2002 I35 having convulsions - can't diagnose

[Geechee]

My 2002 I35 started having problems last week - first thought got some bad gas, occasional stumble. Went to Jax, FL last week and it really started stumbling on way back. Stopped at Independent Garage - they put OBDII and found my bad rear O2 (been on for a year) but that was it. After 3 test drives they came back and said needed transmission - noticed tach was swinging when it stumbled so it had to be trans. slip - Oddly, no burnt smell from fluid and it looks clear... Spent the nite and went to a Nissan Dealer next morning for another opinion. Test drove - no issues. Plugged in to diagnose and no issues other than the P138 rear O2 code - Mechanic said to drive it - probably just bad gas. Coming home (200 mile trip) it really started to cut in and out - felt like engine skipping - coil or injector. Pulled into Infiniti dealer at home (Chas, SC) and left it running and asked for the lead mechanic. He finally came out and went for a drive - it was missing and he felt it was a bad coil - definitely ignition. Took into the shop and hour later said that they couldn't find anything wrong - sometimes this stuff happens - Went out of town this week and left it with them again. They test drove and couldn't find anything wrong - said needed to replace 2 rear o2 sensors for $925 - that way, they could remove that issue and focus on what is really going on - I declined. Been driving it a bit and seems to be intermittent - usually worse when hot and pressing the pedal up a slight incline. Today a friend test drove with me and it SLIP and TCS light kicked on - couldn't get TCS back on with switch. Final ride home this afternoon - once on the Interstate, seemed to lose 4th gear - felt it was stuck in 3rd and when I shifted over to 3rd with shifter, seemed to go into 2nd! I'm not a mechanic and hope that posting here might offer wisdom and shed some light on my car's bad behavior. Thanks in advance and sorry this is so long, Geechee

[DevonD]

Hmm. Thats a tough one. Even if the o2 sensors are bad they wont cause that. And if they are, you can replace both of them yourself for a third of the cost the dealership its quoting you. Its very simple and easy to do.

Im just going to throw a whole bunch of ideas out at you here... So, you have obviously had another tank of gas in it and its not just bad fuel. I have ran out of gas twice in my Maxima and it cuts out harshly as well. So maybe get the fuel pump checked out? That would make the most sense to me...

I dont really know how an automatic could be slipping.. it has no clutch to wear out or anything. I guess that could be the issue though. Another thing to consider is the traction controll system it self. I had a friend who hit a curb and it messed TCS. The car wouldnt accelerate after that and when he did get up to speed it thought it was slipping and stumbled.But in these cars when the slip light goes on does it mean the transmission is slipping or that a wheel or something is slipping? I would think its a wheel . If its not in the fuel system im going to say traction controll is freaking out.. An ABS or speed sensor.. something like that..

But there are lots of guys on here that know way more about this than me ...You will here from them soon. Oh and welcome to Nico!

[allensteiner]

when was the last time you replaced the fuel filter? i just did mine and the one i pulled out was the factory one...didn't have problems but the fuel that poured aout of it looked like thick dyed diesel.

[maxhopper]

When you have a bad O2 sensor, the engine can't accurately monitor the air fuel ratio on the exhaust side, so it goes to a default setting that runs rich. In turn that dumps raw unburt fuel into the exhaust. Fuel in the exhaust will destroy the catalytic converter. Replace the bad O2(s) and have the converter checked. O2's can be bought for $70 or less usually.

As for the transmission issue, it could possibly be a solemoid intermittently sticking.

[Geechee]

Thanks to all for the info. I'm still in disbelief that this car is causing this much trouble - I didn't think that was in their nature.

Where would you recommend ordering O2 sensors? Seem to be over $100 where I look...

Tx, geechee

[maxhopper]

http://www.sparkplugs.com They are a NICO sponsor.

[Geechee]

More info - coming home - really hot day - nearly 100. After 5 minutes, care dropped out of 4th and went to 3rd. Interstate speeds - stayed in 3rd. But, the car didn't stumble and just ran at high rpm. Makes me think that ignition coils are not an issue and everything focuses on transmission or temperature sensors. As maxhopper states, maybe a stuck solenoid?

Not sure what other electronic gizmos could create the same issues - I have ordered a rear o2 sensor to hopefully remove the p0138 code that's been constant but don't think that has anything to do with current problems.

Thanks for any thoughts on diagnosis. - best, Geech