Quote:
Originally Posted by maytag
Start with the easy stuff first.
Lumpy idle can very frequently be traced to the MAF. ESPECIALLY when, as you describe, it's fine when cold. But when the motor warms and it kicks out of the pre-programmed cold start settings and starts using sensors to determine settings then it gets rough..... yeah.... in my world that points to MAF all day long.
AND it's easy to check. When your idle gets rough, unplug your MAF and see if it smooths back out.
Always easy stuff first.
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Unplugging your MAF senor to check MAF sensor condition is not a very reliable test of the MAF sensor.
Yes it seems to work if your sensor is bad.
But by unplugging it your not really testing it.
What if you have a vacuum leak?
A vacuum leak can cause lumpy idle, it is a lean condition due to the unmetered air.
When you unplug the MAF the DME reverts to a default fueling strategy based mostly on engine load and RPM.
That default fueling strategy is biased on the rich side which tends to compensate for the lean condition so the car idles and runs rather well with a vacuum leak and the MAF unplugged.
Plug the MAF back in or replace it now the car again idles lumpy because in this case it was a vacuum leak.
So now in this case you have spent what? over $200.00 on a new MAF sensor and not fixed the lumpy idle.
Much more reliable ways to test the MAF.
Fuel trims and comparing Throttle Position Sensor signal to MAF sensor signal are two means.
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