I got one for the knowledgable on the list

Picked up an '88 244 last week, nice condition, but had
a rough idle. Get past idle and drive it and it ran quite well.

Changed the plugs, it was slightly better, but still pretty rough
at idle. Started poking around sites like Brickboard and others,
found it might possibly be things like the AMM or dried up
injector seals.

One message in a forum said if the AMM is faulty, the idle should
smooth out if you unplugged it. I tried that and it was better. So, I went
into my trunk and dug up the AMM from my dearly departed '89 744
and installed it, and the car idles almost perefectly now, BUT it idles
quite a bit higher than normal. Without a tach in this car, I can only guess
at how much - perhap 300 to 400RPM above normal.

I checked some of the online parts sellers for info on the difference
between the original AMM, Bosch p/n 0 280 212 007, and the one out
of my 89 744, Bosch p/n 0 280 212 016. I learned that the '88 has LH 2.2
while the '89 had LH 2.4. This is apparently the reason for the p/n
difference.

Now, the question is, can I continue to use the '89 AMM on this car, without
damaging something over time, and adjust the idle down a little to make it
right? Or is there enough difference between the LH 2.2 & the LH 2.4 that
would rule out continuing to use this one and spending the $$ on the correct
replacement?

I have yet to order a Bentley book for this one, so I would also need info
on
adjusting the idle properly if I can keep the setup as it is...

Thanks...

Dennis
Putnam Co NY

 

I'm not one of the knowledgable (wait for word from Glenn, User or Mike F
before going overboard) but I think your original AMM was bad and the idle
adjustment was turned up to artificially compensate.

With the new AMM, let it idle and look for a knurled knob under the throttle
body. If you find one, turn it clockwise (count the turns) until the idle
stops dropping as you screw it in. If it makes things worse, put it back
where it was. The truly knowledgable can tell you how to adjust it correctly
if I've put you on the right track.

Mike

 

Thank you, Mike - I saw that knob but avoided turning it until I was
sure it was an adjustment knob. I don't want to start undoing everything
before I know just what I'm touching...

and knowledgable is relative - you're a lot more knowledgable than I,
from what I've seen on the list. <G>

Dennis
===============================================

 

Thanks, Dennis - that knob is on the end of a needle valve that controls a
bypass passage around the throttle plate. That passage is also one of the
most troublesome areas of the throttle body when it gets gunked up.

Mike

 

I've often noted on my 240 that idle is very improved after the simple
maintenance of cleaning the gunk from the throttle body. The gunk prevents
the valve from complete return to closed position, allowing too much air
intake at idle and causing a too lean/poor idle condition. Remember to
clean out the pin-point sized valve openings in the throttle body while
you're at it.

If this does not improve your idle, you've only lost about 30 minutes to 1
hour.

While you're at it, remember to clean the flame trap in the nearby vicinity.
I don't know if this can affect idle, but it can affect engine seals, and it
is easy to take care of whenever you do routine maintenance to clean your
throttle body.

 

No, the two AMMs are not compatible. The reason your car is idling better
is because it's idling at 3000 RPM. I'd start checking for some big
vacuum leaks.

 

No the MAF Sensors are not interchangeable on the sensor out of the 88
car there is a small round seal plug for adjusting the CO as on the 89
there is not if you are near any junk yards you might find a used one
place a Ohm Meter between pins 2&6 turn the screw very slowly the range
goes from 0-1000 0=full lean & 1000= full rich set to 700 Ohms
Glenn

--
"*-344-*Never Forgotten"
Is for the New York City Firemen who lost their lives on September 11,2001.
The official count is 343, but there was also a volunteer who lost his life
aiding in the initial rescue efforts. And I will never forget them as
long as I live,
nor should any American.