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BillSalzer

95 Impreza L 1.8 Obd1 Stalling Out need a Subaru Guru!

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My 95 Impreza is been a pain from a cold start the car runs great for about 15-20 min An then starts to spit An sputter an eventuality bogs down An dies like it’s running out of fuel , I’ve replaced plugs,wires,coil, mass air, TPS, crank sensor, cam sensor , fuel filter , tested fuel pressure, An it’s not throwing any check engine lights however when I pull up the test wires it gives a code for mass air flow An tps .... any ideas? Need help!

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Clean and or change the Mass Air flow sensor.  Used Subaru one is fine.

Make sure the ducts and tubes off the airbox are in good condition and tight.

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What does “pull up the test wires mean”? I assume you’re checking memory mode?

 

If you’re getting a code for those items I’d focus on those items:

 

Clear them both and see which one comes back first. Focus on that one.

 

Ive located some troubling issues like this (including a TPS) by locally massaging the wires until the symptoms change (get worse or better). Start at the sensor and work your way back as far as you can. It was about 4 inches from the TPS. I Cut off the connector and spliced in a used one and good to go. But that only works if you can test while idling (engine will stall, run better or rev) or someone keeps trying to start it while you jockey the wiring around.

 

Ideally follow the FSM diagram for troubleshooting the code.

 

Check connector(s) for damage.

 

Check each wiring harness for those sensors for rodent damage. They’ll crawl up and nibble wiring. I’ve repaired a couple of these over the years.

 

Look at the FSM wiring and see if the TPS and MAF are related in any way.

 

Test each wire for the sensor(s). Check Continuity and resistance between the engine side connector and the large main connector at the back of the engine on the passengers side. FSM will show you which wires are the culprit.

 

Ideally you test from the sensor to the ECU but that’s more difficult just due to location. Engine connector is easy as it’s right next to those two sensor connectors.

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Yes Idosubaru when I said pull up the test wires I was reading the codes An it sets tps An mass air at the same time every time, An I have been all over the harness An connectors with my multimeter An had someone inside the car trying to start it while I wiggles wires everything seems to be in spec... I also replaced the timing belt, Tensioner, idlers, An crank gear about 6 months ago before this ever started An I did pull it back apart to check timing last week.

 

Generaldisorder I ordered one just now it’ll be in when I get off work so I’ll try it tonight .

 

One thing I forgot to mention is that when it does this I can cut my key off An back on An it runs fine for about 3-5 seconds An starts acting up again, the last 2 times I drove it I had to keep turning the key off an on to make it home.

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The codes may be meaningless - I have a 90 Legacy for example that intermittently has about 5 sensor codes and has run perfect it's entire life. It has 316k on it and runs flawlessly and gets over 30 MPG. The OBD-1 stuff was prone to poor grounding issues and it wouldn't be the first dodgy computer I've seen either. I believe everything on the 5v rail on mine throws a code. It's never been a "real" issue and the previous owner just learned to ignore it. Now I own it and I may put more effort into locating the issue but it's not affecting how it runs or drives. The ECU's.... they get old and weird or sometimes fail. 

 

To really know what the issue is you need to look at live data, but that requires some software (EVOScan), and a special SSM-1 to USB cable and some computer knowledge to setup. Or the use of a Subaru Select Monitor with the appropriate cartridge. 

 

The CTS is at high resistance when cold, and as the engine warms the resistance drops. You can measure it if you are inclined to do so... there are two sensors - one for the ECU and one for the gauge. You want the ECU sensor with the reddish brown connector (2 pin). It's on the back of the coolant cross-over below the PCV valve area. If, as I suspect, the resistance doesn't drop when warm, then engine will flood out and die as the computer is still on cold idle (choke) mode. The ECU can't detect that this is incorrect - it doesn't have the algorithmic complexity to do so. If you are going to do the resistance check it's important to check it at the ECU pins as well. High resistance in the circuit would have the same effect as a bad sensor. 

