Subaru Forester -- check engine light, flashing cruise control, misfiring cylinder, rough idling

I have 2006 Subaru Forester that is idling roughly. 90k – oil change every 3k miles. Per diagnostic codes I learned that the 2nd cylinder was misfiring. I replaced the coil, spark plugs, ignition wires, and an airflow sensor. Yet, my car still idles rough. The check engine light is solid and the cruise control is flashing. The idling problem only happens when stopped… after I get high rpms there is no shaking. I had someone disconnect the battery and reset the computer and the lights stayed off for about a week and idling was fine. Week later – the problem returned. I think this an electrical problem, but not sure if mechanical. Any thoughts?

It might be a good idea to check the compression on all cylinders. It’s possible that No. 2 could be misfiring due to a tight valve and it’s always best to weed out any mechanical issues before replacing anything.

It could also be a bad head gasket.

Being that it runs ok when you have your foot on the gas and idles rough when its off leads me to guess a vacuum leak of some sort. Check that every single hose is connected tightly and theres no small cracks or dry rotting. Look around your throttle body.

The other possibility, although im slightly leaning towards it not being this - a bad IAC.

Using a vacuum gauge might help pin down an engine problem also.

You need to get the codes read again. If you do then post them

Although I am mechanically challenged on post 1976 vehicles I would guess valve problems. My 1971 Mustang 250 cu in inline 6 cylinder suddenly started to idle so rough it was shaking itself apart in 1981. It was normally smooth on the highway. I did a compression test and 2 cylinders were dead. When I pulled the head 2 exhaust valves were very badly burned due to a head gasket air leak. I took the head to a local machine shop and was treated to one of those rare lucky moments. The owner of the shop had a completely rebuilt head with brand new valves, springs, rocker shaft, rocker arms, and pushrods, A customer had brought it in more than a year earlier and never came back. He sold it to me for his parts cost $85! It went another 50,000 miles until I sold it with no problems!

Our 06 Forester LL Bean edition bought in 07 with a couple thousand miles on it and at 51000 now has been having this cruise control light/check engine light issue for couple years, Dealer just keeps saying its the gas cap. Never offers to check it out. Same nice guy that charged over $2300 for head gaskets on my 02 Impreza. We have replaced gas cap, most of exhaust system, and its still on again.

" I had someone disconnect the battery and reset the computer and the lights stayed off for about a week and idling was fine."

There’s the mystery. Have the computer reset again. If runs perfectly fine afterward for a few days like before, then reverts to bad running, I’d be looking at the PCM (engine computer).

@bobcu174, maybe providing some info about any codes that were set could lead to some assistance on this forum.

You state the dealer says it’s the gas cap but never offers to check it out. The question is not whether they will offer to check it out; it’s whether or not you will authorize a diagnostic and any associated labor charge to do so.

My assumption, right or wrong, is that by use of the word “dealer” you mean the service desk person. Few of those people can ever offer a reasonable diagnosis as most have never worked as a mechanic.
At least with a roomful of monkeys pounding on typewriters there is at least a faint chance they could eventually pound out some decent literature… :wink:

At least with a roomful of monkeys pounding on typewriters there is at least a faint chance they could eventually pound out some decent literature...... ;-)

There’s the problem. The dealer usually has only a few “service advisers”, maybe if they had a couple hundred we’d stand a faint (albeit very, very, faint) chance of getting the correct work done on our cars. LOL

Note to bobcu174; had this problem w/ a 2007 LL Bean Forester. It was the check valves mounted on top of the fuel tank - plastic parts that degraded, leaked and generated the emission code. PIA to change because you have to drop the tank.

Take the car to Autozone or Advance and get the codes read and report back.

has the accelerator stopped working?

I have a 2007 L.L. Bean Edition Forrester. The cruise light is flashing and check engine light is solid. I am well into my retirement age and nearest dealer is about 2 hours away. Is this something that local mechanic can fix? He is very good, but not Subaru schooled. Help, I’m afraid to drive it now.

@kansasgirl - you need to start a new discussion on this. Copy what you wrote, then click on the “New Discussion” button (top right) and paste it in, with an appropriate title.

I had a similar problem with the flashing cruise control and check engine light. Had a scan done at a local repair shop. The problem was a faulty stoplight switch. The complete list of symptoms included: - check engine light on
- cruise control light flashing
- brake lights not working occasionally
- shifter stuck in park occasionally. Needed to use a screwdriver to push in a release mechanism beside the base of the shifter.
I was told all of these problems were related to the faulty stoplight switch.
Everything is working fine… for now.

I had a similar issue on a completely different car (Lexus is300) and it turned out that the battery was failing and I guess not supplying enough energy to operate things at very low engine speeds. On my car the stability control flashed and something else, not the check engine light, was on. I bought a new battery from Costco, and it fixed everything. And yes, I did clean the terminals really well first, and it did not help.

The bottom line of this thread is that the car needs to be diagnosed by a competent mechanic ASAP. Driving it this way may very likely be doing further damage, even though the CEL is not flashing.

Any good shop will likely start by downloading the stored fault codes. In addition, they’ll very likely do a compression test, a leakdown test, and if they haven’t nailed it down by them they’ll probably put the engine on an ignition analyzer to check the spark out. They’re probably going to ask you questions about your oil usage and operating problems as well, and they may test the coolant for evidence of hydrocarbons.

My guess is that somewhere in the process of the above actions they’ll find out exactly what your problem is and ask you what you’d like to do from there. Post back and let us know. We do care, but this needs to be looked at hands-on.

Agree with you mountain bike, in addition many newer model vehicles (especially subarus) will flash the cruise control light to warn that it will not function with the check engine light on and the engine running poorly