135-155-171-174

[eric k]

I have a 96 4.0 ranger. Going through emissions right now and so far I've replaced the purge valve and flow sensor, egr valve and tube, and dpfe. Cleared up all those codes. Still have the 135-155-171-174. Read that I should clean the Maf sensor. Any other ideas to clear up these codes? Thanks

 

[eric k]

Update:
Got rid of 135/155. Fuse was bad. Now all I have left is the dreaded 171-174. Noticed today when I let off the throttle it continues to rev for 5-10 sec then will have an up and down idle 5-10 sec then idle perfectly fine. Any input is appreciated. Thanks.

 

[4.0blue98]

Not saying this is it but check this out.

http://www.performanceprobe.com/ind...rmanceprobe.com/misc/tsb.php?article=98-23-10

I had intermittent idle issues and p0171 and p0174. Seemed to come and go. Tried cleaning the MAF with MAF cleaner as per can instructions and it would help briefly. MAf looked sort of dirty no matter what. Also had terrible knock and ping under load regardless of octane. Just replaced MAF and so far so good.

 

[iceman.kcmo]

With the idle doing what it is and IIRC those codes are Lean codes, I would say you have a vacuum leak.. Get some starting fluid and start spraying..

 

[RonD]

Yes lean condition Code on both banks means the computer has richened the mix as far as it can and mix is still too lean.

I would not suspect an O2 sensor issue since both are showing lean.

Unmetered air would be the next place, and it doesn't have to be a vacuum leak, just unmetered air, so a crack in the air plenum can let in air that the MAF isn't "seeing", but I guess technically that is a "ported" vacuum leak, lol.
MAF data sets gross fuel/air mix, then O2 sensor data fine tunes the mix.

And yes the RPM not dropping with throttle would suggest an air leak.
Try disconnecting the IAC valve while engine is idling, on a warm engine idle should drop to about 500 rpm, now rev up the engine and see if RPMs stay up even as throttle closes, if not clean the IAC valve.

Make sure PCV valve is clean and fits tight, also Power brake hose is good.

Use some injector cleaner in the tank.
Make sure fuel pressure at the rail is 30-35psi, computer opens injectors based on 30-35psi, if pressure is 20psi then computer can't open them long enough to get correct mix, so lean condition is seen.