Stumbling and random idle (no longer dial up friendly)

[Smithcraft]

Recently I've started to get a stumble while accelerating, and sometimes after pulling up to a stop, the idle is erratic.

For the first part, I've found that with mild throttle the engine starts stumbling, almost like I'm lugging it, but I'm not. Applying more throttle seems to work past the stumble, and then at some point it seems like it's running on a different ECU and it's smooth as silk, or as silky as any boxer engine can be. This happens over different RPM ranges. I have also found that if I go from mild throttle to minimal throttle it smooths out and runs ok.

For the second part, when I come up to a stop and it drops to idle, sometimes it's fine and sometimes it drops way down then jumps up, and continues to oscillate till I either give it some gas or I get to go again.

I was thinking it could be the TPS, and I tried the tests from the Haynes manual. I did get nearly zero resistance with the throttle closed, but it went to infinite right away. Should it progress from zero to infinite or just jump, acting more as an on/off switch than a measured out put?
I also did the feeler gauge test and it was just about right with what the Haynes manual suggested.
I didn't have any pins to check the voltages through the connector leads though.

I tried a search but came up with 6400 hits, then I tried to restrict my search and came up with 3200 hits, so any suggestions other than search for it would be greatly appreciated.

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[Smithcraft]

Ok looking at Haynes illustration 4.3 I see that pins one and two are just a switch! I was just looking at 4.4, 4.5, and 4.6.

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[Legacy777]

Use this info for testing the TPS

http://www.main.experiencetherave.com/s ... sting1.jpg
http://www.main.experiencetherave.com/s ... sting2.jpg
http://www.main.experiencetherave.com/s ... sting3.jpg

[Smithcraft]

Thanks! It looks like the gap test(the third link) is good, but I'm gonna have to wait for a day when it's not pouring out to check the other tests.

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[Smithcraft]

Great goggly mogglies!

What are these things made of? Gold?

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[brweber352]

First off, I'm not sure exactly what a Legacy Mi is, if it is a turbo everything I write should pertain to this, if not, almost everything should still pertain to this.

I would start by looking for a metered air leak. A metered air leak will have a greater effect on light load and idle where overall airflow is the least. It will have the least effect where overall airflow is the highest, WOT.

Could be a sticky IAC, ever cleaned it?

How old is your O2 sensor? How old is your ECT?

I would start with the basics, clean your MAF, clean your IAC, look for metered air leaks, and maybe pull the plugs and take a look.

A good spot to look for air leaks is around the 90* turbo inlet boot, they tend to develop a large crack where the hose clamp is where it connects to the turbo, they also like to pull apart where the BOV connects. You can use black RTV silicone to patch the boot, just clean the area with brake clean first. Apply the silicone after everything is assembled with the hose clamp tight, let it set overnight before you drive. I just recently replaced my boot and it made a big difference, even though my silicone job was sealed quite well. The softness of the new boot is amazing, I thought they came hard as a brick from the factory .

Are you up to date on all your maintenance like plugs/wires. fuel filter, air filter?

Have you replaced all the sensors you should have by now like O2 sensor, ECT, updated knock sensor?

Are you running stock boost? If not have you upgraded your fuel pump yet? I went through 2 stock pumps before I realized the extra boost was killing them, I got a Walbro255 and been running great for 2plus years.(I doubt this is your problem)

I tried to convince myself since I got this car that the TPS was bad, I swaped throttle bodies several tmes and still tried to convince myself it was the TPS. After I did pretty much all the above the car runs better than I could have ever imagined, especially idle.

Hope some of this helps, Brian

[Smithcraft]

The Mi is not a turbo model(unless it's MikeyMeyagi's). It's a L with a skid plate, block heater, heated seats, and heated mirrors. It's also supposed to have some custom graphics.

Thanks for the advice though Brian. I do confess to being a bit behind in the service, but I kind of need to wait for a fair weekend to it tear into it.

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[Smithcraft]

Ok now that I have some alligator clips and a day that isn't pouring rain, and assuming I'm measuring the correct sensor, and I'm very sure that I am, this is what my TPS vs the FSM values.

• Pins 1 and 2 - same as FSM/Haynes.
  
  Pins 2 and 3 - 10.8k vs 3k to 12k
  
  Pins 2 and 4 - 10.3k vs 1k (throttle closed)
  
  Pins 2 and 4 - 2.2k vs 4.3k (throttle open)
  
  Pins 2 and 4 - Resistance change is smooth through the range of rotation, and no big jumps or gaps.

