my m42 has developed an annoying issue. idles like shit hot and cold, like 500rpm or so where I have to finesse it to keep her going. In addition to that there is a related problem where while accelerating (at any rpm range, it doesnt matter it seems like) the engine has ignition cut or something for a split second and the car bucks. this bucking problem is MUCH WORSE WITH O2 SENSOR UNPLUGGED sometimes it will do it a few times in a row, other times just once. Both problems developed at same time. For now I cleaned the ICV and found that the vane is seemingly frozen in place. unplugged the ICV and now my hot idle is around 1500 - car is atleast dailyable. If the vane is frozen how can unplugging it change the idle?
fuel pressure tested good. AFM is not even 4 months old and is refurbed straight from BAVREST. TPS tested good, may be a bit out of spec but not bad (ranged from 1.4kohm to 4.3kohm with no hiccups throughout whole range).
car is throwing a cam sensor code CODE 1244, but I swapped out cam sensors between two known good ones and no difference. Unplugging the sensor doesnt change a whole lot.
The oxygen sensor relay I discovered to be bad at this time, not sure how long it has been bad. the sensor itself is right around 2 months old. When checking for the heater circuit's fitness I found 12V at the heater relay pin 87 (to the o2 sensor) only when ignition is on engine running. With the engine not running no power. I assume this is normal however at the oxygen sensor harness I am unable to get 12V power on pin 3, or any of the pins for that matter. I was grounding the negative pin to the strut tower and looking for 12V+ on the male connector of o2 harness.
UPDATE: the coolant temp needs to rise enough for the DME to turn the relay on, and it is pin #4 that is the 12V power. my car checked out fine after it warmed up.
so I found, summarized:
- Fuel pressure read 38psi at idle, up to 45psi under WOT. Responded to changes in vacuum/throttle immediately. this vehicle also has rebuilt 21# injectors and SSSQUID tune to match
- TPS tested good
- coolant temp sensor reading 230ohms once warmed up, not bad right? spec is right around there +/- 10%
- coil packs all ohmed out good. removed the HT leads one by one and the idle changed equally on each cylinder
- engine wont idle with AFM unplugged... so AFM is good I assume, its brand new after all
- unplugged o2 sensor and drove around, problem was much worse. same symptoms just 4X as often, accelerating up hills was painful LOL
- ICV measures out at 8ohms resistance and idle raises significantly when unplugged... the ICV felt frozen when I cleaned it by hand the other day with carb cleaner - so not sure what is really going on.
Additionally, before the engine is warmed up and the cold idle is still struggling (because ICV and o2 were unplugged) opening the oil cap and introducing a large vacuum leak SMOOTHED THE IDLE OUT. There was also loads of air chuffing through the cap. Never seen anything like it before, my guess is that the rings arent sealing so great from running rich and that equates to extra crankcase pressure.
any ideas? Im great with the multimeter so let me know what I should be testing, Im sorta stumped. Im ordering a new oxygen sensor but need to figure out the wiring problem first.
fuel pressure tested good. AFM is not even 4 months old and is refurbed straight from BAVREST. TPS tested good, may be a bit out of spec but not bad (ranged from 1.4kohm to 4.3kohm with no hiccups throughout whole range).
car is throwing a cam sensor code CODE 1244, but I swapped out cam sensors between two known good ones and no difference. Unplugging the sensor doesnt change a whole lot.
The oxygen sensor relay I discovered to be bad at this time, not sure how long it has been bad. the sensor itself is right around 2 months old. When checking for the heater circuit's fitness I found 12V at the heater relay pin 87 (to the o2 sensor) only when ignition is on engine running. With the engine not running no power. I assume this is normal however at the oxygen sensor harness I am unable to get 12V power on pin 3, or any of the pins for that matter. I was grounding the negative pin to the strut tower and looking for 12V+ on the male connector of o2 harness.
UPDATE: the coolant temp needs to rise enough for the DME to turn the relay on, and it is pin #4 that is the 12V power. my car checked out fine after it warmed up.
so I found, summarized:
- Fuel pressure read 38psi at idle, up to 45psi under WOT. Responded to changes in vacuum/throttle immediately. this vehicle also has rebuilt 21# injectors and SSSQUID tune to match
- TPS tested good
- coolant temp sensor reading 230ohms once warmed up, not bad right? spec is right around there +/- 10%
- coil packs all ohmed out good. removed the HT leads one by one and the idle changed equally on each cylinder
- engine wont idle with AFM unplugged... so AFM is good I assume, its brand new after all
- unplugged o2 sensor and drove around, problem was much worse. same symptoms just 4X as often, accelerating up hills was painful LOL
- ICV measures out at 8ohms resistance and idle raises significantly when unplugged... the ICV felt frozen when I cleaned it by hand the other day with carb cleaner - so not sure what is really going on.
Additionally, before the engine is warmed up and the cold idle is still struggling (because ICV and o2 were unplugged) opening the oil cap and introducing a large vacuum leak SMOOTHED THE IDLE OUT. There was also loads of air chuffing through the cap. Never seen anything like it before, my guess is that the rings arent sealing so great from running rich and that equates to extra crankcase pressure.
any ideas? Im great with the multimeter so let me know what I should be testing, Im sorta stumped. Im ordering a new oxygen sensor but need to figure out the wiring problem first.