1997 I30 - P0174. Bad MAF?

[vonscorpio]

I’ve got some new/worsening issues with my I30.

The history: the car has previously exhibited the “cold start, then die” symptoms, which I addressed by cleaning the mass air flow sensor (MAF) and replacing the fuel filter. After that operation the RPM was notably lower than usual, and it still didn’t solve the cold start issues (as mentioned in one of my previous posts, the car runs just fine after you tap the gas to get it started). I just had a friend replace the valve cover gaskets/spark plug tube gaskets, spark plugs and plenum gasket. Haven’t gotten around to cleaning the IACV or throttle yet.

After that operation I’ve had two new issues: the idle dropped even farther and the gas pedal “freezes” in resting position if it sits long enough. A solid tap gets it loose, but if you aren’t ready for it the extra pressure it takes when it sticks could launch you forward. The day after I was sitting at a traffic light and the RPM dipped and the vehicle started stuttering like it was thinking about stalling and the check engine light came on: code P0174 (bank 2 I believe). Few days later it stalled at idle. Drives fine otherwise.

Since I tried cleaning the MAF, I am inclined to believe I messed it up somehow. The symptoms are becoming identical my M30 when it’s MAF failed. All the O2 sensors are new, so I am less likely to suspect them—although the one right in front of the passenger firewall (the annoying one you have to pull off the front right wheel and wheel well to get to) was getting dripped on by the oil leak prior to the valve cover gasket job.

So, here are my questions:
Anyone familiar with possible root causes of a P0174?
Should I just replace the MAF and be done with it?
And possibly the biggest safety concern, is there a safe way to lubricate the throttle cable/fix the sticky pedal?

[IAMTheRuckus]

There could be a few reasons for that particular code. It's a left bank lean code and could be caused by exhaust leak, intake leak, injectors, fuel pressure (fuel pump, or regulator), 02 sensor, or MAF. I think fuel pump could be ruled out because its only occurring at one bank instead of both but that still leaves quite a few items to check. You'd have to test fuel pressure and voltages at each of the items mentioned to check for functionality.
Check for exhaust leaks
Check for intake leaks
Check continuity at 02 sensor
Check fuel pressure
Check voltage at MAF
That's how the flow chart is set up in the FSM and what I would go by if I were diagnosing this at the dealer.
As for the sticking throttle cable, try cleaning the inside of the throttle body and see if that helps. Probably just built up crud around the throttle plate.

[NutriaforBreakfast]

Check several items and don't just assume something is the root cause right out of the hat

Pay particular attention to the throttle body
Want to get all crud off of the butterfly itself (front and back) and well as where the butterfly seals around the throttle plate
Don't go crazy with the carb cleaner-just spray it on a rag and wipe. I have had better luck with rubbing alcohol and it doen'st
mess up electronic stuff
Lots of ghosts to check with this problem

Yes after the car gets older all that plastic air plumbing can easily let in air leaks

Also check the fuel regulator
One check is to see if gas comes out of your fuel regulator when you pull of the vacuum hose

Both of my maxima's ran better when I removed the MAF sensor wires when the car was running
That was one way I figured out the MAF was bad
Not a complete check in itself but a good start toward diagnosis

If none of this works, I would look at my emissions items like EGR, PCV, and idle air control valve
You can check the EGR valve quickly by pushing up on it when the engine is hot
If the engine DIES, then the valve is ok

[vonscorpio]

Thanks for the advice on this. I had a bit of time to look and listen last night.
There is an audible hiss which I assume is related to a vacuum leak of some kind. I couldn't isolate exactly where it was coming from. It didn't seem very affected by engine RPM. It sounds like it was coming from the area near the throttle/PCV valve and hose, but unsure (I am aware this is on me, since its tough to convey via text the location of a vacuum leak).

As for the throttle, without taking anything apart, it almost looks like the gasket might be disintegrating and possibly interfering with normal operation. Problem is: I can't find throttle gaskets for sale locally. Is "cut to fit" a good idea?

[vonscorpio]

Update in case someone else has similar problems: throttle gasket had indeed failed, and air was getting past. The pedal stickiness was due to carbon build up on the throttle itself (just as NutriaforBreakfast said), which cleaned up nicely.

Cleared the codes and engine is back running as normal. Thanks again everyone!