 

GD

Edited by GeneralDisorder

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What do they do if the CTS plug is pulled? If they run with the plug pulled that would be a quick 30 second test. Pull the plug the next time it starts stalling?

 

Isn’t the O2 sensor ignored when the car is first started and driven and picked up once the car reaches operating temperature? Could the O2 sensor be bad?

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I'm not sure what that computer would do. A lot of the early ones didn't handle circuit faults gracefully. Could try it. But getting to the sensor is hard enough - might as well check the resistance at the ECU terms first. Assuming you have a DMM and some back probes or paper clips. 

 

GD

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What do they do if the CTS plug is pulled? If they run with the plug pulled that would be a quick 30 second test. Pull the plug the next time it starts stalling?

 

Isn’t the O2 sensor ignored when the car is first started and driven and picked up once the car reaches operating temperature? Could the O2 sensor be bad?

Won't make a difference. The OBD1 ECUs don't have way to determine an open circuit fault. A dead CTS is quite often an open circuit. The sensor element is electrically open and will read infinite resistance if measured with an ohmmeter.

 

It's a common failure and a new CTS is about $20.

 

O2 sensors fail in two ways, either high voltage, or no voltage. If the sensor sends you voltage the ECU assumes the fuel mixture is rich and will lean out the mixture if it can, but older systems can only alter the AF ratio by about 15% based on O2 sensor signal. In the right conditions the lean AF ratio can cause some stumbling or hesitation but I've never had one make an engine stall.

The O2 sensor sending no voltage the ECU will assume the sensor hasn't reached operating temp and will continue to run on base AF ratio which will make the engine run like nothing's wrong, just won't be as fuel efficient as it can be.

I'm not sure what the algorithm is for setting codes on the OBD1 ECUs, but usually just unplugging something doesn't do it.

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Would a Idle Air Control Valve cause this I don’t know how important they are on a Subaru, my car has idled about 300-400 rpms when warm all summer An now its idleing around 800-1000

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I replaced the temp sensor yesterday An no change...

 

Are you positive you replaced the correct one?  Subaru's can have multiple coolant temp sensors.  Such as one for the gauge, one for the cooling fans, and one for the ECU. 

 

You want to replace the one responsible for the ECU.

 

Would a Idle Air Control Valve cause this I don’t know how important they are on a Subaru, my car has idled about 300-400 rpms when warm all summer An now its idleing around 800-1000

 

300 rpm's is really low, unless it's just inaccurate when it's at the bottom of the range?

 

IAC's are one of the more problematic parts over time, they are electronic and have moving parts in them. Sometimes they can be cleaned if they are simply sticking due to build up. 

 

But I do not know if they'd cause your symptoms, that's not the classic symptoms and I haven't seen it, but that by no means rules it out.

 

Classic IAC issue is the car stalls when you press the brake, come to a stop, or take off from a stop.  But I'm sure that can vary.   I've never seen one cause the issues you're describing but I'm sure they have various failure modes and the ambiguity of describing symptoms on a keyboard isn't always ideal. 

 

Your vehicle easily swaps ECU's - just buy the cheapest one in the country for a few bucks and they're plug and play.  And late 80's stuff and 95 stuff  you don't even have to pay attention to automatic/manual, the ECU's are interchangeable between them, but I'm not familiar with 90-94 EJ's. 

www.car-part.com

 

ECU's fail so rarely that new is pointless and used is a great bet.  Someone on here may even have one for you. 

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By the way I want to thank everyone for all the help I’ve been on 4 different Subaru forums an no one has offered any help or info. This is by far the best one I’ve found!

Edited by BillSalzer

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Low idle could be due to a vacuum leak or split or broken hoses connecting to the intake tubing.

 

The IAC does have primary control of idle speed. It is common for those to get gummed up and cause some issues usually with idle surging up and down. It can be cleaned on the intake by spraying it with throttle body cleaner or seafoam spray cleaner.

You can also remove it to clean but that also requires a new gasket.

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