1999 XC70 Rough Idle and Acceleration Hesitation

[El Cheapo]

Hello,

I've had an intermittent rough idle and hesitation on acceleration. New coils and spark plugs were recently installed, and a quick check of the ETM doesn't look like the problem. So I've turned my attention to the MAF sensor. Decided to provide a photo + voltage measurements taken with a voltmeter (key on; engine off) to aid in the diagnosis:

Connector Position # /Wire Color/ Voltage
#2 /Green / Orange/ - 11 V
#3 (looks like “3PT” in photo) /Brown / White/ - 0 V
#4 /Purple / White/ - 5 V
#5 /Green/ - 1 V

If wire #3 is the MAF signal, it looks like my MAF sensor is bad. Without a wiring diagram, it isn’t clear which wires represent input power and ground circuits, but I am getting positive readings for the other wires.

Before I spend $100+ on a new MAF sensor, does anyone know which wire is #3?

Thanks

[El Cheapo]

Update: Identified which wires are responsible for which functions based on a Bosch diagram. MAF checked out okay with the multi-meter.

Started the wagon today, and the rough idle returned. While in park, the MAF sensor reading was a bit higher (1.95 V) than when the idle was smooth (1.45 V) and did not increase much (2.05 V max) while revving the engine. However, despite putting the pedal to the floor, tachometer did not go above 2,500 rpms. (At one point, I actually recorded the MAF sensor reading @ 0V at idle, but now it's consistently at ~1.9 V.)

I've cleaned the throttle body and checked a few other easy things. Now my attention is on the ETM. Even though it has the replacement "yellow sticker" on it, it doesn't mean it hasn't gone bad again. Originally with the key 'on' and the engine 'off', I could hear the familiar click on and whine of the ETM. After 6 seconds, it shut off as expected with the key still on. However, when the rough idle condition returned today, I could not hear the ETM click on with the key 'on' and the engine 'off'.

Much has been posted about the relationship between the MAF and the ETM. But it's still hard to discern whether the poor MAF sensor readings are a result of the ETM malfunctioning or a failing MAF sensor, since a defective MAF can produce similar symptoms as the ETM.

Before I remove the ETM and spend $$$ at XeMODeX, are there other things we can rule out to confirm the real issue is with the ETM? At the same time, I hate to spend $$ on a new MAF sensor if it's working fine.

Thanks!

[chuffs]

I saw on another post that the ETM requires min. 12.5 volts--it sounds as if you may have already checked the connections and full length-disconnected resistance of: positive and negative battery-fuse box (Saw green powder and broken strands down in my fuse box on wire for positive lug in fuse box)-body/grnds and to TPS. Youtuber showed how to stab the rear of TPS connector and verify variable voltage outputs from (on his) .5-5 volts (closed-open)..Let us know what you find. Good luck.

[chuffs]

Try............http://vexedvolvo.org/ this link has extensive troubleshooting info for ETM