Bogging, Jerking, Hesitating at hot temperatures

[Btcox]

I have a 1995 Subaru Impreza HX Edition S (I'm aware that isn't a valid US model) visually similar to a sport wagon. This is a JDM Subaru so parts have not been easy to find for it due to me not knowing what US model it is considered. It is a right-hand drive vehicle, EJ18. The problem I'm running into is that when outside temp is hot/warm the car begins to bog or hesitate when accelerating. Never had this issue in the winter or fall. The warmer it got outside the worse the problem was. Idles fine and drives great in the morning when it's cooler but right at noon when the sun is blazing is when it starts acting up. This is my wife's vehicle, she is a postal driver so it's being driven for many hours each day. It seems that attempting to go uphill is when it acts up the worst once it's hot. I'm unsure what I need to do to fix this problem. Any help would be greatly appreciated.

Here is the list of parts I've already replaced:

New Oil Pan Gasket
New Rear Main Seal
New Oil Separator Plate and Seal
New Radiator
New Coolant Temp Sensor
New Coolant Gauge Sensor
New Spark Plugs
New Ignition Coil Wires
New Ignition Coil
New Fuel Pump
New Fuel Filter and Sock
New Air Filter
New Harmonic Balancer
New Serpentine Belts
New o2 Sensor and Bung
New Alternator
Added 2 transmission Coolers

[1 Lucky Texan]

'95 could have a separate Engine Temp Sensor - it may have 1 more wire thant coolant sensor and be located nearby.

also, you might consider vacuum gauge testing - compare cold with hot. some gasket or tubing may be failing at higher temps.

check system voltage too cold vs hot.

[heartless]

59 minutes ago, Btcox said:

New Spark Plugs
New Ignition Coil Wires
New Ignition Coil

what did you use for these items?

plugs should be NGK copper core
wires should be OEM or NGK ONLY - parts store wires are known to be problematic
coil - unless there was an obvious problem with the stock one, probably should have left it alone... aftermarket units are not the greatest here, either. used OE is better than aftermarket

Next question - is it throwing a check engine light at all?
if so, get the codes read and post here, in the order they show up.

if you dont have a code reader, most chain auto parts places will read them for free. they wont clear them, but they will read them for you

[Btcox]

52 minutes ago, heartless said:

what did you use for these items?

plugs should be NGK copper core
wires should be OEM or NGK ONLY - parts store wires are known to be problematic
coil - unless there was an obvious problem with the stock one, probably should have left it alone... aftermarket units are not the greatest here, either. used OE is better than aftermarket

Next question - is it throwing a check engine light at all?
if so, get the codes read and post here, in the order they show up.

if you dont have a code reader, most chain auto parts places will read them for free. they wont clear them, but they will read them for you

 

NGK Iridium IX Spark Plugs, OmniSpark Spark Plug Wire Set, Import Direct Ignition Coil.

I still have the original ignition coil so I can put that back on, plugs that I pulled out of if were mismatched, not gaped correctly and worn. After replacing all these parts, the problem didn't change so I left the new parts on.

No check engine light and no way to hook up to pull codes. Not sure how they do it in Japan, but I've looked everywhere for a port and have not been able to find anywhere an OBD reader could hook up to.

[heartless]

ok, 95 is still probably the single wire connectors under the dash... OBDII was not mandated until 96 here in the states.. not sure about elsewhere.. altho, my 95 Legacy had OBDII... so yeah.. kind of a weird year for that.

anyway, under the dash there should be two sets of test connectors, one set of green and a set of black.. both single wire - if they have never been used, they may still be taped up in the main harness bundle.. they should NOT be connected for normal operation.

you will need to do a bit of research cause I forget which set does what at this point (been a long time since i played with these)

[1 Lucky Texan]

yep, you might get a blink-code. check troublecodes.net - perhaps JDM uses the same definitions for the codes?

Edited May 15, 2022 by 1 Lucky Texan

[Btcox]

On 5/13/2022 at 5:28 AM, heartless said:

you will need to do a bit of research cause I forget which set does what at this point (been a long time since i played with these)

After research, Black to black plug pulls stored engine codes. I connected these and received a code 24

Reset ECU and waiting to see if the code comes back

 

22 hours ago, 1 Lucky Texan said:

yep, you might get a blink-code. check trublecodes.net - perhaps JDM uses the same definitions for the codes?

According to that website, code 24 is "Air control valve or circuit; Idle speed control solenoid valve"

Is this referring to the MAF sensor or the IAC solenoid valve, or both?

[laegion]

I'm going to assume it's referring the IAC, I don't think the maf is ever referred to as a valve. I would think they would say "air flow sensor" if they were referring to the maf.

[Btcox]

Gotcha, yeah that's a tricky one to find. Might have to just order a throttle body from UK with all the parts on it and see if that works.

