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Check engine light on, but smooth idle


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12 replies to this topic

#1 jeansain

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Posted 28 December 2004 - 09:54 PM

What is the most likely cause of a check engine light, when engine performance and idling is OK?

Happened just all of a sudden this morning when I went to start the car. The starter turned but the car the car didn't start at first. I then tried again and it fired after a brief hesitation but the check engine light stayed on.

Now it starts fine but the CEL is still on. Any ideas?

#2 lmdew

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Posted 28 December 2004 - 09:58 PM

Best thing to do is have the codes read. It could be many things. Here in the US, Autozone will read them out for Free. Check around, you might find a similiar deal near you. Let us know what you find.

The spouse filled up the 98 Outback Legacy the other day and later the CEL came on as the gas cap was not tight.

#3 jeansain

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Posted 28 December 2004 - 10:17 PM

Some info that may be useful:

Since the very cold weather started, once in a while, there is a strong gas smell inside the car. I am thinking it may be the charcoal canister (if there is one in this car). If that is the case, there may be a connection, since most CEL are emission related. Any thoughts?

#4 Gnuman

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Posted 29 December 2004 - 12:13 AM

Some info that may be useful:

Since the very cold weather started, once in a while, there is a strong gas smell inside the car. I am thinking it may be the charcoal canister (if there is one in this car). If that is the case, there may be a connection, since most CEL are emission related. Any thoughts?

That has been hapening to a lot of people, check all the clamps on all the gas lines (particularly the ones near the headers), and make sure the gas cap is on tight.

Oh, and it may also be that your avitar is distracting your car. . . .:brow:

#5 cookie

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Posted 29 December 2004 - 01:04 AM

but in some cars you can trigger a code with a hard cold start. If it dumps raw gas down the system the ox sensors can go nuts. I would see if it would not go away with a few cycles. I am not sure if this happens on Subies but it is a common problem on a BMW that gets parked in the cold for a few days. When the battery gets weak seems to contribute. On Bimmers it clears up with regular running after a few starts.

#6 wowie

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Posted 29 December 2004 - 01:17 AM

Hi! I just joined the USMB to look for this very problem. After driving for awhile the check engine light will come on and stay on for varying amounts of time, sometimes until I turn off the car. I have also had a decrease in fuel economy by about 3 or 4 mpg. The car runs fine otherwise. It is a 1990 Legacy AWD wagon with AT and 153k. This has been going on for several months, since before cold weather.
Several mechanics have told me this age car doesn't save codes easily. Unless the light is on they won't be able to get a code.
I suspect the emissions system somehow.
Sorry jeansain, didn't mean to hijack your thread.

#7 Gnuman

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Posted 29 December 2004 - 01:26 AM

Hi! I just joined the USMB to look for this very problem. After driving for awhile the check engine light will come on and stay on for varying amounts of time, sometimes until I turn off the car. I have also had a decrease in fuel economy by about 3 or 4 mpg. The car runs fine otherwise. It is a 1990 Legacy AWD wagon with AT. This has been going on for several months, since before cold weather.
Several mechanics have told me this age car doesn't save codes easily. Unless the light is on they won't be able to get a code.
I suspect the emissions system somehow.
Sorry jeansain, didn't mean to hijack your thread.


You didn't, really. . .
the 1990 Legacy is OBDI, and the codes are a series of flashes of the light when in check mode. There are detailed descriptions of how to read the codes on page 6-3 of the Haynes manual that covers your car (number 89100). If you need, I can scan it and post that page. Josh, do you have that info already scanned?

#8 wowie

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Posted 29 December 2004 - 02:05 AM

After reading your post I dug out a Chilton manual and found the section on codes. They didn't specifically list 1990, rather 91-94 on page 4-23. Guess I'll have to look for a scan tool or tester.
Can you think of anything that would make the gas mileage go down? Instead of 20-30 I'm getting 16-26 depending on the highway/city mix.

#9 Setright

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Posted 29 December 2004 - 02:41 AM

Sounds like it could be the "canister purge valve". Quite a common fault, that triggers the CEL but doesn't alter performance dramatically.

Valve is located around the intake manifold and has wires and small vacuum hoses attached. Easy to replace, but make sure you do the "battery dance" ECU memory wipe.

#10 wowie

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Posted 29 December 2004 - 03:09 AM

Sounds like it could be the "canister purge valve". Quite a common fault, that triggers the CEL but doesn't alter performance dramatically.

Valve is located around the intake manifold and has wires and small vacuum hoses attached. Easy to replace, but make sure you do the "battery dance" ECU memory wipe.

Thanks for that Setright. I'll take a look. By "battery dance" I assume you mean disconnecting it to clear the codes. According to my manual, you do something different on cars through 94. It says: "With the ignition ON and the engine running, connect both the read memory terminal and the test mode terminal."

#11 Gnuman

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Posted 29 December 2004 - 07:37 AM

Thanks for that Setright. I'll take a look. By "battery dance" I assume you mean disconnecting it to clear the codes. According to my manual, you do something different on cars through 94. It says: "With the ignition ON and the engine running, connect both the read memory terminal and the test mode terminal."

On your car, just to the right of the column (facing front) there is a large yellow connector with a pair of blue "T" shaped connectors with one wire coming out of each. These will probably be connected together. To check the codes, disconnect them and turn the ignition on (without starting the engine) and watch the Check Engine Light (CEL). The trouble codes are two digits long, with the long flashes indicating the 10's (count them) and the short flashes indicating the 1's . Write these codes down and look them up in your Chiltons manual. Assuming you have manual part number 8259, the codes for your car are on page 4-54 on the top of the page. There may be several codes stored, so keep watching and writing down codes until the CEL stops flashing. When you have all the codes recorded, unplug the negetive battery terminal for a half hour or more (overnight is good). Then start it up let it idle for 15 minutes then take it for a really nice drive around block like you are breaking it in. Shut it off then drive it like normal. When you are done, you will need to reprogram the clock and radio presets, of course. . . If you post the codes here, we can help you diagnose the problem as well.




#12 cookie

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Posted 29 December 2004 - 12:14 PM

an extreme cold start I agree with checking the codes and I like setright's idea.
I also tend to wonder about the temp sender as that can cause a hard start if its out of spec.

#13 jeansain

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Posted 29 December 2004 - 02:54 PM

Thanks for the replies everyone.

I disconnected the battery for a couple of hours and re-connected it and that solve the problem... hopefully for good. If it happens again, I'll the have the codes read.




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