2002 C70 Weird computer reset issue, poor running intermittent

[Sommerfeldt]

So, between incidents, the car runs absolutely great, not running rich, no computer codes just happy Volvoing. I have a friend with a Volvo Junk yard so I have about 4 MAFs I've tried, it idles great so I doubt there is a air leak and there are no O2 sensor codes...

LTF takes a looooong time to change, and I drove for quite some time with a bad O2 sensor w/o codes and intermittent sputtering/black smoke. Reset would take care of it for a week or two. You're right that air leak isn't probably, since an ECU reset wouldn't fix that, and the MAF would be short term fuel trim troubles, mostly. The combo of a bad MAF and bad O2 could definitely result in your issues, with the work you've done, the ETM is probably a better bet.

- S

[abscate]

Just on a whim...more things to check. Go through and remove and inspect every vacuum hose on this car.

I solved a poor cold running problem from a horrible split evap vacuum hose on my 99

[bmdubya1198]

It would be a good idea to look at the O2 sensor signals on an OBD2 reader. That's a basic test just to see that they're doing something.
Vacuum leak is a possibility, but I agree that it seems unlikely due to the problem going away after an ECU reset. But this is Motronic 7, so crazier things have happened. Check the larger diameter vacuum hose that runs under the intake manifold and connects in the center, I think between cylinders 2 and 3. That hose tends to split and create a massive vacuum leak.

When the ETM was bad on my V70R, I don't think I had a code for it either. The ETS light would periodically come on, but no P-codes. I was lucky enough to find a matching white label ETM at the junkyard that has worked perfectly since then.

When the ETM goes all kinds of ugliness happens. Someone here on the forum took my spare ETM for testing and then dropped all communication, ggggrrrrrrr.

I take it that was his problem!

[dobrosailor]

I went over the vacuum lines pretty methodically but I will do them again. Its funny that it always so far starts in the morning when its bitter cold but when it doesn't start, its been after work in the parking lot. I have the hood open with my 10 mm wrench disconnecting the battery at work in 30 degrees. Yesterday it tried to do it but I managed to floor it and clear it out. I bet next time I come out from work it will require a reset. Something is slowly skewing the matrix of settings in the computer. THIS SUCKS!

[dobrosailor]

I went over the vacuum lines pretty methodically but I will do them again. Its funny that it always so far starts in the morning when its bitter cold but when it doesn't start, its been after work in the parking lot. I have the hood open with my 10 mm wrench disconnecting the battery at work in 30 degrees. Yesterday it tried to do it but I managed to floor it and clear it out. I bet next time I come out from work it will require a reset. Something is slowly skewing the matrix of settings in the computer. THIS SUCKS! I have several MAFs that I have tried - no luck.

[abscate]

How does it run with MAF disconnected ?

An ECU reset can definitely “fix” a leak as it will run on lookup table until it generates a new set of parameters

[precopster]

I'm going for a sticking ETM throttle plate. In cold weather the clearances change and you get flap closed upon startup/self-check giving you rich mixture and poor starting.

Resetting battery is the answer because ECM may have calibrated off that stuck flap. It takes 5 minutes for ECM and some other electricals to be denied power with key off on these ETM cars (I've timed it in the workshop)

I had a couple of ETMs through with throttle stop screws that had vibrated out of position. Once you remove the ETM deflect the flap fully home (closed) and see if it sticks. Sometimes there's enough carbon there to cause this. ETM throttle stop screws are located under 2 aluminium plugs on top of the ETM. You can drill out the plugs and adjust them with an allen key without tearing the unit down.

[dobrosailor]

I wish the ETM was easier to get to. I have cleaned it out a couple of years ago, not a fun job! I can check it out again. I usually just disconnect the battery, then hit the starter motor to discharge the capacitors.

[bmdubya1198]

It's definitely not a fun job! Hopefully the hose clamp on that intake hose is positioned for relatively easy access. Otherwise, just pop out the fan, that intake hose, and you should be able to get to the four screws with relative ease.
Make sure you get a new gasket for the ETM too.

[dobrosailor]

Still battling with this one. It has morphed to flooding when I start it sometimes. I can usually catch it and either floor it so it starts or rev it above 2500 till it clears out. I do have one other issue I failed to report. On the highway if I floor it, it goes but not full on and when I lift slowly, there is a point where the car takes off like a cylinder kicked in.

I love this car, is comfortable, rides like a dream, extremely quiet since I plasticwelded the dash mounts back together last weekend but I am getting sick of these ghost issues. Any hope???