Buick Riviera Tune Up

[Adam]

Yes to Tech II.

It's not just a Hitachi MAP (which is just an insert into the throttle body), the throttle body has 'Hitachi' in the casting.

[Bob]

The previous owner told me the car "just had a tune up". Turns out that wasn't really true.

I plan to use this line when I sell the Rondo with its one new coil.

[Adam]

I think the VQ30DE used a Hitachi MAF. I could check. It's in my basement.

You could use the Tech 2 to see if that roughness is registering as misfires. I guess it doesn't have to be ignition. It does sound vaguely like IAC type issues though. The actuator could be a little tired and less responsive than ideal. Could look at commanded vs actual IAC values during that type of transient event and see how well it keeps up.

Does it look like this?

[Adam]

Got the harness. It actually attaches all the vacuum things: MAP, manifold, Fuel Pressure Regulator, and bypass valve control solenoid. It attaches roughly in this orientation looking from the front of the car.

I also replaces the vacuum hoses to and from the bypass valve as they looked to be original and in poor condition.

Tech 2 time! The unit supports IAC testing via commanding idle RPMs in 25 RPM increments starting at 1000rpm. I moved it up and down several hundred RPMs and the response was quick and consistent across all increments.

Misfires are still an issue when in reverse:

Seems to be affecting every cylinder. If you watch IAC performance during the misfires you can see the commanded steps moving all over the place to keep the engine running (idle RPMs were actually moving around quite a bit). Because of this and the IAC test earlier, I am fairly confident the IAC is performing correctly.

The misfire is not present in drive or park. I decided to let it run for a minute or so in reverse and finally got a trouble code:

Mystery solved? I don't have a spare one of these, so I decided to clean it with some MAF cleaner spray. MAF sensor shots:

After re-installation, all seems well.

Fun fact: there is an idle speed difference between drive and reverse. Reverse is ~100 rpm higher. That must have provided enough of a difference in airflow where the MAF readings were out of spec enough to cause misfires. Sure, I'll believe that.

Not sure if I trust the MAF. A Delphi is $85 which is suspiciously close to the price of the AC Delco reman. A new AC Delco is $161.

[Adam]

Another fun fact: the forum thumbnail generator/renderer doesn't respect the EXIF "rotated" flag.

[Adam]

MAF code came back. Replacement ordered.

[Adam]

After looking harder at Rock Auto, I can get a Hitachi sensor (listed as OEM) for only $68, so I've ordered that.