Or see if a US throttle body will fit and install new US parts

[laegion]

9 hours ago, Btcox said:

Gotcha, yeah that's a tricky one to find. Might have to just order a throttle body from UK with all the parts on it and see if that works.

Or see if a US throttle body will fit and install new US parts

Yours doesn't have the separate iac motor? My '95 Legacy 2.2 has a separate iac unit bolted next to the throttlebody on the passenger side. I'm not familiar with pre obdii ej18 motors though.

[Btcox]

On 5/15/2022 at 1:22 AM, laegion said:

Yours doesn't have the separate iac motor? My '95 Legacy 2.2 has a separate iac unit bolted next to the throttlebody on the passenger side. I'm not familiar with pre obdii ej18 motors though.

I think your thinking of the device called a FICD or fast idle control device. That one adjusts the idle up when you turn the AC on

[laegion]

4 hours ago, Btcox said:

I think your thinking of the device called a FICD or fast idle control device. That one adjusts the idle up when you turn the AC on

In the FSM they call it an "Idle Air Control Valve", on parts.subaru.com they call it a "fuel injection idle air control valve". It looks like your engine is from the same generation as mine. but I see on parts.subaru.com that on the 1.8 that year it might be bolted into the throttle body on the drivers side.

 

Looks like Subaru doesn't make them anymore.

 

https://parts.subaru.com/a/Subaru_1995_Impreza-18L-AT-4WD-LE-Wagon/49232519__6030161/THROTTLE-CHAMBER/G10-063-05.html#22650

Of course this could be different for yours...but this is the closest to your model that I could get on this site.

Edited May 19, 2022 by laegion

[Btcox]

On 5/19/2022 at 3:06 AM, laegion said:

https://parts.subaru.com/a/Subaru_1995_Impreza-18L-AT-4WD-LE-Wagon/49232519__6030161/THROTTLE-CHAMBER/G10-063-05.html#22650

Of course this could be different for yours...but this is the closest to your model that I could get on this site.

Okay, l see what you are saying. I have that and a FICD which is mounted on the intake.

[Btcox]

Ordered a used throttle body assembly from the UK with TPS and IACV attached so I will try to use those when they get here but I tested both the TPS and IACV yesterday and both test good.

Removed the IACV and put 12 volts to it. It operates as it should with no binding that I can tell. Might be different under extreme heat but that would be harder to test.

TPS resistance moves smooth with no jumping. Again could be different under heat but hard to test.

Cleaned all the grounds under the hood. Car ran good in 70 degree weather for one day, then the following day ran awful at noon when sun was out and temp was in the 80's

Since I reset the ECU, I have not been able to get another code. I plugged the 2 black wires together, I think those are used for view stored codes and have not been cleared.

Is there anything else I should replace or anything else I can test/check for to find the issue? Someone at her work mentioned it could be the ECU overheating but I think those are located inside the car under the glovebox which should stay cool being inside the car, so I kinda doubt that but I could be wrong

 

[laegion]

1 hour ago, Btcox said:

Ordered a used throttle body assembly from the UK with TPS and IACV attached so I will try to use those when they get here but I tested both the TPS and IACV yesterday and both test good.

Removed the IACV and put 12 volts to it. It operates as it should with no binding that I can tell. Might be different under extreme heat but that would be harder to test.

TPS resistance moves smooth with no jumping. Again could be different under heat but hard to test.

Cleaned all the grounds under the hood. Car ran good in 70 degree weather for one day, then the following day ran awful at noon when sun was out and temp was in the 80's

Since I reset the ECU, I have not been able to get another code. I plugged the 2 black wires together, I think those are used for view stored codes and have not been cleared.

Is there anything else I should replace or anything else I can test/check for to find the issue? Someone at her work mentioned it could be the ECU overheating but I think those are located inside the car under the glovebox which should stay cool being inside the car, so I kinda doubt that but I could be wrong

 

Have you replaced your PCV valve recently? Does your motor have EGR?

[Btcox]

4 hours ago, laegion said:

Have you replaced your PCV valve recently? Does your motor have EGR?

Have not replaced PCV valve and no to the EGR

[laegion]

7 hours ago, Btcox said:

Have not replaced PCV valve and no to the EGR

I would definitely replace that if you don't know when it was last done; it's likely worn out. They can cause some definite running problems.

[Btcox]

On 5/20/2022 at 11:28 PM, laegion said:

I would definitely replace that if you don't know when it was last done; it's likely worn out. They can cause some definite running problems.

Alright I have replaced the PCV valve and am still having the same problem.

Additionally, I swapped out the IAC and TPS with another used one I purchased from Japan. Those test fine as well.

Should I start looking into an ECM or possibly the MAF sensor? I'm running out of ideas

Here is a video of it acting up. Not sure if this will help or not

 

[1 Lucky Texan]

another longshot - clean or replace the crank position sensor. Sometimes metallic debris collect on it (often from failing bearings - looking at you Toothed Idler).

