Running lean

[SHO Continental]

my '93 is getting a 176 and 172, running lean on both banks. The codes pop up with street driving mostly. Replaced the fuel filter 4K ago. Also checked the fuel press, was running at 32psi at idle, 40 at WOT or with the vacuum out. I guess that's the normal psi? Using 91 octane. Any suggestions?

 

[NotSoSlowSHO]

more than likely a true lean situation.

I would start looking for vac. leaks....

 

[jedhead]

Maybe your injectors are dirty.

Bob

 

[jaded93atx]

Your IAC may be stuck open letting in air past where the MAF can meter it. It wont throw a code directly pointing to the IAC. You may want to try cleaning it thouroghly with some plastic friendly carb cleaner, make sure to move the internal plunger thing back and forth to get the gunk that accummulates on the shaft underneath. Just hosing it down wont do the trick.

 

[NiNeTy Fo SHO]

If it was your IAC, the MAF would be reading it as the MAF is before the IAC.

I would try cleaning your MAF...if the contacts get dirty in it, it will not read correctly...aka saying not as much as is coming in as there really is causing the computer to reduce the gas going into the engine causing a lean situation. I would try this and checking for vac. leaks as mentioned above.

In theory both O2 sensors could be bad also...just the chances of them both going bad and reading lean close the same time are quite small.

 

[jaded93atx]

Right....the IAC is AFTER the MAF therefore if the valve is stuck open then it lets air in that is NOT metered by the MAF... essentially a vacuum leak. I had it happen to my 93 ATX. I cleaned the MAF, changed O2's, checked everywhere for vacuum leaks, and finally replaced MAF but to no avail. My O2s may or may not have been bad I dont know but they only had 10000 miles on them and probably only 5000 when the 172/176 codes began. After I replaced the O2s I started getting only a 157 MAF code and after almost a year of frustration, poor driveability, and horrible gas mileage I pulled the IAC and bench tested it with a 9 volt battery and could feel the solenoid try to move the plunger but it was stuck. I cleaned and replaced it and no problems since.
BTW I had attempted to clean the IAC a couple of times prior but only hosed it down and that wasnt enough.
The other advice is also very good and are very possible reasons for your lean condition and not to be overlooked. I'm just stating my solution to my lean condition and how I resolved it.

 

[NotSoSlowSHO]

Right....the IAC is AFTER the MAF therefore if the valve is stuck open then it lets air in that is NOT metered by the MAF... essentially a vacuum leak.

Read what you just posted.

Then realize that the air provided to the IAB Idle Air Bypass valve it metered.

A stuck IAB will not result in a lean condition, unless the IAB to intake gasket is bad.

 

[jaded93atx]

Yes the air coming through the throttle body to the IAC is metered, but the air that can come through the that plastic capped valve thing on the top and outside of the IAC is not. If you have the IAC off and blow into the chamber air will escape through that valve when its open and that can be a source of unmetered air entering the intake ...ie a vacuum leak! Jeez

 

[NotSoSlowSHO]

Yes the air coming through the throttle body to the IAC is metered, but the air that can come through the that plastic capped valve thing on the top and outside of the IAC is not. If you have the IAC off and blow into the chamber air will escape through that valve when its open and that can be a source of unmetered air entering the intake ...ie a vacuum leak! Jeez

The IAB does NOT breath thru that cap.

And Im happy it does not. It wouldnt only be unmetered, it would be unfiltered.

 

[zpyro]

as NotSoSlow said, air going through the IAB is not unmetered, because in order for air to get there it has to go through the MAF and is therefore metered. even if the IAB was stuck open, the extra air that goes through it is STILL being measured by the MAF and, therefore, cannot create a lean condition

 

[jaded93atx]

Allright then, you all must know better then me, but I'm gonna have to stand my ground , I may not know why or how but my IAC was causing my lean condition. I was getting about 15 miles to the gallon and 172/176 along with a 157 code and poor driveability. After testing, cleaning, reinstalling it and nothing else my mileage went to around 30, no codes, and it drives like a champ. That was about 8000 miles ago. As I said, prior to that I had tried everything and even tested the IAC gasket for leaks by using water, propane, and then carb cleaner . If the "breather" wasnt letting air in then somehow the stuck plunger was causing the condition some other way. I know I'm not a licensed tech and I dont have 3000+ posts but I know what worked for me. To each their own.

 

[nik97]

IAC/IAB--No. Injector problems- probable. Vacuum leak- most likely. If possible, a smoke test will reveal hard to find vacuum leaks. Also don't overlook a possible pre-02S exhaust leak/hole causing a false lean situation. --How does the car run??

 

[SHO Continental]

IAC/IAB--No. Injector problems- probable. Vacuum leak- most likely. If possible, a smoke test will reveal hard to find vacuum leaks. Also don't overlook a possible pre-02S exhaust leak/hole causing a false lean situation. --How does the car run??

Car runs.. slow. I'm leaning towards vacuum leak from when the motor was just hanging, did a subframe swap last week.. I'll look into it tomorrow

 

[jaded93atx]

That deffinately should have been mentioned...all I said forget it, unF&* ^$#@real!!! You did a subframe swap and had the motor hanging but didnt think that may have been a critical matter in diagnostics of a lean condition or possible vacuum leak? Again unf%$#@!* real. You're an idiot and I/we are bigger idiots for trying to help you!

 

[SHO Continental]

yeah I didn't think it was a big deal.. put 200 miles on it after the swap before the CEL came on, I'd think if it was a vacuum leak or something else caused by the swap that it would have shown up right away.

 

[SHOtimer]

That deffinately should have been mentioned...all I said forget it, unF&* ^$#@real!!! You did a subframe swap and had the motor hanging but didnt think that may have been a critical matter in diagnostics of a lean condition or possible vacuum leak? Again unf%$#@!* real. You're an idiot and I/we are bigger idiots for trying to help you!

I think that was a bit extreme. A vacuum leak is a vacuum leak, no matter what the cause was/is.

Doug

 

[Sh03d]

That deffinately should have been mentioned...all I said forget it, unF&* ^$#@real!!! You did a subframe swap and had the motor hanging but didnt think that may have been a critical matter in diagnostics of a lean condition or possible vacuum leak? Again unf%$#@!* real. You're an idiot and I/we are bigger idiots for trying to help you!

 

[nik97]

jaded93atx,
--Ouch! Speak for yourself. This stuff should not be taken so seriously

SHO Continental, That sounds like a vacuun leak for sure. That reminds me of when I thought my IMRC motor took a crap because my car was guttless. After checking the fuel pressure, MAF, INJPW, TPS and other parameter values I fugured I should clean my MAF because of the irregular value I was getting. On my way to remove it I noticed my intake plumbing had sepatated from the TB considerably causing gobs of false air. Easy to overlook the simple things!

 

[jaded93atx]

Your Right and I apologize... Mom always said if you dont have anything nice to say dont say anything at all.

 

[F-22 Raptor SHO]

Your Right and I apologize... Mom always said if you dont have anything nice to say dont say anything at all.

My mom would say if you talk like that to anyone ever again, I will ground you till the cows sprout wings and fly home.