CO Changes?

[heung]

What causes the CO to change other than the CO 4mm adjuster screw? Using the CO meter I have set my 85 Euro 930 to 2% and idle speed to 950 rpm after the engine is warmed up. Next morning, (temp 80 deg F) engine could hardly hold idle after started. Drove out and engine felt lean with back popping sound during deceleration (sign of lean CO) In the afternoon, started the same as the same in the morning, except during traffic crawl, idle speed beginning to creep up and stay at between 1400-1600 rpm. Then at speed, it seem it has the correct CO again. No more popping sound during deceleration. What causes the irregularity?

FYI. Since I have the car the engine has never started like my Merc CIS startup with a high Vroooom upon startup and quickly settled at set idle speed. This car just startup at about 600-700 rpm and then settled at idle speed usually. But it does startup every time.

Cheer.

[mark houghton]

Hmmmm.....The poor low idle at cold start would lead me to think that the enrichment circuit in the WUR isn't working properly (the WUR when cold should reduce the fuel control pressure until the WUR is warmed up by the action of it's internal heating element, in conjunction with the engine temperature)...and it may also mean that the AAR is not fully open when cold.

Your high idle in traffic makes me think that (1) control presssure is too high as controlled by the WUR, thus running too lean, or (2) your AAR is either stuck open or has lost the electrical power that's connected to it (could be a bad connection at the plug, or the rear fuel pump relay - which also controls power to the WUR and AAR). But if you lost power to the WUR as well, then it would begin to cool down and should under normal circumstances cause the mixture to richen up (simulating cold start conditions).

The only way to adequately troubleshoot this is to first check the system and control fuel pressures with the special gauge setup that's needed. If you don't have the gauge, then you may want to try setting your mixture a bit richer at idle (closer to 3%) to see if that helps. These cars all need their own special adjusting, depending on the state of tune and any modifications that have been done. Sometimes there's a little trial and error involved to fine the sweet spot.

Meanwhile, when cold take the hose off the intercooler side of the AAR (auxillary air regulator, assuming the EURO has one) and look inside to see of the disc is showing a full open notch. If fueling is correct, that open notch will let air into the intake and raise the idle.

[heung]

Hi Mark, thanks for your detail comments and sharing your knowledge. Questions, can the WUR and AAR be service? Usually what is the commom things that can go wrong with this 2 piece of parts?

Cheers

[mooney265]

You stated you "set the idle mixture while warm" and "the car still runs fine once warmed up..."

My guess is that your "cold" control pressure is too high, thus causing the lean running while cold... You could check the pressures [there are many write-ups on this] with some CIS gauges.

If your WUR is stock, then you may want to consider an adjustable one...

[heung]

The WUR is stock. What does a adjustable WUR do? Do we adjust the fuel amount or the pressure? Where can I get one and what does it cost? Can the AAR or the stock WUR be serviced?

Cheers

[RarlyL8]

The fuel pressures need to be verified along with the electrical power at both the WUR and AAR. If your engine does not idle high when started cold the AAR may not be operating. Vac leaks should be eleminated as well as they cause many symptoms.
We handle WUR rebuilds and mods if you find yours is worn out and no longer holding spec pressures.