Phil Hyde Posted August 13, 2021 Share Posted August 13, 2021 (edited) 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, 2021 by Phil Hyde Link to comment Share on other sites More sharing options...
DaveT Posted August 13, 2021 Share Posted August 13, 2021 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. Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 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. Link to comment Share on other sites More sharing options...
Dee2 Posted August 13, 2021 Share Posted August 13, 2021 Have you checked for any codes ? Checked the fuel/air filters ? Checked the fuel pressure ? Link to comment Share on other sites More sharing options...
DaveT Posted August 13, 2021 Share Posted August 13, 2021 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. Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 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. Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 I did a little searching and found reference to checking the CTS. Seems like an easy check? Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 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. Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 UPDATE: I unplugged the MAF sensor and the car started right up. Maintains a ~2K idle and does not die. So, bad MAF? Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 Also, I noticed this connector not attached to anything, and nothing obvious in reach. Any ideas what it's for? Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 13, 2021 Author Share Posted August 13, 2021 UPDATE: Cleaning the MAF had no effect. Link to comment Share on other sites More sharing options...
Dee2 Posted August 14, 2021 Share Posted August 14, 2021 6 hours ago, Phil Hyde said: unplugged the MAF sensor and the car started right up Indicates a faulty MAF 2 Link to comment Share on other sites More sharing options...
DaveT Posted August 14, 2021 Share Posted August 14, 2021 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. 1 Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 14, 2021 Author Share Posted August 14, 2021 2 hours ago, Dee2 said: Indicates a faulty MAF Thanks - it does seem like the obvious conclusion, doesn't it? Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 14, 2021 Author Share Posted August 14, 2021 (edited) 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, 2021 by Phil Hyde Link to comment Share on other sites More sharing options...
DaveT Posted August 14, 2021 Share Posted August 14, 2021 Here is my compilation of CTS data - Subaru CTS temps.rtf 1 Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 14, 2021 Author Share Posted August 14, 2021 (edited) 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, 2021 by Phil Hyde Link to comment Share on other sites More sharing options...
Ionstorm66 Posted August 16, 2021 Share Posted August 16, 2021 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. Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 16, 2021 Author Share Posted August 16, 2021 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? Link to comment Share on other sites More sharing options...
DaveT Posted August 16, 2021 Share Posted August 16, 2021 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. 1 Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 16, 2021 Author Share Posted August 16, 2021 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? Link to comment Share on other sites More sharing options...
Ionstorm66 Posted August 17, 2021 Share Posted August 17, 2021 (edited) 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, 2021 by Ionstorm66 Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 17, 2021 Author Share Posted August 17, 2021 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. Link to comment Share on other sites More sharing options...
Phil Hyde Posted August 18, 2021 Author Share Posted August 18, 2021 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? Link to comment Share on other sites More sharing options...
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