Anyone else wanna check their sensors to see if I'm doing something very wrong with measuring the TPS?

If I doing it right, then I'm kinda surprised that I'm getting readings that are the reverse of the FSM(unless there is an error in the FSM), and way out of range.

Also checked the air filter and it seems pretty clean with just a bit of dust/dirt in a circular pattern in middle of the element.

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[Legacy777]

Assuming you're measuing the correct pins, you resistance values are not what they should be. The FSM values are correct.

I would look at trying to swap it out for another.

[Smithcraft]

Thanks. I see a cheap JECS one on eBay. Anyone know if the JECS TPS is ok? I see many threads about the JECS MAF.

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[Legacy777]

There is only one type of TPS for the first gen legacy.

You have to be careful what you buy if you're looking at using a TPS from another car. These TPS sensors have a reversing resistance and also have an integrated idle switch.

[Smithcraft]

Yes, there is only one kind, but more than one company is making them for the aftermarket. I was thinking about getting a Standard Motors one, but they are as much as the Subaru part. I've never even heard of JECS but I see plenty of threads about their MAF.

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[RJ93SS]

genuine suabru parts have always worked better for me than any aftermarket product, especially sensors.

on another note

have you done the grounding mod, it helped to get rid of the hesitation i had between 3-4000 rpm and my car is completely rust free. it also helped the power windows.

and another thought, check your sparkplugs and be sure they are gapped correctly.

[Smithcraft]

I am planning on doing the ground mod. The plugs will most likely wait for a big job with the coil, and plug wires, that I hope to do in March.

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[Apex3]

Make sure you update when you get the new TPS in to let us know if it fixed it. My car does the exact same thing, I just assumed it was a vacuum leak that I couldn't find.

[Smithcraft]

Will do. The new TPS should be here tomorrow or Friday, since it's coming from Vancouver WA. And since they make you pay for priority it better be here!

And if it's good, then I'll post the link for their eBay shop. They have/had two more, and for a test part, the price just about can't be beat.

Otherwise, I hope it will fix the driving part, but I'm not sure it will have anything to do with the idle issue. However, with the resistance being as far out of wack as it is, it might...

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[Smithcraft]

Well, the replacement TPS was waiting for me when I got home from work.

I've checked the resistance, and it's much closer to what the FSM says it should be. Or something like that. I just hooked up the DMM and turned the knob as it were.

Depending on the weather I might get it in, in the morning, or it will have to wait for Saturday morning.

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[Smithcraft]

Replacement is in.

To anyone replacing a TPS I recommend having at least one extra of those dang tiny screws and washers. I spent a bit of time looking for the one that decided to visit the block right by the intake runners...

Hopefully it's mostly all good, and I'll find out today!

Resistance values are pretty good, but I'll check them again on Saturday when I have more time to putter about with it.

This is the ebay store I bought it from.

Looks like the JECS is the OEM part, as that was exactly what came off.

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[Smithcraft]

It's still not running right, but now I can accelerate again. I'm pretty sure something was definitely wrong with the old TPS as it rattles when shaking it.

The stumbling isn't as bad but it's still there.

The warm idle is still slightly rough, although I wasn't sure that part was related to the TPS.

I'm gonna let it sit over night, disconnected from the battery, and let it learn again in the morning.

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[Apex3]

Have you checked the coolant temp sensor? I'm gonna go check mine after reading this

When the CTS acts up [if you are lucky] you will get an engine light on the dash shortly after starting the engine. If you check the code with the ALDL you will get code "15." This should be your trigger to check the CTS immediately as the problem. When the sensor contacts go bad, the engine will perceive a coolant temperature of as low as -70 degrees. It will respond by opening up the Idle Air Control Valve (IAC) and running the engine mixture at full rich! You will notice the engine idle speed will be high from all the extra fuel. You should be able to smell all the extra exhaust fumes from the unburned fuel. Also you will find the engine to be less responsive to the throttle and perhaps even sluggish and quirky! All of these things happened to me the first time; when they happened again I knew what the problem was.

http://www.lotuselancentral.com/repair/cts.htm

Obviously this is about Lotus's but it should react similarly for other cars as well.

Might also check the idle control valve.

