1998 Q45 MIL P0140

[tfvesquire]

Hi All:

I am getting my newly installed salvage yard engine cleaned up and tuned for maximum efficiency and performance. Did a Seafoam soak thru the brake booster to clean out some carbon, changed the oil to synthetic, replaced the pcv valves, cleaned the TB, MAF, IAC and ran some spray Seafoam thru the EGR ports and did not have any CELs until now. Ran some fuel injector cleaner in the tank and during a 100 mile trip yesterday I got some hesitation and stumbling when lightly pressing the accelerator, then the P0140 code (rear heated O2 sensor, bank 1). Would this sensor dying cause my above symptoms or is something else the culprit. I believe I located the correct sensor, but please confirm its location for me.

Any additional info would be greatly appreciated. Also saw the continuing saga with paranoid jack's engine ticking along with a new member. I feel your pain....

[tfvesquire]

Ok, I replaced the drivers side rear downstream O2 sensor because I was continuing to get sluggish acceleration coupled with idle swings to almost stalling to an eventual P0140 code. Replaced the sensor last night with a plug and play sensor from Walker, not Bosch. The old one lookde really carboned up probably when I purged the intake with TB cleaner and Seafoam treatments.

Started the car last night and let the sensor heat up, but did not have the chance to drive it. Idled fine with no fluctuation in the RPMs. Drove the car this morning 2 miles to the train and low and behold, it started to give me some hesitation and idle fluctuating, not quite to the point of stalling, but WTF? Does the computer have to relearn the air/fuel mixture again after installing this sensor or do I need to "break in" the sensor with a few miles on the highway to get it to read correctly? Could it be a partially clogged FPR (fuel pressure regulator)? I already repalced the fuel filter before the engine swap so I know that only has a couple hundred miles on it.

Any imput on this would be greatly appreciated. I am tired of having the car drive perfectly one minute and then a few miles down the road start to hiccup and run either too lean or too rich to idle down properly and accelerate as it should. After the sensor install, not CELs either and no flash of any dash lights indicating any misfires. Checked all teh intake plumbing for leaks or broken hoses and found nothing.

Thanks all!!

Ted V.

[tfvesquire]

Okay, I've put a few more miles on the car some on the highway as well. Now I am getting a seriously low idle at start up (never had this before O2 sensor change) with some darker smoke out the tailpipe (running rich). Gave it at little gas to clear it out, but still had a low idle (around 500 rpms) all the way to the station. When I parked, the car idled normally. WTF????

Is my MAF going bad? I checked the connector and wiggled the wires with no changes. I tried unplugging the MAF and the car instantly died which is my understanding that it is working properly. I will pull it out and clean the screen and wire filament, but this issue is pissing me off. My car ran fine after the engine swap until I tried to get some carbon out and did a Seafoam purge thru the brake booster and a lot of carbon was blown out the exhaust pipe. Did I somehow dislodge some cap that is now redeposited somewhere causing my idle problems? Do I need to erplace both downstream O2 sensors even though I only got a code for the driver's bank?

Any help would be great since I am not inclined to start replacing unneeded parts to try and solve this. I don't think I have a fouled plug sine it idles fine most of the time. I am still getting some hesitation on light acceleration, but full power at WOT. That would seem to rule out the fuel filter. Don't know about the FPR since it came on the replacement engine.

Look forward to hearing from someone who has experienced this and cured it.

Ted V.

[paranoidjack]

I've had to replace my MAF twice, and repair it once.

They seem a common failure on this car, and the major symptoms I've seen is very bizarre idle issues, which I imagine will trigger a bunch of codes as the engine is running way lean or rich.

I'd grab a $40 MAF off of eBay, I have one on the way right now lol!

jack

[OwnerCS]

Here's link to a preventative maintenance story that I just finished on my Son's 99 Maxima.

Bottom line: New NTK/NGK O2 sensors on a car with over 100,000 miles will:

1) Improve performance (reduced sluggishness/jerking in lower gears on a MT)

2) Improve MPG (we are seeing at least 15% better mileage now)

mileage-improvement-preventative-mainte ... 77211.html

[tfvesquire]

Here's link to a preventative maintenance story that I just finished on my Son's 99 Maxima.

Bottom line: New NTK/NGK O2 sensors on a car with over 100,000 miles will:

1) Improve performance (reduced sluggishness/jerking in lower gears on a MT)

2) Improve MPG (we are seeing at least 15% better mileage now)

mileage-improvement-preventative-mainte ... 77211.html

*********************************************
I installed a Walker brand O2 sensor (just the one) downstream since it was a plug in with no splicing and I have used Walker in the past on other cars. Do you think I am getting the idle and fuel/air mixture issues due to the O2 sensor I installed? Should I go with a set of NGK sensors and replace both downstream sensors?

I will try cleaning the MAF and recleaning the IAC and TB and see if that helps. Any additional info would be greatly appreciated.

Ted

[tfvesquire]

Update:

Since I tried to clean the IAC without removing it since I did not have a replacement gasket on hand, I decided to unscrew the IAC motor/plunger and clean that as well as spray a liberal amount of Deep Creep inside the opening that houses the plunger. On a 1/2 tank I poured in some Lubro Moly injector cleaner. Then, I used some Q-tips and a small rag to clean out the inside chamber and vent hole of carbon. Then I sprayed another healthy dose of DC into the TB. Let it soak for about 15 mins and started it up and gas it some healthy gas to blow it out. Drove the car around the block since it was late and let it idle a few mins. Seemed to idle smooth, but I had my fingers crossed for the next morning's test drive.

Started it up this morning and there was no apparent idle fluctuation. Let it run about 3 mins and proceeded to drive to the car wash. No hesitation in the 2 mile trip, ran it thru and was on my way driving in to work. On the way I had a chance to open it up several times with some good WOT bursts. Did not see anything from the tailpipe in my rearview mirror, but after about 15 mins of driving, I started to get some hesitation and idle swings again and it even stalled once. After much swearing and cussing, I gave it another series of WOT bursts and it ran better, but then hiccupped again two more times. By the time I got close to downtwon Chicago, it seemed to be running smoother and idling fine. Light acceleration had no issues and seemed to have more even power band without the need to floor it to "clear its throat". I guess I will know whether I cleaned everything out or if the idle issue will again rear its annoying head on the drive home.

The only sensor I haven't addressed is the EGR temp sensor located at teh base of the EGR valve. Does anyone know whether that sensor (assuming it is caked with carbon) could be contributing to my issues? The car will definitely run rich versus lean when the idle starts to go ape sh*t sometimes to the point of stalling.

Will update again after I put some more highway miles on the car this weekend.