99 Q45 CEL - Please Help!!!

[Brody77]

Longtime reader, first time poster. I just want to say I'm very grateful this site exists. Lots of helpful information here for Q owners so thank you to everyone.

I've got a problem with my 1999 Infiniti Q45 that has me extremely frustrated. I've wanted a Q45 for a long time. My parents owned a 1996 Q45 for years and put over 250,000 miles on it with literally zero problems outside of normal routine maintence (tires, brakes, shocks, etc.). That experience, combined with what I've read from credible automotive sources about their longterm quality and reliability made me comfortable purchasing this vehicle the way I did, which was:

I found the car on the Internet at a Honda dealership in St. Louis (about an 8 hour drive away). It was a one-owner local trade with 127k miles. Clean CarFax and fairly extensive documented service history including recent transmission service, new valve cover gaskets, fuel system service, new O2 sensors, regular oil changes/lube, etc. It appeared to be in good to excellent overall condition inside and out and also had just had 4 brand new Goodyear Assurance tires put on it. They only wanted $4,995 and I got them to accept $4,500 so it seemed like a deal just too good to pass up. My gut kept telling me it was a deal that seemed a little "too good". But I went ahead and bought it anyway and had it shipped here. When it got here last week it appeared to be everything represented and if anything even better. Looked great, ran and drove great, no problems. That lasted about one day.

The next day while drive the Service Engine Soon light popped on. Read the code and it came back "P0174 System Too Lean - Bank 2". Knowing this could be caused by any number of different things I started with the most basic and least expensive and worked up from there in the following order:

#1. My first step in my process of elimination was some sort of vaccum leak. Pulled the engine cover off and inspected carefully for vaccum/PVC leaks. Didn't find anything (at least not anything obvious) as far as vaccum leaks.

#2. Second, I wanted to address the possibility of any plugged/dirty injectors. Pulled the air intake boot and inspected the throttle body and butterfly valves. They were pretty gunked up with carbon but not overly extreme for the age and mileage. Got a can of SeaFoam Deep Creep and ran it through the throttle body at 2500rpm. The car smoked like a Bar-B-Cue and this seemed to clear it out pretty good. Also, filled it up with 91 and mixed another can of regular SeaFoam in with the fresh fuel to address in any inline fuel system issues. Started better and seemed to have better throttle response. Cleared the code. Next day CEL is back on - "P0174 System Too Lean - Bank 2".

#3. Third, I addressed the MAF. This is what I suspected all along but was eager about doing anything with the MAFS. I hate those things. However, the air filter was absolutely filthy. It was a Nissan OEM, but it was black with grime and oily to the touch. When I saw that I figured I had the problem licked. Figured the MAF was dirty and that was causing the ECU to trim it out too much. Got me a can of MAFS Cleaner at NAPA, pulled the MAF out, carefully sprayed both side well, let it dry, stuck it back in - no start. Engine would crank but not start. Checked my fuses and saw my EGI fuse was blown. Put in a new EGI fuse, uplugged the MAF, and it fired right away. Right then I knew I somehow toasted my MAFS. 2 days and $300 dollars later I put in a brand new OEM MAFS. Figured while I had the engine bay tore apart I might as well throw some new plugs in it. So also I installed 8 new OEM NGK Platinum plugs as well. Put it all back together and the car ran great, no CEL, and I figured the problem was fixed.

#4. Tonight - after driving it for 3 days with no problems - I come home from work and my wife tells me the CEL is on in the car. Went out and read the code - "P0174 System Too Lean - Bank 2". At this point I'm looking around my garage and read to take my two 5-gallon gas cans and the extra propane bottle for my grill put it in the front seat and throw my lit cigarette in it.

I'm really starting to hate this car. On top of this apparently unresolvable CEL light, the car emits a strong odor of burnt oil after driving it for a while. You can smell it both from the outside near the engine (not the tailpipe) and also inside the car through the heater vents. However, the car doesn't appear to be using any oil. I've put about 800 miles on it now and the oil level hasn't dropped a milimeter. It also doesn't smoke at all. My theory is that the oil smell is coming from the previously leaking valve cover gaskets (that have now been replaced) leaking oil onto the sides of the engine block and the exhaust manifolds. When I had the engine bay torn apart to do the plugs and MAF I noticed a pretty good layer of old oil from the previously leaking gaskets covering the sides of the engine. But that is just a theory.

