I am trying to fix an insanely irritating idle problem on my 87 XT. EA82T engine MPFI. Its the one that sat for 17 after my dad fixed the heads and I recently got running. When it idles it wanders by about 200 RPM either way. The main big issue is that when it is in gear (Auto Tranny) it dies if you don't feather the throttle, as you can imagine that would make in town driving a pain. I have checked all the vacuum lines to the best of my knowledge. Scoured the shop manuals i have for the 86 year. Cleaned the idle air screw and the EGR air bypass solenoid as I originally thought it was the IAC valve. I have tested and replaced the vac line to the tranny from the intake manifold. And replaced the vac hoses from the pressure ports on the front of the throttle body. I cleaned the main throttle butterfly as it was suggested that that being dirty could cause this issue. I have triple checked the timing both valve and ignition. The only other thing i can think of it might be is the Aux Air Valve on top of the thermostat housing. I had pulled the electrical plug from it when it was idleing cold and it made no difference. It was my under standing that if you do that when its idling cold there is supposed to be a major idle change? I sort of suspect that it has to be a vac leak somewhere, because the engine gets kinda hot despite an upgraded cooling system and new thermostat. I have been beating my head against the wall about this problem for almost a month. If any of you can help me I would be forever grateful.

Dose it still die when its warmed up? If not it wont be the aux air valve, as it only raises idle when its cold.

 

If it's getting hot, I would thing turbo. Is there any oil in the intake post turbo?

@Ionstorm66 As far as I can tell, there is no oil in the intake. It does die when warmed up, stays fairly steady in RPMs but struggles and dies the moment you put it in gear.

Just throwing this out there.  Could be an airflow meter problem.  After all these years that "flexible" air intake hose isn't.  Check for cracks and insure ALL the smaller hoses are still attached. 

 

Many years ago my 85 XT turbo would just quit running.  Eventually discovered a ground wire attached to the intake manifold, right side , was corroded.  Whenever the ground was lost, the injectors stopped firing. 

Can you clarify a little....

Warmed to operating temp in Park.

You put foot on brake pedal to select Drive or Reverse with no foot on accelerator, and she dies?

Or is your accelerator feathering after Drive or Reverse selected and you go to drive off and she dies?

Warm to operating temp in park. Put foot on brake, no change just wanders the 200rpm like in park. I shift to drive or reverse, engine immediately begins to struggle then dies without throttle added. If I add throttle it runs as it should. If it needs to idle while in gear, like at a stop light the engine struggles then dies.

Edited September 26, 20205 yr by SiriusBlack

Maybe a fuel pressure problem (?)

PCV  valve if dodgy is another throttle body air bypass

How did I forget this one?

Try a block off cap on its hose tail

2 hours ago, Dee2 said:

Maybe a fuel pressure problem (?)

Supposed to be a new pump and concerns were new pump does not have a damper like original

It now has a new fuel pump and new damper. I also removed and thoroughly cleaned the injectors.

@Step-a-toe in order to be sure I have the right part this time, where is the PCV valve?

Edited September 25, 20205 yr by SiriusBlack

Positive crankcase valve ?

Everyone needs to know where this $5 service replacement consumable is ....at the back side of inlet manifold below throttle body. It takes in all the fumes from the 5/8 ID hoses off the rocker covers and all MPFi EA82 blocks have extra take off turbo side, back of block near knock sensor.

Is really just a poppet valve that normally will open on deceleration I think, sucking crank case fumey air. Can carbon up and leak air that can cause sh177y idle

Also, while you are chasing problems maybe make a block off plate for EGR valve as these usually block up with soot and can cause intake throttle bypass air. I had one cause weird issues

Since you are still probing for clues, I would do a fuel pressure check.  The tank may have sludged up the feed line to the pump.

Also, when the engine is idling, I would stick a vacuum gage on it and see if you can learn anything.

 

 

I am still running tests. I finished cleaning the egr valve, but haven't run it yet. I still need to block the PCV valve and test. The plug that runs to my coolant temperature activated sensor behind the intake manifold has its wires frayed right next to the plug. Does anyone know if I can acquire a new plug for that anywhere? Also will it hurt anything to just delete the egr solenoid valve that's under the intake plenum?

Two pin plug?

You might need to find a good donor plug and wires to splice to existing wires if you can't source replacement from an EFI specialist who may stock a remedy for you.

If you delete the solenoid you may throw an ecu fault code.

Some wire a resistor between the two pins so as not to.

If you can make a blocking plate as a gasket to install between EGR and manifold, seal it also, eliminates EGR completely from your diagnosis steps

My coolant temp sensor appears to be fine. It was the knock sensor that has frayed wires. I replaced the PCV valve and cleaned the egr valve. Double checked my vacuum lines again. Still no luck. I'm going to put a fuel pressure gauge on next and check that. In the meantime any other suggestions would be great.

Make sure the Idle switch is working on the TPS.

I'll be sure to check that too. Also, it was suggested that I see if I can get the car to tell me what's wrong with the diagnostic codes. It doesn't have the ECS light on the dash lit up, but how do I get the ECU to spit out codes?

Edited September 27, 20205 yr by SiriusBlack

42 minutes ago, SiriusBlack said:

I'll be sure to check that too. Also, it was suggested that I see if I can get the car to tell me what's wrong with the diagnostic codes. It doesn't have the ECS light on the dash lit up, but how do I get the ECU to spit out codes?

here's a link for reading codes.  I'm not sure where the test connectors are located on your vehicle.

https://www.troublecodes.net/subaru/

searching this website for ECU codes/connectors may bring up more specific info 

 

 

And while you are looking at TPS take note if the wiring just 30? mm from TPS has a three wire, possibly round, take off plug at all, something plugged in or not

AND how many wires to TPS itself

I have had three combinations I think.

Also think yours may be the 86 wiring, ECU etc flapper AFM likely it is TPSwitch not TPSensor as listed in diagram above

The LED for the codes is on the ECU.  On "regular" [non XT] the ECU is bolted to the steering column.  You have to remove the plastic cover to see it.

Just thinking of Rampages suggestion...

this thing stalls being shifted into D or R I think, this normally without any foot on accelerator, so throttle position do dad be doing bought but sit at idle

 

The previous image is from the 88XT manual. One connector.

The following image is from the EA82 manual. Two connectors one round and one flat.

 

6 hours ago, DaveT said:

The LED for the codes is on the ECU.  On "regular" [non XT] the ECU is bolted to the steering column.  You have to remove the plastic cover to see it.

On the XT the ECU is mounted in the trunk, just forward of the trunk lid. 

I will definitely check my TPS, as I recall mine has a rectangle connector, that probably goes into the wiring harness with the 2 large round connectors.

Oh, wow!  Never would have guessed that.