idle misfire gone when unplug MAF
 

so i have a misfire at idle and my mpg has dropped from about 17-18 to 14-15 for the last 2 tank fulls..when i unplug the mass air flow sensor it dissapears and idles smooth. tried driving like this but it shifted way too hard..

i have cleaned the MAF and checked for vacuum leaks but couldnt find any.. the smoke test did show that the idle air control and egr valve leak but from what i could find these are vented to the atmosphere.. i sprayed both with carb cleaner and even tried propane while the engine was running to detect a change in idle but turned up nothing..

going to check and see plug condition and do a compression test and see if that turns up anything..

anyone have any thoughts or experience with this situation? maybe theres a common problem im unaware of i should be checking out?

Re: idle misfire gone when unplug MAF
 

what did you use to clean the MAF? im willing to bet the MAF is bad

Re: idle misfire gone when unplug MAF
 

i notice you have kn air filter, did you give it a fresh oil cleaning in the last while? if so you could have an oil film on/in the MAF.

Re: idle misfire gone when unplug MAF
 

i used maf cleaner made by CNC and yes i just got the K&N filter about a month ago and oiled at that time.. the MAF looked like new but i cleaned it anway since then..

from my understanding even though the misfire goes away when i unplug the MAF, thats just showing that the MAF IS working and that the problem is somewhere else.. i would think its an air/fuel issue and not ignition because unplugging the MAF wouldnt effect an ignition issue and the misfire would still be there.. i think..

i get what sounds like a vacuum leak sometimes when at idle in gear once the car is warm but can not find it.. i have tried spraying every where with carb cleaner and did the smoke test but nothing.. maybe the sound of fluid running through a line somewhere sounds like a whistle? seems to be coming from under the truck near bell housing/engine area..

heres a video of the whistle.. around 30 sec is when you can hear it..

Re: idle misfire gone when unplug MAF
 

i would like to know how you kept your motor running by unplugging the maf? i was trying this today and it would run for about 30 seconds then dies. i took off the plastic intake that goes to the throttle body to get more air in... still couldn't keep the engine running. mine is 90tm.

Re: idle misfire gone when unplug MAF
 

i just unplugged the sensor where it connects to the air filter housing.. it idled fine and i drove it to the store but shifted harder than a mofo.. so bad i felt like the tranny was gona break so i plulled over and plugged it back in after about 1/2 mi of driving.. this is a 97 4.0 ohv