I own a 1998 Ford Ranger XLT with the 3.0L V6 5spd. manual transmission with 87000 miles. Recently the engine has been acting up at idle. The engine runs extremely rough and even stalls. It almost sounds like there is a 3/4 cam installed the engine is runnning so rough at idle. At operating speeds the engine runs relatively well. Upon deceleration at highway speeds in 5th gear, the truck continues to hold its speed a few seconds after letting off of the accelerator. One other potential clue is a whistling sound like a diesel engine turbo between 1,000 to 4,000 RPM.

The check engine light recently came on and scanning the codes revealed error codes #171 and #174, corresponding to lean fuel/air mixtures in both the left and right engine banks. My initial thoughts are possible vacuum leak, idle control valve malfunction, O2 sensor problem, or Mass Air Flow Sensor issues.

Any insight into helping me narrow down my problem would be greatly appreciated.

Thank you!

Andy

 

Hi Andy, welcome to FTE!

I think you are already on the right track. Vacuum/exhaust leak is at the top of the list regarding the lean codes, but I agree you should also clean your MAF and maybe change your fuel filter and run some good fuel system cleaner through. Have the original spark plugs and wires ever been replaced?

As for the lousy idle, that could be caused by the same thing that is causing the lean condition, or it could be a bad IAC valve. You can try cleaning the IAC but if that is what is causing your bad idle, you will probably need a new one.

 

The fuel pump was recently replaced, it up and quit one time while running down the highway. The plugs and wires have both been swapped out. I was also thinking about the fuel filter, thinking lower pressures at idle could be causing some of the problem. Before reading your reply, I did take off the Idle Control Valve and tried cleaning it. While at idle after the cleaning the engine seemed to run a lot better if I tapped on the ICV lightly with a hammer. One quick question is whether or not the ICV cycles open and closed at idle, or does it remain open all the time?

Thank you for the response. I'll be swapping in a new ICV tomorrow morning sometime. I'll let you know how it works out. The only thing that really makes me think sensor is that this problem has seemed to occur overnight, not something that progressively got worse (fuel pressure issues) or was intermittent (partially failing solenoid valve).

 

I forget to mention, an EGR system that isn't functioning up to snuff can cause erratic lean/rich conditions, too. Something else to keep in mind.

Keep us posted.

 

I was also thinking EGR. Look for the whistle, that will be your vacuum leak. Could be a leak in the EGR.

 

For Those of you following this Topic, here's what the problem turned out to be:

If you guessed Vacuum Leak, DING!! DING!! DING!!Congratulations!!! You were right.

It turns out that during the last oil change the owner of the vehicle, not myself thank heavens, knocked the GIANT vacuum hose underneath the cruise control unit off of its port. That would explain the error codes, and the "turbo-like" whistling, and the rough idle.

I spotted the dangling hose when I was underneath changing out the O2 sensor on the passenger side of the vehicle. I wasn't able to get a look at the open vacuum port until the truck had been pulled up on the ramps which changed the angle I was looking into the hood compartment.

Thanks for the info. What a bone-head error huh?

 

Glad you found the problem.