Finally, I've also noticed the interior appears to have been spraypainted with some kind of interior spraypaint. The leather seats seemed harder and stiffer than they should be to me so when I moved the seats all the way forward or all the way back I noticed overspray like from a spraypaint can the same color as the seats on the lower portion of the center counsel, on a couple of the seatbelt connectors, and also on the metal driver's side floormat clip. Not sure if this is just something dealers do to make the seats look better or representative of a bigger problem.

None of that concerns me as much as this CEL. The fuel economy is terrible and the cars seems to have a funky kind of up and down vibration while in drive with the brake on (like at a stoplight). I'm fairly sure this is releated to the lean condition and the engine being starved for fuel. Any advice or pointers would be very much appreciated and I apologize for the length of this post - just wanted to make sure everyone had the most complete picture. Thank you in advance.

[BadQ45t]

Well I can tell you that you shouldn't have these issues if the car was indeed in the kind of shape that you thought it was in. My 97' has none of these issues, but I have owned since 2000 and I baby the hell out of it.

I think you need to find a good Infiniti Mechanic, get him to assess the codes your getting and the real condition of the car. I would say you can cut your loses quickly and sell it for about what you paid, spend 7k and get a much nicer 2000 Q or even a 3rd Gen are starting to show up around that price point.

The car started life as a very reliable car. I have had nearly zero issues with mine and the leather is soft, there are no weird smells and my only CEL was for an O2 Sensor. So if I were you I would do a quick assessment, and either fix it up or dump it quickly. You should be able to get your money back I would think easily.

Last question, where are you located? Maybe someone can chime in with a good shop reference.

[Lokim]

Get yourself a can of carb cleaner and start spraying it around the intake tube (post-MAF), plenum gaskets, lower intake gaskets, and all vacuum lines and see if the idle kicks up a bit. If it goes up when you spray it somewhere and the idle climbs a bit, there's yer leak. Also, disconnect your brake booster and apply vacuum to it and see if it holds. If it loses vacuum pressure, your booster is leaking.

[Brody77]

That's kind of the problem. I live in the middle of Western Kansas. The nearest Infiniti dealership/mechanic would be Wichita, KS (about a 3 hour drive) or Kansas City (about a 4 hour drive). But even if there was one near me, I wouldn't want to guess what they would charge to even diagnose it, let alone actually fix it. I called the Wichita dealership to price a new OEM original mass air flow sensor when I was replacing it and they wanted almost $600 (I ended up getting a re-manufactured MAF from AutoZone and even that cost $300) - just for the part only. Meaning had I choose to have the dealership do this relatively simple and straightforward repair, that would have been close to a $1,000 bill with labor right there - just to replace a sensor. On a $4,500 car it would take much at all having an Infiniti dealership working on it before you found yourself upside down in it - possibly VERY upside down.

I definitely agree I probably need to dump it. But in my experience it is very very difficult to sell a car by owner with a lit CEL on. And the few potential buyers who are willing to consider it want to use the lit CEL as an excuse to beat you down on price. I would really like to get this CEL resolved first and then try to sell.

[maxnix]

Did you establish what "transmission service" involved?

You should check your VC by rubbing below them and above the exhaust when the engine is cold. Also, use a hand mirror and your fingers to check if the half moons on the back side are in place.

Then read Paranoid Jack's excellent under plenum knock sensor rehabilitation post.

Did you have an Infiniti Senior Tech performa pre-purchase inspection?

[Brody77]

I'm assuming the transmission service was a standard fluid change, but I don't know. It has one of those service stickers under the hood that simply has "Transmission Service" checked and mileage of 106,532 handwritten next to it on the line. As far as the other recommendations they may be a little above my expertise. I'll definitely read the post, but I didn't quite understand most of what you said.

On a sidenote, I forgot to mention that the airbox is missing 2 of the 4 metal clips that hold the airbox lid down. I've got the two existing clips holding the lid down from opposing corners. Surely this problem couldn't be as simple as non-properly sealed airbox lid, could it? I wouldn't think so since the airbox is pre-MAF and with a brand new MAF installed even if the lid was allowing more oxygen into the intake tube, I would think the new MAF sensor should be able to accurately read that extra O2 coming in and instruct the ECU to properly compensate for it without throwing a trouble code, no?

I also forgot to mention the code was thrown at 74mph and 2650rpm if that makes any difference.

[maxnix]

Some of life's largest problems start with "I assume..."

Have you checked your PCV valves?

How about the EGR valves and the tube in the plenum?

Fuel filter?

[Brody77]

What exactly is the "plenum" and where is it located? Also, where do I find the PVC? I'm definitely going to try the carb cleaner trick to see if I can find a hidden leak, but I would also like to try these other two things.