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1993 Legacy L -- Rough RPM Fluctuations & Rich Fuel Smell during warm-up


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12 replies to this topic

#1 union76

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Posted 25 June 2010 - 09:40 AM

I have a 1993 Subaru Legacy L auto (non-turbo) that starts up with a very rough idle (RPMs fluctuate) and rich fuel smell. Putting the car in drive doesn't help; it will want to lunge forward.

After about 3 minutes, the problem completely goes away and the idle is completely smooth. No check engine light. When the engine is warmed up, the warm-up idle is also smooth.The car starts and idles fine while the engine is still warm.

Could it be the MAF?
Spark plugs and wires?
IAC valve?

Thanks.

#2 Olnick

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Posted 25 June 2010 - 12:02 PM

How many miles on the car? Have you checked for any stored codes? How long since it's had a general tune-up? Plugs/wires, filters, PCV valve? Cleaning the MAF and IACV might help. Possibly the O2 sensor, ECTS (engine coolant temp sensor).

Just some random thoughts. Good luck.

#3 union76

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Posted 25 June 2010 - 09:27 PM

It has 260,000 miles. The last time the CEL came on was about a year ago, but for only about 2o seconds. I took it to Autozone, but they say that the light has to be on for their cheapo sensor to work. I don't know anybody in the area that has a true Subaru OBD-I scanner.

Plugs were installed at ~190k. New O2 sensor at 200K. Has new battery and alternator, and fresh oil change.

The air filter probably needs to be replaced. I will try some CCR cleaner on the MAF.

Thanks for the suggestion about the coolant temp sensor.
A 92 legacy on the board had a similar problem:
http://www.ultimates...ead.php?t=31428

I'll also point out that the transition from rough RPMs to completely smooth occurs very distinctly: generally at the 3-minute mark after ignition. It doesn't happen every single time at cold start up either. Since the problem started two weeks ago, I would say 30% of morning start ups are bad, and about 90% of afternoon start ups are bad, where ambient temp=100degs & very high rel. humidity.


This leads me to belief that it's not the spark plugs.

Edited by union76, 25 June 2010 - 09:36 PM.


#4 Olnick

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Posted 26 June 2010 - 02:36 AM

You don't need a reader to pull codes on pre-95 models, there are diagnostic plugs under the dash that allow you to check codes via CEL blinks. Here's an excellent how-to from Josh (Legacy777):

http://www.surrealmi...aru/engine.html

With 70k miles on your plugs I'd change them and the wires too--NGK coppers and Subaru OEM wires.

Definitely change the air filter. Also the fuel filter and PCV valve--clean the hoses leading to the PCV too.

Don't know if a new Engine Coolant Temperature Sensor (ECTS) wll solve your problem but after 260k it might be a bit "tired." New one sure helped my '95 Legacy a few years ago!

I'd suggest that you flush out the IACV--take it out of the car to do a thorough job. While it's out you will have a clear shot at changing the ECTS--believe me, it helps! Here's a link that may help a bit:

http://www.ultimates...ight=clean IACV

Good luck and keep us posted on how it's going.

#5 Olnick

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Posted 26 June 2010 - 02:53 AM

Here's another link to cleaning the IACV:

http://www.ultimates...dle air control

Good luck!

#6 union76

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Posted 03 July 2010 - 02:16 PM

Thanks so much for sharing the info on how to self-diagnose the OBD-I check engine light codes.

On my 1993 Legacy, there is no current code (using the black connectors). The last trouble code stored in memory is 21 (using the green connectors): "Coolant temperature sensor or circuit"

This site describes the location and how to replace this sensor on a 1995 Legacy:
http://www.lovehorse...TempSensor.html

Does anyone know if the procedure is any different for the 1990-1994 Legacies?

#7 Olnick

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Posted 03 July 2010 - 03:13 PM

Code 21 . . .Tah-dah!!!

The "lovehorsepower" writeup is excellent and I'm pretty sure it's exactly the same for pre-95 Legacies. Look under the IACV valve (passenger side rear of the engine) and if you see that brick red connector hidden below a jumble of harness cables and small hoses you're golden!

And you are certainly welcome for the help. Good luck, do post back and let us know how it goes.

#8 union76

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Posted 04 July 2010 - 03:53 PM

Just to be clear, is Code 21 for the ECTS (Engine Coolant Temp Sensor) or the CTS (Coolant Temp Sensor)? The CTS controls the temp gauge.

According to an image posted in a related thread, the ECTS is the brownished colored sensor on the 1994 legacy:
http://www.ultimates...p sensor&page=2

I am confused which item I should replace: ECTS or CTS? The brownish colored sensor will need a 19mmdeep socket on a 3/8 ratchet.

The price the dealer quoted for the OEM CTS is $59.66. Does this seem reasonable? Should I just go with the autozone equivalent?

Also noticed the CTS appears to be common problem for the Legacies:
http://autos.msn.com...el=Legacy Wagon

I noticed that the CV boot on the passenger side is completely cracked. I had a use axle put about 3 years ago. Any advice? Thanks.

#9 Olnick

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Posted 04 July 2010 - 04:53 PM

Yes, Code 21 is for the ECTS, the brownish colored one, it communicates with the ECU to make the engine run properly. The other one (blue?) is for the Temp Gauge on the dash (and frankly the ECU doesn't care what the gauge does!)

$59.66 sounds steep to me. Check online parts stores or call Jason, 866-528-5282. Autozone might be okay but I like to stick with OEM for such a crucial part.

Is the CV making bad noises? If not you're probably okay for awhile but it'd be wise to replace the entire half-axle eventually.

#10 OB99W

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Posted 05 July 2010 - 10:47 AM

The ECTS is indeed the sensor in question. It has a two-pin electrical connector (the single-pin one is for the gauge). They do fail, but it's also not uncommon for some corrosion to develop on connector pins. Before you replace the ECTS, you might try cleaning those contacts. Also, sometimes there's a poor contact in the multi-pin connectors at the rear passenger side of the engine.

#11 Fairtax4me

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Posted 05 July 2010 - 04:49 PM

I noticed that the CV boot on the passenger side is completely cracked. I had a use axle put about 3 years ago. Any advice? Thanks.


If it's not making noise yet you might be able to repack it and reboot it cheaper than replacing it.

#12 union76

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Posted 17 July 2010 - 03:38 PM

I completed the replacement of the brown ECTS unit. Having a mid-length 19mm socket was helpful. I didn't need to remove the PVC hose, but access to the sensor is still very tight. I lost about a liter of antifreeze when I got the old unit out. So make sure you have a reserve bottle on hand. The new unit came with a washer, and it was easy to thread in. The old unit appeared to be cracked at the plastic housing, although I might have caused that while torquing the socket.

I reset the ECU (plugged in both the green and black connectors under the dash), waited for the all clear signal, and disconnected. It's now been running fine for the last week.

Thanks for all your help.

Edited by union76, 17 July 2010 - 04:00 PM.


#13 Olnick

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Posted 17 July 2010 - 04:08 PM

Congratulations! Let's hope it continues to run fine for years, I know mine sure has!




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