Better idle with Mass Airflow Sensor unplugged

[Blue2KTA]

I have been chasing down an idle problem and decided to unplug the MAF to see if it would run different and it did idle better (also ran ALOT better). I understand that it stays in open loop while the MAF is unplugged but would that make my idle better ? Is the MAF bad ? The idle problem i'm having is when im at a light (A4) after about 5-7 seconds the idles gets jumpy. Rpm's only vary +- 20 (scantool). I replaced the iac, cleaned the MAF, plugs, wires, checked for vacuum leaks.

[pajeff02]

Have you cleaned your MAF lately? Is it modded in any way -- ie. ported, de-screened or de-bladed?

[Blue2KTA]

Have you cleaned your MAF lately? Is it modded in any way -- ie. ported, de-screened or de-bladed?

I cleaned the MAF with CRC cleaner. MAF has not been modded.

[pajeff02]

It's possible the MAF has an issue. Easiest check would be to swap it with the MAF from a friend's F-body and see if the problem remains or goes away. How about the idle air control valve?

[Blue2KTA]

I have no F-body friends The IAC is new.

[pajeff02]

Did the problem pre-date the new IAC?

[Blue2KTA]

Had the idle problem first, before any new parts.

[0rion]

sounds to me like either a vacuum leak ( did you check the pcv hose?) or unmetered air somewhere. I would recheck everything with a fine tooth comb. What about the small line going to the hvac controls on the back of the manifold? Do your hvac controls work properly? List your mods for me please....at least the mods that matter.

[Blue2KTA]

I replaced the pvc valve and hose that goes to the intake. The hvac is working properly. I checked for vacuum leaks with starter fluid. The car is stock.

[pajeff02]

Well... when you unplug the MAF, the PCM switches over to speed density and calculates airflow using the MAP sensor and engine RPM. I assume the MAF is essentially the same from 2000 to 2002, I can give you the pin point tests for the MAF from my service manual. Do you have a digital voltmeter?

[Blue2KTA]

Yes i do

[pajeff02]

I'll go dig out the manuals here in a bit.

[pajeff02]

I'll start with the plug schematic. I believe the MAF has a full 12 volt signal, rather than the standard sensor 5 volt feed that most everything else runs off of. Check for power on the pink wire and do a continuity test on the black/white wire to ensure that it is properly grounded. Obviously, you will be testing the plug and not the sensor itself and the ignition will need to be in the "run" position. For giggles, also check your "ENG SENS" fuse in your underhood electrical box on the driver side.

[pajeff02]

The MAF sends its signal to the PCM in Hertz, rather than in volts. Therefore, the yellow wire does not have a measurable voltage output. The easiest thing to do is plug in a scanner and watch the MAF's output. Most scanners will convert the data to grams/second of air flow. At idle, you should see in the range of 5 to 9 grams/second and at 2,500 rpm it should be approximately 20-26 grams/second. Note that these measurements are on a stock engine and that mods affecting airflow will most likely result in somewhat higher readings.

[pajeff02]

You can probably perform a continuity test on the sensor as well, although I would thing that your Check Engine light would be on if the circuit was open. On the MAF, with the harness unplugged, check for continuity between the pins for the pink and black/white wires. You should see some resistance as the signal passes through the MAF's wires. If there is no continuity at all that might be an indication that the MAF is in fact broken.

[pajeff02]

The diagnostic info essentially states that if the MAF is not working, or if its signal is too far off from what the PCM thinks it should be (based upon the MAP, IAT, ECT and RPM signals) then a Diagnostic Trouble Code (DTC) should be set. Most common are P0101, P0102 and P0103.

[Blue2KTA]

Thanks for all that info ! ! I hooked up my scanner but it reads the MAF as lb/min instead of grams/second. The reading is .75 lb/min at idle, don't know if thats bad... I posted a video of the log.

[pajeff02]

Well... .75 lbs./min. equals 5.669 grams/second, so the MAF appears to be within spec at idle.

Here is the converter I used: Online-Unit-Converter.com - mass-flow-rate. Mass flow rate.

[Blue2KTA]

I guess the MAF is not causing the problem. Has to be something else that's looked at during closed loop.

[pajeff02]

Since you have the ability to scan, I would watch the MAF output when the car starts to act up.