91 EJ22 poor mileage & cylinder #1 misfire only at fast idle

[91Beater]

[MISFIRE is solved. It was incorrectly installed throttle position sensor]

-----
Hello,
I'm new here. I already posted this on LegacyGT, but after seeing that this place is dedicated for first generation and the wealth of information I am seeing, I'd like to get some advise.

I got my 91 Legacy beater a few weeks ago and its getting bad mileage and misfires in cylinder #1 when I fast idle, but seemingly not when the car is moving. If I throw it in neutral, then fast idle, it won't misfire??

I'm getting 15mpg average.

It's got an NA EJ22. If I fast idle at 2000-2500rpm for a few seconds, RPM suddenly drops along with increased vibration. When I let off the gas at this point, it shudders and CEL comes on. It doesn't do it when I throw it in neutral and fast idle while the car is rolling fast; at least not yet.

I've been able to narrow it down to cylinder one by invoking a misfire by fast idling, then disconnecting injectors one by one.

During the misfire, removing anything but cyl 1 causes further vibration but removing cyl 1(psgr side front) doesn't make any difference, so I've determined that this is the misfiring cylinder.

When I listen by the tail pipe at normal idle, something sounds a miss and I can smell that smell you get after using outdoor power equipment in my hair.

If I have the auto tranny in gear, I can't get it to misfire/misfire enough to be noticeable.




So far:
new air filter
oil change (as if this makes any difference)
new spark plugs
Seafoamed through throttle body induction using Seafoam spray
Cleaned PCV valve, throttle body and MAF

I believe fuel filter is fine as there's no hesitation under heavy acceleration when fuel flow is the greatest.

I wanted to swap out injectors to see if problem follows it, but I couldn't figure out how to get them out

What do I check now?

The manual mentions flooring the pedal before starting the engine as a means of clearing flooding. I expected this as this is the norm with fuel injected cars. When I do it, it revs up through the roof as if the ECU doesn't know that the gas is pressed to the floor. I want to test the throttle position sensor, but I don't know the pin out or the values to expect.

[vrg3]

Welcome to the BBS!

The absolute first thing to do when the CEL is on is to read the trouble codes. Do that and let us know what you find. Start here: http://www.surrealmirage.com/subaru/engine.html

Then we'll go from there.

[jefferson]

+1 on checking the codes and I would replace your plug wires with some good ones, not the cheapies.

Jeff

[91Beater]

I'm going to check codes. I was thinking about swapping out injectors, but I have to think about that one. They've probably never been removed since the day the car was made. There was another thread about sourcing O-rings and apparently they're not so readily available. I read that it can be tricky to get them out, so I don't want to risk messing up the O-rings without having spares on hand first.

I've ruled out the plug wires. I swapped out cyl #1 and cyl #2 wires and misfire follows #1.

[Legacy777]

Welcome to the BBS.

As mentioned, pull the codes before you do anything else. I've learned that lesson the hard way. There's no point in guessing, when the computer will tell you what's wrong or at least give you a direction to start looking.

Based on what you've described, I'd suspect to see a code for injector #1. If that is the case, use a multimeter to check the resistance of each injector. They all should be roughly the same. If #1 is bad, its resistance will be way off.

[91Beater]

I'm making some progress here.

I didn't pull the injectors. Couldn't pull them out and I didn't want to risk damaging it.

One thing I forgot to mention in first post.

The "Power mode" seems sporadic. When I quickly floor the gas on the freeway, sometimes it goes into power, sometimes it doesn't. When I crank the car up with the gas pedal floored, it doesn't disable the injector as I expect with most fuel injected cars.

These made me immediately suspect the throttle position sensor and I think I'm heading the right directions. I believe the ECU uses the range of resistance and dR/dt (change in resistance over change in time) to make "power mode" determination. I believe the TPS is the only means of ECU's knowledge of how far the gas is pressed, which is why I guessed this.

The misfiring at fast idle stopped after I tweaked the mounting of TPS, but.. I'm not even sure if its even supposed to rotate in first place. I think its been removed at one point and didn't get put in properly.

