300E: test sticks on 10% duty cycle
I tried my new multimeter w/ duty cycle today (KAL 3002 by Actron, I got it on eBay before I saw the post about the Sears model)
I started with the key-on/engine-off tests. Koeo: 70% (actually 68.81%) this is with (-) trigger.
Depressed airflow sensor plate; 10% (actually 8.78%)
Open throttle completely, 20% (actually 18.97%)
When I released the throttle, the meter returned to 10% (8.78%). It stayed there until I started the car and bumped the throttle a few times.
I repeated this three times with the same results. The third time, I bumped the throttle without starting the car, and on the fourth or fifth bump, the meter returned to 70%.
Upon starting the car, the meter hovers around 50% for a couple of minutes and then steadily rises until it fluctuated between 79.75 and 83.75.
On one instance it got as high as 94%, but over several tries, it seemed to predominately stay between 79.75 and 83.75.
While fishing for the O2 sensor wires to disconnect them, I noticed idle RPM rising. I stopped, and went around front, and saw the meter at 8.78% steady. With RPM around 2000, I bumped the throttle for about 2 minutes until the meter came off 8.78% and returned to the 80's.
After this, I did disconnect the O2 sensor, and got 50% (48.91%)
Since 10% indicates airflow sensor position indicator (I am guessing this is the potentiometer) or idle speed contact switch, that is where I am headed tomorrow.
I expect it to be the pot, else the PO would have had it fixed.
Question is, are airflow meters normal wear items, such that I need to get a new one, or is this a random occurance, such that I can get one off a salvage car?
On the optimistic side, can anyone elaborate about the 'eraser on the potentiometer' process?
Or has anyone seen this before and know I am barking up the wrong tree?
This is on an 88 300E with 112,000 miles, but the car is from Long Island, and may have another 50,000 unrecorded miles from sitting stuck in traffic on the Long Island Expressway.