Stutter at slow speeds
05-06-2005, 01:09 AM
#21
Member
I think it can be fixed. If anyone has a plug in diagnostic tool / logger, you can monitor the TPS / MAP / Lambda voltage and see what they are up to. Its not an engine fault, im certain its a sensor issue.
The TPS for example, normally monitors the throttle position in a position of 0-5V (0 being closed 5 being open) if that was affected by heat, which you get at idle, it may send a slightly incorrect signal to the ECU which would confuse the fuelling.
My bet is on the MAP/MAF sensor. The sensor's purpose is to work out the engine load, and via lookup tables in the ECU, they work out a correct fuel value to be injecte. These calculate the airflow going past them and convert them into a voltage, sent to the ECU. If you start getting voltage drops, either through irregular airflow over the sensor, or its slightly out of cal due to heat, or air is too hot then it may be giving too low a value into the ECU and thus not enough fuel This would cause the mr skippy effect.
lambda may also be an issus as this also has input into the ECU to ensure the fuelling dictated by the MAP, is correct.
I suggest that if the cooler air from a CAI is helping the problem, its a MAP issue. Must also be a heat issue, as mine only does it after being in traffic a while...
MB
The TPS for example, normally monitors the throttle position in a position of 0-5V (0 being closed 5 being open) if that was affected by heat, which you get at idle, it may send a slightly incorrect signal to the ECU which would confuse the fuelling.
My bet is on the MAP/MAF sensor. The sensor's purpose is to work out the engine load, and via lookup tables in the ECU, they work out a correct fuel value to be injecte. These calculate the airflow going past them and convert them into a voltage, sent to the ECU. If you start getting voltage drops, either through irregular airflow over the sensor, or its slightly out of cal due to heat, or air is too hot then it may be giving too low a value into the ECU and thus not enough fuel This would cause the mr skippy effect.
lambda may also be an issus as this also has input into the ECU to ensure the fuelling dictated by the MAP, is correct.
I suggest that if the cooler air from a CAI is helping the problem, its a MAP issue. Must also be a heat issue, as mine only does it after being in traffic a while...
MB
05-06-2005, 09:06 AM
#23
Originally Posted by Dark Blue Mark,May 6 2005, 10:09 AM
I think it can be fixed. If anyone has a plug in diagnostic tool / logger, you can monitor the TPS / MAP / Lambda voltage and see what they are up to. Its not an engine fault, im certain its a sensor issue.
The TPS for example, normally monitors the throttle position in a position of 0-5V (0 being closed 5 being open) if that was affected by heat, which you get at idle, it may send a slightly incorrect signal to the ECU which would confuse the fuelling.
My bet is on the MAP/MAF sensor. The sensor's purpose is to work out the engine load, and via lookup tables in the ECU, they work out a correct fuel value to be injecte. These calculate the airflow going past them and convert them into a voltage, sent to the ECU. If you start getting voltage drops, either through irregular airflow over the sensor, or its slightly out of cal due to heat, or air is too hot then it may be giving too low a value into the ECU and thus not enough fuel This would cause the mr skippy effect.
lambda may also be an issus as this also has input into the ECU to ensure the fuelling dictated by the MAP, is correct.
I suggest that if the cooler air from a CAI is helping the problem, its a MAP issue. Must also be a heat issue, as mine only does it after being in traffic a while...
MB
The TPS for example, normally monitors the throttle position in a position of 0-5V (0 being closed 5 being open) if that was affected by heat, which you get at idle, it may send a slightly incorrect signal to the ECU which would confuse the fuelling.
My bet is on the MAP/MAF sensor. The sensor's purpose is to work out the engine load, and via lookup tables in the ECU, they work out a correct fuel value to be injecte. These calculate the airflow going past them and convert them into a voltage, sent to the ECU. If you start getting voltage drops, either through irregular airflow over the sensor, or its slightly out of cal due to heat, or air is too hot then it may be giving too low a value into the ECU and thus not enough fuel This would cause the mr skippy effect.
lambda may also be an issus as this also has input into the ECU to ensure the fuelling dictated by the MAP, is correct.
I suggest that if the cooler air from a CAI is helping the problem, its a MAP issue. Must also be a heat issue, as mine only does it after being in traffic a while...
MB
Your analysis is pretty much spot on!
Taking off the MAP & twatting it with a hammer seems to alleviate the problem for a while.
It seems as if the MAP gets crap in the air inlet tube, or something.
I shall keep doing it until I break it! They're ~
05-06-2005, 10:37 AM
#24
Member
Thanks Nick, im using Impreza experience so glad its pretty much the same under the lid! So you've found replacing the MAP cures it? Good stuff, will give it a go when mine gets really bad! 
Id beware of hammering it though, bearing in mind it governs the fuelling. If you bugger it up it may affect the output and cause the engine to run lean. You may not know about til its too late! Thousands of scoobs have blown up from MAF (not MAP but same principle) failure, from vibration due to induction kit installation.
MB
Id beware of hammering it though, bearing in mind it governs the fuelling. If you bugger it up it may affect the output and cause the engine to run lean. You may not know about til its too late! Thousands of scoobs have blown up from MAF (not MAP but same principle) failure, from vibration due to induction kit installation.
MB
05-06-2005, 10:38 AM
#25
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Replacing the MAP? My car's been doing this since new, and it's now about 7 months (although it might be a bit worse now) old (Sept 1st), would they fail that quickly 
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