Messing with the MAP
 

Screwed up my courage, got the Gastester fired up, got the car good and warm. Pried the plastic cover off the MAP, stuck a 4 mm hex key in the adjuster with the handle sticking up.

Brought the RPM up to 3000 and observed 1.2% CO. Went more than 1/8 but less than 1/4 turn to the right, and the CO came up to about 3.2%. Backed it off a bit, and dicked around with calibration and retesting, and I think I got it pretty close to 2%.

The good news was that this brought the idle CO up to slightly over 6%, so I was able to back off 4-5 clicks on the ECU to bring it down to 2%. Engine is sounding much healthier at this point. Felt good on a test drive, except for a lumpy idle in gear and a bit of stumbling under light load.

So I went through another cycle of reading the CO and calibrating the sniffer. What seemed to be happening is that the MAP/ECU are not compensating quite enough for for the load in gear, and the a lean miss occurs. I finally ended up up screwing the idle air mixture screw down about half a turn with the car idling in gear. Bizarrely enough, this did not lower the in-gear idle, but did smooth it out. This sort of makes sense, because by reducing the air, you are in effect richening the mix.

So now I have a decent idle in gear, but a lumpy idle in P/N. This is not great but OK because most time is spent in gear. My next step is to mess with this, but to buy or try to beg/borrow a better sniffer to get more exact readings.

All this went down Friday afternoon. Today the car went in harms way on a typical Saturday circuit - down the GW Parkway (for running), into Arlington (for latte's), a few miles on I-66, and a stop at the garden center (rather large plant). Lots of stop and go. No problems except for the P/N idle, and a light miss under acceleration while it was first warming up.

So, more tinkering with the idle mix, and checking out the coolant sensor to see if it's doing its job during warm-up driving.

One think I don't recall seeing in scanning this thread, is much about the AAV (aux air valve). These things are prone to sticking. I have had mine out a few times. I have cleaned it with solvent, detergent and even ultrasonic. I had to squeeze the bulb slightly to get it to close at about 190F. I think it is still slow to move when cold.

Even with engine close to operating temperature (170F), squeezing the line between the AAV** and the idle valve cause the engine idle speed to slow showing air is passing through. After a good run, this is no longer the case, showing the valve eventually closed even although temperature is only slightly higher.

**I bought a new hose from Performance - it is not as hard as the original and quite easy to squeeze.

The AAV can be a large air leak!

Another one can be the vac advance line - I found I was not getting any vac advance - Mityvac showed diaphragm was leaking. Not much though.

End of the story
 

This thread is continued here:

http://www.peachparts.com/shopforum/vintage-mercedes-forum/222154-cant-get-d-jet-run-right-2%25-co.html