I'm working on a friends car he has a 1998 s70 2.4l non turbo, Ive put a lot of work into replaced struts ,motor mounts, spark plugs, wires, cap and rotors. Anyway the main issue I am having is that after 30 minuets of driving the car idles rough when stopped and dies. I used a scan tool and from the readings im getting no matter what rpms the lt ftrm1 never changes always stuck on -12.5% the st ftrm1 is looking normal usually + or - 5% from 0. Any clues or ideas why it doesn't fluctuate at all? I did clean the maf (mass air flow sensor) and it seams to run better, it would idle rough when coming to a stop but never die. Im just concerned because i would assume that if the maf was bad the lt ftrm1 would show some kind of change or am i wrong? Also their was a p0171 code and a evap leak. I reset the codes and drove about two hours yesterday and no codes have come back as well as no pending codes.

Thank you for your time, Brian

 

Fixing the leak didn't correct the rough idle? When I had a rough idle, I had a leak at my idle control valve. You should check those vacuum elbows real good. At this age they get holes in them and leak air. They do cause codes like the P0171 as well. Not always show up within 400 miles.

 

The long term trim is basically a record of what your car is trying to adjust in order to balance your fuel/air mixture.

Having a consistent long term trim at -12.5% means that your car is LEANING out your mixture by 12.5% (if not more) when compared to the factory pre-set level. This means that the car wants to run REALLY rich, but the car's computer is doing everything it can to adjust the mixture lean to be as close to normal as possible.

How do we know that the car is running rich? If the first half hour is better than the next, it means the engine runs better when cold. An engine is only happy running rich when cold, and will bog down with too much fuel when warm... that's consistently rich, and something is keeping one of your systems from making the injection system adjust when necessary.

The question is: why? What is making the car run so rich? There are 3 major causes.

1) MAF sensor, but you've already said that isn't your issue.
2) Air intake. How old is the air filter? Has the car been in storage? Mice LOVE the 3" intake tube as a place to nest and raise families.
3) (Most likely) Clogged catalytic converter. It restricts airflow out, which restricts airflow in. This is usually the cause.

 

Well i cleaned the maf sensor again today and it helped some now its stuck on -7.8 and changes specialy when driven hard other than that no change where it wasn't doing that before. I keep thinking about the air filter but i recharged it and has been clean. Catalytic converter is a good idea, his car has almost 230,000 miles. Wouldn't that trigger a code as well?

 

Sorry mobile version wont let me fix errors darn t9. Will fix when i make it home.

 

What about a broken thermostat? Is temp gauge pointing right at 3PM? If it doesn't come up to 3PM in about 5 minutes or less, then you need new thermostat.. ..and that will make run rich too.

 

Yep right at three.

 

"I keep thinking about the air filter but i recharged it and has been clean."

This statement, had it been included in your original post, would have led to a much quicker solution.

Your MAF is shot.

Oiled air filters are death for the MAF sensors in these cars. The reason for this? The wire element of the MAF heats itself from time to time in order to burn off contaminants and maintain a pure reading of the intake air. As air rushes through your trusty K&N, the force of the air rush makes tiny droplets of filter oil to break loose from the cotton and fly through your intake. 1 in every 1,000 of these oil droplets lands on the thin wire element of your MAF sensor. When the element heats up, the filter oil cooks and forms a caustic coat of oxidizing char.

If you buy a new MAF, your problem will be solved. If you use the new MAF and leave the oiled filter in your air box, your problem will come back. When? I don't know... But I assure you it will eventually.