TPS - no trouble code reported

[stuckagain]

I continue, with much help from USMB and its' members, to work on a friends 1990 Loyale 4WD. I replaced the timing belts a couple of weeks ago and have been dealing with other small problems since.

 

The idle is a tad rough after the car warms up, rhythmic but rough, so today I thought I'd start checking things. Since I tested and adjusted the "idle switch" when I timed the engine I decided to check the "Throttle Sensor" resistance as outlined in Sec 2-7, of 1989 EA2 Service Manual available from www.finleyweb.net/default.asp?id=142 (PDF part 2, page 25).

 

The TPS in the Loyale has 4 posts referred to as A,B,C,D. The sensor passed one check and failed 2. I did get continuity from A and B as described in the manual (idle switch) but B and D read open rather than giving me the 3.5 to 6.5 k ohm the manual suggests. A check of B and C seemed promissing, but the connection went open after resistance rose a bit rather than slowly rising from 400 ohm closed to the prescribed 2.4+ k ohm at full open throttle (connection went open at same position as idle switch). The manual says that post B is supposed to be ground, but I get no reading between B and the metal throttle body.

 

Aside from the rough idle the engine, when warm, seems to accelerate OK - am I doing something wrong??? The TPC seems to be a very $$$ item unless I can find a working unit at a junk yard.

 

As always thanks for any pointers.

[Cougar]

I would suspect the B contact is purposely isolated from the metal ground. Is there a way you can clean the contacts to see if that will help?

[stuckagain]

I would suspect the B contact is purposely isolated from the metal ground. Is there a way you can clean the contacts to see if that will help?

 

I don't think I'd touch it until I have a spare. Spent some time searching old posts and found nothing about rebuilding one of these. I have a schematic from the Service Manual it labels the posts as follows:

 

A - Idle switch)

B - (GND)

C - Throttle position signal

D - + 5V

 

I assume the ground is for the ECU, perhaps it's isolated.

[Cougar]

Seeing the descriptions of the pins helps. It sounds to me that there may not be a real problem with the TPS. The ohm reading between B and D doesn't seem real important to me. Another thing you could check, after reconnecting things, is the voltage change between B and C with ignition on but the engine not running, as you move the throttle. If that changes smoothly from closed to WOT then I would think all is well with the TPS.

[idosubaru]

are the ER27 and EA82 TPS sensors the same?

 

theTPS in the ER27 motor (based on the EA82) will not come close to testing to the specs in the FSM - it's garbage. have to set it by ear. if the EA82 TPS is the same you could have the same problem. i've posted a couple times and have yet to see anyone mention if the TPS is the same on these two motors.

[stuckagain]

Another thing you could check, after reconnecting things, is the voltage change between B and C with ignition on but the engine not running, as you move the throttle. If that changes smoothly from closed to WOT then I would think all is well with the TPS.

 

I'm flummoxed! TPS now reads correctly ??? The problem has got to be me, I guess. Did everything the same as yesterday: cold engine, Fluke 87-V M.M., same leads. I triple checked all my readings yesterday so go figure. FWIW I started with your suggestion to read working voltage between B&C with the ignition on / engine off - 5V and dropped as resistance increased [if your new to Subaru repair see HINT below]. Surprised, I read the resistance on the connector lugs and came up with:

 

B&D 4.93 k ohm

C&B 0.5 k ohm (closed) to 4 k ohm (open)

 

I guess I saved a wad of cash but I've still got an engine that is running just a tad rough when warm. Air flow and IAC are OK so I'm off to test PCV and then EGR solenoid and if they check OK move on to vacuum hoses.

 

Thanks for the suggestions Cougar!

 

HINT: having never worked on a Subaru before I was using a small piece of phone wire to read signals from plugged in connector until I realized that you can peel back the rubber cover on connectors like the TPS and Airflow and then access the conncetions from the back of the plug (this is described in section 2-7, page 12 of the Service Manual "Air Flow Meter.")

[Cougar]

Your welcome for the help.

 

The only thing I can think that may have happened during the first readings is the scale on the meter was locked to a low value instead of autoranging, or on a high scale. When the reading went too high, then it would look like an open with the 'OL' reading.

 

Nice choice of meters by the way.