[Btcox]

On 6/1/2022 at 10:23 AM, 1 Lucky Texan said:

another longshot - clean or replace the crank position sensor. Sometimes metallic debris collect on it (often from failing bearings - looking at you Toothed Idler).

Replaced the crankshaft position sensor, same issue.

The other day my wife ran it too low on gas and experienced the same issue. I'm thinking maybe I need to replace the fuel injectors next

[laegion]

1 hour ago, Btcox said:

Replaced the crankshaft position sensor, same issue.

The other day my wife ran it too low on gas and experienced the same issue. I'm thinking maybe I need to replace the fuel injectors next

If you need some rebuilt injectors I found a place that does cleaning and flow matching, provides all new seals, and provides a lifetime warranty on theirs. My car has been running well on some of their rebuilt injectors for several weeks now. 

I can't endorse them or anything since I've only done business with them once, but they seem really reputable and their ebay rating is really good. (which is where I found them) 99.3% with over 24k transactions.

https://www.cspinjectors.com/

[Btcox]

2 hours ago, laegion said:

If you need some rebuilt injectors I found a place that does cleaning and flow matching, provides all new seals, and provides a lifetime warranty on theirs. My car has been running well on some of their rebuilt injectors for several weeks now. 

I can't endorse them or anything since I've only done business with them once, but they seem really reputable and their ebay rating is really good. (which is where I found them) 99.3% with over 24k transactions.

https://www.cspinjectors.com/

Thanks! I will definitely look into that

[el_freddo]

Don’t replace your injectors. Your issue is either a dying fuel pump or the ignition module on the firewall is getting too hot. More likely your fuel pump is dying, although when mine died under high temp conditions (<30km/h driving in sand during the warmer months, fine at cruise and around town), the engine would stall out and be a PITA to restart immediately - at which point it would stall out again shortly after. 

The other thing you could check is power at the main relays. Hook up a multi metre to watch when the issue shows up. If the voltage is jumping with the engine revs there’s an issue with the relays. Same for the ecu power. 

The reason why I’m suggesting the power issue is because of the way the rev counter jolts you and down - as if power is suddenly cut then reinstated in a repetitive cycle. 

I’m guessing this issue just keeps going on and on? At what point does the car “snap out” of this behaviour? 

Cheers 

Bennie

Edit: as for parts, the engine and gearbox are phase 1 gear. Basically the same as the EJ22 legacy. The engine sensors etc are interchangeable. Someone will correct me on the specifics of what’s different but essentially they’re all the same. 

You might be able to find a FSM from Japan or Australia as we got the impreza from the first model in 1993 or 1994 (I’m not sure which year the impreza started).

Edited June 7, 2022 by el_freddo

[Btcox]

14 hours ago, el_freddo said:

Don’t replace your injectors. Your issue is either a dying fuel pump or the ignition module on the firewall is getting too hot. More likely your fuel pump is dying, although when mine died under high temp conditions (<30km/h driving in sand during the warmer months, fine at cruise and around town), the engine would stall out and be a PITA to restart immediately - at which point it would stall out again shortly after. 

The other thing you could check is power at the main relays. Hook up a multi metre to watch when the issue shows up. If the voltage is jumping with the engine revs there’s an issue with the relays. Same for the ecu power. 

The reason why I’m suggesting the power issue is because of the way the rev counter jolts you and down - as if power is suddenly cut then reinstated in a repetitive cycle. 

I’m guessing this issue just keeps going on and on? At what point does the car “snap out” of this behaviour? 

Cheers 

Bennie

Edit: as for parts, the engine and gearbox are phase 1 gear. Basically the same as the EJ22 legacy. The engine sensors etc are interchangeable. Someone will correct me on the specifics of what’s different but essentially they’re all the same. 

You might be able to find a FSM from Japan or Australia as we got the impreza from the first model in 1993 or 1994 (I’m not sure which year the impreza started).

Thanks for the info!

After the issue starts it does not stop until the car has cooled down. The typical quick fix is to pull over, turn off engine, and wait for it to cool down, then start up again and drive for a few minutes until it does it again. The problem does not occur at engine operating temp but is weather/heat related somehow, typically when it's over 80 degrees Fahrenheit on a hot sunny day. The hotter outside, the worse it gets, typically under a heavy load (accelerating or going up hill). No check engine light has ever come on.

So, the fuel pump has been replaced already but I have not replaced the ignition module. I'm attaching a picture to make sure I'm thinking of the correct part you are talking about

[azdave]

Do you have a can of Dust Off?  The contents are R152a which is a great refrigerant. If you think it might be the ignition module (which could fail in the heat as you describe) then invert the can and spray several short spurts to cool off the part and then see if you can drive much further before the failure returns. Even cooling it with a handful of ice might prove or disprove this theory.

My 87 Mazda B2000 had an ignition module fail in this same manner and an Icee slush drink from the convenience store got me home. Cherry flavor works best.