what causes very small slight miss in rpm range at 2k?

[90mustangfan]

Whether its cold or full temp, I get a small miss/pop out the exhaust at around 1800-2000rpms, its a very small odd pop out the exhaust and the car will studder for a 10th of a sec on that little miss/odd pop in the exhaust and it kinda hesitates... and it doesnt do this all the time but pretty often. timming is 11*, it recently had a full tune up, wires, cap, spark plug, 1 month ago
I get no codes in koeo, and get 31 in cm, which sometimes the cel comes on from code 31 every now and then. would that cause a very slight miss at 2k rpms pretty often?

 

[Jaswir]

put spout connector back in?

 

[90mustangfan]

Yea it plugged in. I cleaned The maf and that helped, but didnt totally remove the small miss, i also cleaned the Air filter, which hasnt been cleaned for 3 year when the previous owner had the car. I cleaned the filter and wow, it felt like I gained 15 horse, the car pull hard and had great throttle response. Im amazed. any ideas about the miss? It does it alittle at idle too. when cold.

 

[91 HATCH]

burnt valves will cause a similar miss to this

 

[jrichker]

TRy clocking the MAF. Clocking the MAF is useful when you have a cold air kit or some other modification to the air box or air inlet before the MAF.

Clocking is turning the MAF housing so that the sensor element is in a different position. It changes the airflow through the MAF to place the sensor pickup in the place where the airflow is the least disturbed. Turn the MAF housing in 45 degree increments to see if it makes a difference.

 

[HISSIN50]

Did you have the issue before the new wires?

I would want to deal with Code 31. You might want to PM Jtfairlane. He went through an exhaustive diagnostic crusade to remedy a mildly similar situation. In short, tell us what your closed EVR voltage is. If above 0.50V, I would pursue this.

Good luck.

 

[84streetstang]

I have almost identical problem, but it only does it when its cold or semi warm, i think it has something to do with it being a carbed motor, i have been a ford mechanic for three years but sadly i am not very smart on carbed motors. Any help would be great,, THANKS!!