Hi everyone,

I recently purchased a 1991 Loyale 1.8L with SPFI.  When it starts, it will idle, but the RPM's slowly creep down.  "Feathering" the throttle will get it to rev, but it's unreliable.  The previous owner says this is likely the throttle position sensor.  Does that sound right or could it be something else?

Thanks in advance for any pointers!

Edited August 13, 20214 yr by Phil Hyde

Check the coolant temperature sensor also.  I have not had a problem with a TPS.  I took one apart recently,  they are incredibly well made.  Been running and maintaining EA82 powered wagons since 1988. 

32 minutes ago, DaveT said:

Check the coolant temperature sensor also.  I have not had a problem with a TPS.  I took one apart recently,  they are incredibly well made.  Been running and maintaining EA82 powered wagons since 1988. 

Thanks for the suggestion.  Would a bad coolant sensor cause major drivability issue?  I drove her to the back of my property.  You have to get on the throttle pretty heavy and keep pumping it for it to gain and keep RPM.  Seems to me like a fueling problem but that is also nebulous.

Have you checked for any codes ? 

Checked the fuel/air filters ?

Checked the fuel pressure ?

A bad CTS can cause major drivability problems.  And also, not nesisarily trigger a fault code.  Fuel pressure is critical also,  T a gauge into the line after the filter under the hood.  Iirc, it has to be 21 psi minimum.

3 hours ago, DaveT said:

A bad CTS can cause major drivability problems.  And also, not nesisarily trigger a fault code.  Fuel pressure is critical also,  T a gauge into the line after the filter under the hood.  Iirc, it has to be 21 psi minimum.

Thank you.  Is the CTS easy thing to check?  As in with a voltmeter?  According to the previous owner, the fuel pump and filter are new.  I know that doesn't mean the pressure is good, just a data point.

As for the other questions, sounds like I am going to need to check the trinity (fuel/air/spark) systematically.

I did a little searching and found reference to checking the CTS.  Seems like an easy check?

 

If this is the CTS (arrow), resistance at the connectors (red box) resistance seems in range from what I've read.  Ambient about 72F right now.

 

UPDATE: I unplugged the MAF sensor and the car started right up.  Maintains a ~2K idle and does not die.

So, bad MAF?

Also, I noticed this connector not attached to anything, and nothing obvious in reach.  Any ideas what it's for?

 

UPDATE: Cleaning the MAF had no effect.

6 hours ago, Phil Hyde said:

unplugged the MAF sensor and the car started right up

Indicates a faulty MAF

I check the CTS with an ohmmeter.  Run the engine till normal operating temp.  Shut off.  Log the temp immediately, and several time on the way back down.  If you don't have one of those IR thermometers, a meat thermometer works, just have to mechanically connect its sensor to the block.  Fill one of the unused holes with grease, stick it in kind of thing.

I have a few threads with temps vs ohms I made from values I collected of the years.
That other small sensor looks like the one on my CA car - it just verifies that the EGR is actually opening by measuring the heat in the passage.

2 hours ago, Dee2 said:

Indicates a faulty MAF

Thanks - it does seem like the obvious conclusion, doesn't it?

2 hours ago, DaveT said:

I have a few threads with temps vs ohms I made from values I collected of the years.
 

Dunno if this is yours but I found it here.

Edited August 14, 20214 yr by Phil Hyde

Here is my compilation of CTS data -

Subaru CTS temps.rtf

Can a MAF be tested by a shop?  I don't object to buying a replacement, but I don't want to plunk the money down only to find it wasn't the problem.  I've seen some testing procedures on YouTube but since my car won't idle it's a moot point.

Edited August 14, 20214 yr by Phil Hyde

Unplugging the maf just puts the ecu in the limp table. Dosent only mean a bad MAF. CTS/could be bad, ground could be, wiring could be bad. 

59 minutes ago, Ionstorm66 said:

Unplugging the maf just puts the ecu in the limp table. Dosent only mean a bad MAF. CTS/could be bad, ground could be, wiring could be bad. 

Here is the confusing part to me.  If the CTS is reading the correct value when cold, then how could a faulty part be causing the issue?

One way the CTS can fail is to read incorrectly when hot.  If the engine temp is not reported correctly to the ECU, it will not trigger the injector to supply the correct amount of fuel.   The result is running poorly.   A cold engine needs a lot more fuel to run well.  A hot engine will not run well with that higher amount of fuel.   I had a CTS fail so it randomly varied making all sorts of drivability problems.  But it never went out if range to trip a code.

A friend helped me source the factory service manual which has been a great source of information.  

Getting back to my original question for a minute - I performed the tests below and mine fails step 1.  meaning, it is not sending a closed signal to the computer.  Visual inspection suggests that the TPS is at its maximum CCW rotation, so I cannot adjust it.

Thoughts?

 

3 hours ago, Phil Hyde said:

A friend helped me source the factory service manual which has been a great source of information.  

Getting back to my original question for a minute - I performed the tests below and mine fails step 1.  meaning, it is not sending a closed signal to the computer.  Visual inspection suggests that the TPS is at its maximum CCW rotation, so I cannot adjust it.

Thoughts?

 

If you remove the TPS and rotate it gently by hand, will it read correctly? You can pop off the cover to the TPS and check the contacts, but be careful they are fragile from old age.

Edited August 17, 20214 yr by Ionstorm66

4 minutes ago, Ionstorm66 said:

If you remove the TPS and rotate it gently by hand, will it read correctly? You can pop off the cover to the TPS and check the contacts, but be careful they are fragile from old age.

I can't figure out how to completely remove the TPS.  I made another post in this forum about it.

UPDATE:  After removing the TPS, I was able to confirm that it reads "closed" (A-B continuity) in the throttle closed position.  A-B stop contacting at some small angle of rotation, which I assume needs to be adjusted to correspond to the feeler gauge specifications.

I re-installed the sensor and rotated so that A-B have continuity when the throttle is in the closed position.

Starting the engine produces the same result as before.  Idles up somewhere around 2K then dies.  Feathering the throttle will keep it running.

At this point I feel pretty confident that the engine should at least idle.  CTS reading checks out for cold start.  TPS is reading closed which should be good for idle.

Am I missing something?