Flormat

1986.5 auto U.S.
Car idles very low, 500 rpm or less but ok when around 3000rpm.
From the LH connector:
Terminals 3 & ground, closed throttle = 1 ohm
open throttle = 1252 ohm
2/3 open = 1202 ohm
Terminals 12 & ground, closed throttle = 1207 ohm
2/3 open = 1207 ohm

EZF plug readings
terminals 4 and ground, closed throttle = 1.1 ohm
open = 1374
terminals 17 & ground, closed throttle = 1294 ohm
2/3 open = .9 ohm

These readings don't match what the WSM indicates. Any thoughts?

JET951

Did you have both ECU multi plugs off at the same time during Ohms measurements ?

Mrmerlin

for TPS testing you want to find out if the idle circuit and the WOT circuit are working this simply means,
that open circuit happens,
IOW when the throttle is closed you want to see the connection go to no continuity,
when your opening the throttle you want to see no continuity when the pedal reaches about 3/4 or more for WOT.
From your posting you may be reading the wrong pins.

Flormat

No, was I supposed to? I checked one plug while the other was connected.

Mrmerlin

copy from a post of Bill Ball

You test on the EZF and LH harness plugs. The LH and EZF on 85 both have 25 pin plugs.

Pull off both EZF and LH control unit plugs.

To test the idle postion, connect ohmmeter on terminal 4 of disconnected EZF-control unit plug and ground.

Throttle closed = 0 ohm (max. 10 Ohm )
Throttle opened = inf. ohm
Idle contact must open immediately (< 1 degree throttle gap).

To test the WOT position, connect ohmmeter on terminal 17 of disconnected EZF-control unit plug and ground

Throttle closed = inf. ohms
Throttle switch after about 2/3rds of throttle travel = 0 ohms (max. 10 ohms )

Now, test the signal going to the LH plug

To test the idle postion, connect ohmmeter on terminal 3 of disconnected LH-control unit plug and ground.

Throttle closed = 0 ohm (max. 10 Ohm )
Throttle opened = inf. ohm
Idle contact must open immediately (< 1 degree throttle gap).

To test the WOT position, connect ohmmeter on terminal 12 of disconnected LH-control unit plug and ground

Throttle closed = inf. ohms
Throttle switch after about 2/3rds of throttle travel = 0 ohms (max. 10 ohms )

Mrmerlin

once this test is done I would consider sending the MAF for rebuild,
and replacement of the O2 sensor with a factory part not a universal O2.
Also inspect the IAC valve as they can get stuck so a new part should be fitted

Flormat

Thanks for the input. I am confident that I checked the correct terminals as I triple checked everything when I did not the readings I thought I should. The MAF has been rebuilt and then re-checked when it didn't fix the running condition. IAC i have removed and cleaned and also check by bridging terminals b and c on the test port. I will look into the O2. Thanks for the help.

Mike Frye

With the car off if you move the throttle by hand can you hear it click?

Definitely have to test with plugs unplugged or you're metering into the circuit of the other board.

Also verify at the plug under the hood if you still get funky readings.

One more thing: I had a problem where my TPS was resetting fine cold, but it was adjusted so tightly that when the engine warmed up it was just enough so the switch wasn't resetting. That one took me a while to figure out. Verify cold and warm and even if you hear it click it might not be making complete connection.

Mrmerlin

the real test of the IAC valve is to remove it,
then take a small screw driver and try to turn the center flap,
if you note that the flap seems to stick in one position then its probably a good idea to replace it.

What happens to the part is the brushes run at a certain spot and over time the brushes wear holes or depressions into the commutator ,
then after a while the brushes can stick in these holes thus the flap wont move quickly enough or far enough to compensate for the computer inputs, these are wear items.
It can be fixed by taking the IAC apart though the locking pins will usually break most of your tools trying to pry them open.
Once its open the you would remove the armature from the part then using silver solder fill the holes in the commutator then file flat them polish then refit.
For the time it takes to do this its better to install a new part

Flormat

The IAC is working, when I refreshed the intake I cleaned it, applied 12 volts and verified the valve opens and closes. Yes, the TPS clicks when I move the throttle slightly. I will re-test with both plugs unplugged and take a look at the O2 sensor. Thanks for the help.

WallyP

Look at the front of the engine, on the chassis crossbar, and find the idle stabilizer connector. This is a 1 1/4" round connector, with three electrical contacts under a cover, two on top, one on the bottom. Make a jumper to temporarily connect the contact located at the one o'clock position to the one at the six o'clock position. This kills the idle control circuit.

Look down between the first and second inlet tubes just on the passenger side of center, and find the round flat-slotted screw. Turn this screw to adjust the idle speed to 680 ± 20 rpm. Remove the jumper. If the idle is now steadier, the idle speed may have just been outside the range that the idle speed control could adjust. If there is no difference with the control active or disabled, the idle speed control unit may be bad.

PorKen

You are seeing >1200 ohms because both the LH and EZF have large internal resistors which protect the circuitry, so you have to unplug both to do a resistance test.


The TPS is not variable, just two switches (idle microswitch, and WOT carbon track wiper).



Technically, the LH accepts a variable WOT input, but it is programmed to just look for less than ~30 ohms for a WOT condition.

PorKen

Along the lines of what Stan said, the IAC/ICV may work with a full 12+ volts applied, but it may not work in the worn areas when rapidly cycled by the LH.

If the ICV is original (100K miles), replace it.

Mrmerlin

What Ken said,
just be cause it moves doesnt mean its good,
thus the testing with a small screwdriver to check for sticking spots in the flaps travel of the IAC

NOTE Doing these tests will provide you with info that most others will not see


NOW here is a link that will get you set up to figure out the whole system on your car

https://rennlist.com/forums/928-foru...maf+adjustment