Hi, A few weeks ago it started to get cold where i live. On about the first day that it was starting to get cold my check engine came on. I checked the codes and found p0171 and p0174 (system too lean). I erased the codes but they came back the next day. I erased them again and again but they always come back. I also noticed that as it became colder my engine idled eradically. Today when i was comming up my driveway my engine stalled. I was thinking that there could be a vacume leak but it only idles weird in park and neutral. It idles fine in all other gears , even at low rpm. I am thinking that it might help if i changed the fuel filter. I don't think it has ever been changed. It wouldn't hurt to change it so i probably will. I am also thinking that there could be a problem with the idle air control valve. but i don't really know much about this type of thing.

thanks,
CAW

 

do you have an intake? drop in K&N ?

 

Yes, I have one of the reusable K&N air filters

 

do you know for sure if you have a IAC?

 

I'm sure that i have one.

 

take it off and clean it with electric parts cleaner, same with the MAF, just spray them down and let them dry

dont touch them.

 

mine does too it didnt want to start today after school, but started fine this morning

 

I just checked the MAF. The 2 wires and everything els looks clean. I am going to check the IAC next. If i take the IAC off will that hurt the gasket between the IAC and the intake? Or is there even a gasket there?

 

no it shouldnt, mine came right off, but mine is newer

 

mine is a 93 when i took mine off the gasket fell right off and all together and was in perfect condition. So i am guessing yours should come right off to. But i read that the iac is not supposed to be cleaned but just replaced.

 

it can be cleaned with electrical parts cleaner. the reason for bad idle and dirty parts is the k&N filter, put a stock filter on and replace those sensors you proly wont have that problem agian.

 

Alright, i think i've found it!!!!!!!
I took off the IAC and noticed that i could see light comming through the valve. My shop manual talks about testing the electrical stuff for the IAC. It said that the connector should read about 12V when the key is in the on position. I got out the volt meter and read about 12V. Then, I connected the IAC to the connector. Nothing happened . Since the IAC is opperated by a solenoid it should have closed or at least clicked. Now i am almost sure that's it. That would explaine the trouble codes too!

 

Well, maybe that not it. I unpluged the IAC while the motor was running and it almost stalled. It seems to be getting worse. Today it stalled again. And almost stalled a few other times at stop signs.

 

^ is the motor supposed to stay running when it is unpluged? i dont see how it would since that controlls the idle... Unless it is supposed to stay at the same rpm's.?

 

When I replaced my stock throttlebody with a BBK 66mm throttlebody.... I started the vehicle with the IAC power disconnected.... The engine should idle at approximately 450 rpms. There is an adjustment screw on the throttle linkage that allows for this adjustment. When the IAC is plugged in and working correctly... the idle rpms should be approximately 750 rpms.....

OR 4x4

 

Heh, this seems to be a common problem that none of us can find the answer to.

Ok, after several weeks worth of dealing with the same problem, this is what I've found.

First, a p0171 and p0174 - can be, and usually are caused by a vacuum leak - most notably the PCV tube cracking.

Second - a dirty or bad MAF - clean with electronics cleaner, or replace.

Third, dirty or clogged injectors or fuel lines, improper fuel flow.

My guess is, based on the fact that after reading through, most of us seemed to have recently changed the fuel filter or needed to change the fuel filter, this lean condition is going to be something in the fuel system rather than electrical.

I'm still trying to diagnose and solve the problem, and I'll let everyone know what I find out.

 

I've done some more investigating and am now thinking that it is the IAC. I took it off again and hooked it up to 12v. It made a clicking noise but the valve didn't move at all.(i made sure that i hooked it up right so i didn't burn up a diode). The valve part was covered in carbon deposits or what ever it is. My local auto parts store wants about $35 for a new valve so i'm going to try one. I'll let you know how it works.

 

The IACs that I've taken apart were clogged with carbon. Gum-out solvent is what I'd suggest. For the MAF, use non-residue contact cleaner only. Any oil or residue (like bleaching from acetone, oily film from naptha, etc.) can permanently ruin the sensor.

Also check the very rear of the intake manifold for a 4-way vacuum plug, threaded into the manifold, and with 4 or so vacuum hoses of various sizes attached. I've seen other threads where the brass fitting broke, the tubes had popped off, and sometimes there are rubber caps (not hoses) that blew off because of back-fire.

Check the EGR tube for a crack. If it's lean, it's probably a vacuum problem.

 

Got it fixed!!!!!! I replaced the IAC valve and it runs great. Thank you all for your help.

 

Told ya
Good job bud