P0170 Fuel Trim - Things to look for?

CEL came on this weekend while driving at high elevation (6-7K) on a camping trip.

 

Already have a new front denso O2 sensor (15.5K/1.5 year old)

Fuel filter was last replaced in Dec 2010 (27K ago) w/ OEM

Spark plugs & wires last replaced 26K ago w/ NGK

 

Getting 20-21mpg city and 26-28mpg highway.

 

I've reset the code for now, but would like to start troubleshooting in the meantime. Any ideas or things to check would be appreciated. Thanks!

Well, the code came back.

I inspected some of the OBD2 values at idle:

 

Long term fuel trim: +27.34%

MAF 3.02g/s and 1.10 g/s

Coolant 71C, 83C, 89C

Intake manifold pressure 28.10inHG, 31.15KPA, 31kPA

http://www.obd-codes.com/p0170

So I think that confirms I have a perceived rich condition.

 

I believe I have an exhaust leak - I occasionally hear a whistle/hissing type sound above 3K RPM and have ordered new fel pro exhaust manifold gaskets (MS 97055). For $10, I guess that as good a place as any to start.

be fore you unbolt the manifold bolts, (they can bust.)

listen for the ''hiss' farther back at the spring bolt connection.

that donut can and will hiss when it starts to leak.

and i think that is more common.

but that leak would not throw a code.

 

i would look for a vacuum leak or an intake leak.

buy a can of carb cleaner or starting either and spray it around the intake and vac lines.

if the engine surges, it is sucking in the spray.

that's your leak.

 

have you removed the intake or any part of it recently?

No, I have never removed the intake. I've taken off the TB and replaced the PCV, but that was at least 2 years ago.

 

Found a intake leak on the EGR. If I spray carb clean on it, the engine surges. Going to try cleaning it in case that helps

Ok, long term fuel trim is down to 14.8 now, which seems to fix the CEL, but it's idling like poop now. Sputters a lot. Turning on the rear defroster/AC at the same time disrupts the idle for like 30 seconds before it stabilizes. IAC needs a cleaning too?

 

What confuses me though, is this wasn't an issue before..

 

Only things I changed were:

*Cleaned EGR valve (put button half in chem dip for a few hours as the spray can wasn't good)

*Re-positioned the car without the EGR in (ran like crap, of course)

*Installed reman OEM alt

OK, I cleaned the IAC & replaced it's gasket. Long term fuel trim down to 9.6%, but the idle is worse now, it's even stalled a few times at stoplights. It's rough in park, neutral and drive.

Hello;

Check the output voltage on the mass airflow sensor. Mine went south causing a bad idle. Also check for any vacuum leaks, and the air intake tubing. Steven.

How do you do that? Do you use a multimeter? I measured 3.02g/s and 1.10g/s from my OBD2 scanner

Hello;

Measure the voltage(DC) on #2 terminal(white wire), this should be .8-1.2 volts. I have a old vtvm that I use, but a good vom or dmm should work. Pierce the wire with a straight pin and measure the voltage. My maf voltage would spike up after the car was warmed up causing an uneven idle. You can also check the O2 sensor using this method, Steven.

I did another run with the OBD2 sensor plugged in. Did a loop around my neighborhood, varying speeds from 25 to 45mph. Even floored it for a little bit. Car was warm at the start, but still had a rough idle. I've uploaded two charts from the drive in the hopes someone can help me analyze them.

 

Thanks!

Thought I'd follow up. I solved this by replacing the MAF with a used MAF off eBay.