Uneven at idle and low revs

[blue62]

[QUOTE=DrRobin;643444]

Originally Posted by blue62

I am running on a stock air filter, it was just changed, but didn't make any real difference.

I measured my MAF voltage today, in fact I measured it several times as the engine warmed up at idle.

Ignition on, engine off MAF = 1.008V

Engine on, fully warm MAF = 1.400V, RPM = 793, MAF 4.2g/s (15Kg/Hr)
The short term fuel trims on both banks were around -4%, slightly more negative on Bank 1.

I took readings as it warmed up, once the fast idle had stopped, as follows:

MAF=1.490V, RPM=857, MAF=5.2g/s
MAF=1.475V, RPM=836, MAF=5.1g/s
MAF=1.450V, RPM=806, MAF=5.0g/s

These are lower air flow than I saw a couple of days ago (6.5g/s at idle), not sure how much it changes with temperature, but it is a lot colder here today.

I appear to be just in spec (1.2 - 1.5V at idle) and 13 - 15Kg/Hr, but at the high end and given that my fuel trim still shows the engine as running rich should I still suspect the MAF?

Unfortunately my 5 point security Torx didn't turn up today, so I haven't had chance to remove the MAF for checking/cleaning, perhaps tomorrow it will be here.

I fully charged the battery yesterday between the two tests, with it sitting on the drive, opening and closing the hood and not driving the battery was a little low, not enough to cause any starting problems. Not sure if the battery charge level from 15% to 95% would make any difference?

Robin

Your voltage numbers look ok.
But you stated in post #6 that the engine runs much better with the MAF unplugged.
That makes me suspect the MAF as the issue. Cleaning it may help. At the least you can clean it and see if anything changes.
You could do a vacuum test as vacuum issues can cause your problem. But improved running with the MAF unplugged points to a MAF issue.

The MAF is really two sensors in one unit. "Intake Air Temp". is measured by the MAF as part of it's function. Look at intake air temp when at idle and see if the reading looks reasonable.

Low battery voltage has a huge affect on modern day cars.
When ever your doing any tests or having any issues always make sure basic's like battery voltage is at spec.
Also that battery connections are clean and tight.
That is a first step item in any diagnostic procedure.