[brweber352]

OK, now that you've replaced the TPS, you might be able to stop thinking it is bad. You really need to focus on the maintenence items you know you've neglected, plugs, wires, maybe a good used coil, ECT, clean the IAC, clean the MAF, maybe a O2 sensor, updated knock sensor. You can do all this and then some for the price of a NEW TPS, it looks like you opted for a TESTED USED one so at least you saved $ here. You have looked for metered air leaks and vacuum leaks, right?

At times when your completely stumped, go back to THE BASICS.

Brian

[Smithcraft]

While I missed that post, I ended up picking up a set of plugs on Saturday, to start getting my ducks in a row for the big tune up in March.

Then I figured - Fnck it! I'll put them in now. Well it was late by the time I would have gotten started on Saturday, and starting to rain.

I did the plugs after running my Sunday errands. It had a set of Autolite Platinum AP 3923 plugs, and 7.5mm Autolite plug wires.

In order to make sure I didn't mess up the plug wiring order* I did one at a time, and brought the wires into the kitchen to wash them off and inspect them. Removing the old plugs was interesting to say the least. I don't think they used any anti-seize when they were put in. They all appear to have normal wear, but I think they may have been installed as the second or third set of plugs, as they were worn way, way, way down. When I put a new battery in my caliper, I'll see if can get a better measurement of the gaps.

I gapped the NGKs to about 0.039.

Here are the specs from the plug wires and the plug gaps.

• 1 - 5.56k ohms / 0.054 in
  2 - 5.04k ohms / 0.051 in
  3 - 5.82k ohms / 0.051 in
  4 - 5.90k ohms / 0.058 in

Boy was plug 4 a bitch! Maybe if I had smaller hands...

Plug for cylinder 3 was never installed all the way. The washers that should have seated against the head were an eighth of an inch from the nut part/base of the plug, and they were fixed there. I couldn't get them to move. I didn't want to mess them up, since I wanna get a pic of the plugs when the batteries for the camera get charged up. Eventually I'll try to remember to post them up.

So, it was test time. I checked to make sure that anything I might have disconnected by accident or on purpose was reconnected and fired it up to back it the rest of the way out of the garage(too much crap in the garage to drive it all the way in), and closed up the garage. The after warming up, the idle stayed pretty smooth ( ), but she puffed some smoke as I gave her some throttle to get down the driveway. I live on the edge of a bowl valley so I can do a fairly good load test either way I drive, so I took off and noticed quite a bit of smoke. More smoke than when I Seafoam'ed it... However she was running strong. Very strong! After a mile or two she wasn't smoking anymore. I tried every steep hill I could and she ran strong and pulled hard! I didn't notice any stumble.

The engine bay still smells like burnt oil though, which it didn't before. I'm thinking that most of the smoke and smell is coming from cylinder #3, where the plug wasn't in all the way and perhaps built up some carbon and crap that I pushed into the cylinder when I installed the new plug all the way down that I could.

So, I think I'll keep going as is, and see if the stumble and idle problems don't return in a week or three as the ECU gets used to the new plugs.

I also checked the two vacuum lines that I could see(the two in the vacuum sticker on the hood) and every other hose and tube in the engine bay that I could mess with and not really screw anything up with.

Just checked the plug wires in the dark to see if they were glowing and they looked nice and dark.

I think it's time to give her a name...

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* I'm sure it must be boiler plate in the Haynes manual about plug wire order that they put in every manual, but I can't imagine anyone being silly enough to mess up the plug wire order/routing on a DIS Subaru.

[Smithcraft]

Here we go with the pics (Sadly, I don't have macro adapter for the camera yet) -

Plug 1


Plug 3 (This is the one that wasn't installed all the way.)


Plug 2 (This head had a bad valve cover gasket which was serviced right before I bought the car.)


Plug 4


General view of the plug condition. All of the plugs are pretty similar.


Going through the old service records it looks like they were installed in July 2003, and did just over 104,000 miles in service.

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[douglas vincent]

Um, you are a moron?

Dude, its called a fucking tune up.

A tune up is done....

The moment you buy a car....

Plugs, wires, oil, filters etc.....

If you don't?

You get called a moron.

Nothing personal.

[Smithcraft]

Um, you are a moron?

Dude, its called a fucking tune up.

A tune up is done....

The moment you buy a car....

Plugs, wires, oil, filters etc.....

If you don't?

You get called a moron.

Nothing personal.

I may be a moron, but at least I'm not an asshole like you.

Way to go personal. Maybe you don't think so, but you did.

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