, though theyre going to the GAT show for the week so it'll be a minute before I can get their help. I'm also unsure as to how much knowing the pressue value will help in troubleshooting.

Has anyone else had this issue after using a different gas supplier? I used 93 but I think the ethanol content may have been too high, however i'm 2 more tanks of confirmed good gas and 2 tanks of fuel system cleaner in and the problem persists. I haven't ruled out a sensor issue (ive seen the other thread about an e550 with a similar issue), but I have never gotten any supporting codes with the P0087 to help clarify like they did. I still drive it daily, but I want the racecar side of it to work as well as the commuter side so I'd like to figure something out .

 

Update 1:

it seemed like it went away when I got below half a tank of gas, but upon refueling the issue arose when entering onto a highway. I'm going to try replacing the sparkplugs soon since they are due anyway and it might be that one got too dirty or something. Otherwise I'm still stumped. For a short while after the light comes on (and continuing after it goes off) the car seems hesitant to downshift like it normally wants to, but I cannot figure a correlation to anything on when this goes away. I know the shifts are based on some kind of average, so maybe thats part "safe" mode part me being easier on it. There are still no supporting codes for the issue, only P0087. The car also has trouble starting (starter still cranks like hell and power turns on fine) ONLY when parked facing downhill. It hasn't failed to start on me yet, just takes longer than usual. How all of this could be correlated is truly beyond me, but the car is fine otherwise so it can remain that way for now. Any input or ideas are welcome, and I'll update once new plugs are in on whether than worked or not.

 

Didn't end up putting in the new plugs, but the light seems to be mostly benign at this point. It'll just flash on sometimes now and I'm able to do 5-6k rpm pulls no problem. My friend thinks its the computers wanting me to go to the dealer and get it cleared, so next time we use xentry on it I'll update on how it develops. Also verified that it is not the high pressure pump, as it had no issues at highway speeds this last weekend even with the light already on. Also, does anyone have any advice when I do have to change the plugs? we got the coil undone but the boot wouldn't come out easy so we gave up before we ripped anything, and will be sidelining it until I get the money for new boots/coils just in case.

 

Xentry didn't do anything the cheap OBD didn't besides clearing the perm code. Going to try replacing the fuel pump soon since our theory is the filter is just getting clogged from years of misuse and my slip up was the straw to break the camels back. I did buy it with a fuel pump code so it's not impossible. Any advice is appreciated.

 

Update: still happens

I'm pretty sure it's the bosch temperature sensor like this thread found https://mbworld.org/forums/e-class-w...m_content=post
It only occurs when the car is "suprised" and needs to downshift, and the issue can be entirely bypassed by manual mode. I have no idea why this is, but it makes highway drives more enjoyable anyway, so I just downshift to pass now. I have a theory that it might also be due to exhaust modifications (along with the once a year downstream bank 2 o2 sensor code) from removing my resonators and having old cats. Will update once I get around to buying the sensor.