Bogging with initial throttle tip in - The Unofficial BMW M5 Messageboard (m5board.com)

getbent · 17th August 2010, 20:44

Car started showing some weird symptoms this am. ANY acceleration with even moderate accelerator pressure results in a split second hesitation and then way more throttle than anticipated. It happens with the sport mode on and off. The best way to describe it is (if you've ever tried this at home) would be say you start accelerating with the sport mode off, then switch it on while holding the gas steady. If you've ever tried that you can feel the engine switch over to the sport mode throttle mapping and get a little punch of acceleration. Problem is this was happening all the time. Almost like a mini-turbo lag, but made it nearly impossible to drive smoothly.

There are no codes displayed. Recent maintenance;

- New plugs over the weekend (doubt this is the issue as the old plugs didn't look too bad - will post pictures tonight- and if anything the idle is marginally smoother plus no mis-fire codes)
- Fuel filter, air filters & oil/filter change 1,000 miles ago
- New pre-cat O2 sensors 500 miles ago (had a b2 & b3 codes, but gone now)
- Thermostat 1,000 miles

Any thoughts on what else to check? Only other random code I've had past month was E8 for the evap valve, but hasn't come back since cleared.

Thanks

OC e39r · 17th August 2010, 21:04

If you are not used to using the sports mode on all the time then I can say you are not pressing firmly on the gas pedal or you are pressing too soon before the clutch is fully engaged. Meaning your foot is hesitant,not the car. Turn off the sports mode and serif it gets better

getbent · 17th August 2010, 21:08

I happens in both sport mode and normal mode. It also happens while cruising - say tooling around at 35 and press on the gas, initial hesitation and then bam accelerates. I've owned the car since new (has 55k on it) and never had something like this before.

Forgot to mention, but did the MAF test and was getting readings of around 138-141 just shy of redline.

OC e39r · 17th August 2010, 21:09

Maybe bad gas?

getbent · 17th August 2010, 21:56

Sorry, you set that up too well. I'm down to 1/2 tank and will try a different station once get down a little more.

OC e39r · 17th August 2010, 22:00

Add some injector cleaner When you fill her up and let's know what happened.

M5 London · 18th August 2010, 01:23

Just a hunch, but check all the wiring on the coils you recently removed and refitted.

I believe one or more coils can misbehave slightly without triggering a cylinder misfire code.

I could be totally wrong of course too.

g9s8r · 18th August 2010, 02:54

Maybe recheck the gapping?

DouglasABaker · 18th August 2010, 03:59

You might try disconnecting the battery (which will reset the DME). You've changed enough of the sensors, but not all of them, that the DME may need to adapt to the new inputs. Or you could just go ahead and change all the rest of the sensors

absolutepressure · 18th August 2010, 05:18

Hmm. It sounds like a sensor response issue. After the car accelerates does it do so smoothly? If so, I'd say either the throttle pedal potentiometer and/or the tps sensors are not accurately relaying their true position. Could be a dead spot at low throttle positions in either. I don't know how often/if the potentiometer goes bad, but I know that the tps's are replaced by many people. One other question, did this issue happen right after doing any other work on the car, or some drastic weather change? When you replaced your sensors, maybe one was only half clicked in.