I've identified the TPS to be reading about 0.55kohm at WOT, which is out of range. The resistance element also only read about 8.5 kohm, which is out of range from 10-12k ohm thats given on the information, but then I don't know how accurate that data is.

here's my hypothesis:
Vehicle stopped and given some gas: ECU thinks car is idle, because the idle switch indicates closed= idle despite the butterfly valve being opened, so this causes IACV to activate even though butterfly valve is open. I think fast idle behavior changes when the car is coasting in neutral, because VSS signal takes over.


The throttle position sensor has two oval holes and mine has enough freedom of motion that I could twist it around enough to not cause the idle switch to not close at idle. I'm not sure if there's supposed to be spacers to lock into exacting place.

I twisted too far "open" and it caused it to not activate idle switch which threw a code for defective idle switch.

What I did was twist it towards open so that it reads about 2kohm WOT. This is as high as I could get without causing the idle switch to not activate at idle.

After the adjustment, the noticeable misfire at fast idle stopped, and when I punch the gas on the freeway, it consistently goes into "power" mode.

The codes I pulled are
42 Abnormal voltage input entered from idle switch. Probably from when I twisted the sensor too far and caused it to never go into "idle"

24 Air control valve inoperative (Abnormal signal produced in monitor circuit). Not sure if this has anything to do with my diagnostic procedures that involved messing around with the TPS, running without TPS, etc.

31 Abnormal voltage input entered from throttle sensor. Obviously when I removed the TPS and started the car.

11 (no idea how) No signal entered from crank angle sensor, but signal (corresponding to at least one rotation of the crank) entered from cam angle sensor

14 Injector #1 inoperative. Probably because I pulled the harness to check for misfire.
14

[Legacy777]

What I would suggest first is adjust the TPS via these instructions:

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

The only means of adjusting the TPS is via the idle switch. If you adjust everything correctly and the TPS's main resistances are still out of whack, then yes I would agree you may want to look at replacing it. It's normal for the resistances to be off a little bit, but they shouldn't be way off.

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

Also, I would not recommend starting the car with the accelerator pedal floored. This will not disable the injectors.

Once you set the idle switch, clear all the codes, drive the car, and if the CEL comes back, check the codes again.

[91Beater]

Codes are away. I just noticed though, the car has a hesitation on a cold start in 0-15mph range.

[91Beater]

The brakes are not dragging. Obvious misfiring is gone.
I just got 16mpg on last fill up. UGH... I don't know what to do now

[Legacy777]

When's the last time you've replaced the coolant temp sensor?

[91Beater]

I just checked compression and I'm reading 140-160 psi across all four cylinders. I think that is reasonable, no?

I haven't been able to locate the sensor yet. I just know that there are two and one with two wires is the one used to report to ECU.

Is there a table of temperature vs resistance so I can check if its working properly?

In FSM, there is a way to read the sensor reading using a scan tool. Is there a way to do this without the proprietary scan-tool?

[vrg3]

If you can get your hands on a laptop with a parallel port you can try my free scantool.

[Legacy777]

The coolant temp sensor is located in the coolant crossover pipe. The two wire sensor is the one you want to replace.

Here's a picture. It's the brown plastic connector.

http://main.experiencetherave.com/subar ... P_2477.JPG
http://main.experiencetherave.com/subar ... P_2475.JPG
http://main.experiencetherave.com/subar ... P_2476.JPG

More various pictures
http://main.experiencetherave.com/subar ... injectors/

[91Beater]

Well, I'm not going to blindly replace it.

Is there a table of test points? i.e. 20C = xx ohm, 30C = xx ohm, 50 c = xx ohm....

[Legacy777]

You can find the resistance values in the troubleshooting section of the fsm.

http://www.main.experiencetherave.com/s ... ectrical)/

I will say that I've seen folks test the sensor and it test ok, but it actually be bad. It's roughly a $20 sensor from one of the online subaru dealers, which is why I usually recommend to replace it if it's never been replaced before or has a lot of miles on it. It's a critical sensor for the operation of the ECU's AFR. It may check out ok at a steady state temp test, but may be slow to react as engine temp changes.

[91Beater]

I've been getting 20 mix 27 long road trip the last few fills. I don't know what changed...