94 940 Rough idle after air filter change? AMM?

I just replaced my air filter in my 94 940 with a K&N. In the process I
disconnected the air mass meter harness so I could move the top half of
the air box out of the way. Immediatey after I installed the new air
filter (and replugged-in the AMM harness) the idle became a little bit
rougher and in the next couple of days countinued to worsen. At this
point the car occasionally dies at idle. The idle is rough, but in a
pulsing or surging kind of way thats very consistent. I feel like the
problem is in the AMM area because after starting the car, I've
unplugged the AMM harness and plugged it back in, and the idle
smoothens out for a while. Anyone have any input as to what might have
happenned here? I'm going to clean the harness and amm connection and
gob on some fresh dielectric grease and see if that helps.

 

I'm sure you're on the right track. The AMM connector is a common enough
problem, and sometimes reseating it (like you did) can stir up evil spirits.

I've had fair luck cleaning mine with isopropyl alcohol. I dunno about
dielectric grease. Hi-fi shops also carry a contact improver called "Tweek"
(sp?) that is a block polymer (whatever that is) in an isopropyl carrier.
Supposedly it is conductive in thin films and insulating in thick films.

Mike

 

Thanks, I cleaned the harness terminals with some iso alcohol and a
small brush. Upon first starting the motor, the idle seemed to be
better. Then all of a sudden the idle began surging/pulsing again and
soon went away. I've taken a couple drives around the block and the
same thing happens regularly. Idle will be nice and steady and then
sporadically will start surging and then go back to being nice and
steady. I dont get it. Anyone?

 

Another thing: When in Drive with my foot on the brake the idle is
fine, but once I put it in park the idle begins pulsing and almost dies
repeatedly. Why? With the engine on I pulled the AMM harness to see if
the idle improved, and it severely worsens, but once I re-plug the
harness, the idle evens out and the idle surges stop. I'm guessing I
need a new AMM.

 

Roland, this is just a thought, but with the engine running and the AMM
in place, remove the K&N filter and see how the engine runs. I wouldn't
run for long like this, and if you have another filter to test, that
would be best.

Perhaps the K&N is choking the engine. Be sure to check and make sure
no vacuum hoses were loosened or removed when you removed the AMM and
assembly on that end.

 

another thought is that you might have introduced an air leak when you were
working on changing the air filter. Perhaps one of the ducts has a split or
weak spot that opens to introduce additional air, which upsets the air/fuel
mix... Or you might have dislodged an air line leading to the intake
manifold, causing the same thing... go back over your connections before you
replace the AMM....

A few years ago, I used a small straightpin to GENTLY push the little metal
"fingers" in the AMM connector closer together, giving a better contact.
Solved the problem I was having, but be careful!... And I use a little spray
of PRO-GOLD, a contact enhancer, to improve the conductivity...

 

The problem is getting worse. On the freeway tonight while going about
60 the idle was periodically dropping a few hundred rpms or more and
finally while on an exit ramp the motor died and wouldnt start up right
away. I had to rev the motor quite a bit to get it going. Also the
engine is running very rich. I can smell it in the exhaust. I've
cleaned the AMM harness and inspected all of the vacuum hoses and all
the hoses that run into the intake manifold and they all seem ok.
Tomorrow I'm going to replace the spark plugs and fuel filter,
something I had planned to do before all of this as part of a tune-up,
and if the problem persist I'm going to drive my car into the river.

 

fuel pump, or fuel pump relay. While you are there, put in your new fuel
filter as well.

My '89 240 has the main pump under the car, behind the left rear wheel, and
an in-tank pump... supposedly, the car will run without the in-tank pump,
but when the gas level gets low, the main pump might have trouble pulling
fuel out. Also, there is a little rubber hose between the in-tank pump and
the delivery tube, and if that develops a tear, the main pump will suck air
when the fuel level drops below the tear....

suggest you fill the tank, and see if that solves the problem. If it does,
your intank pump or hose is bad. If it doesn't help, I'd go for the main
pump... They are relatively cheap at places like Autozone...

m9876c at yahoo dot com

 

forgot to mention... there's a large fuse mounted on the left firewall, near
the ignition coil... this is apparently the main fuse to the engine
electronics, and if it is loose you will have the engine cutting out... been
there, done that! Check that fuse (30 amp, I think) and make sure it's
seated firmly....

 

Check your fuel pump relay. It gives similar symptoms when going bad. I
replaced the one for my 940 for less than $50 (USD) and 30 minutes of time.
In my case, it solved the problem; it may or may not be the same issue you
are experiencing, and the timing of it with the air filter change could be
coincidental.

NCMan