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Discussion Starter · #1 · (Edited)
Idle Issues After Head Gasket Replacement

Hello everybody, Happy New Year.

Over the Christmas vacation (I'm a teacher) I replaced the head gasket on my 2004 Nissan Altima 2.5 that has ~140k miles on it. I had a very slow coolant leak, and I saw the water on top of cylinders 2 and 3. I also replaced the thermostat, water control valve, all the plugs, and the serpentine belt while I was at it.

Upon reassembly Monday, she pretty much started right up for me and sounded great. After she was running for a few minutes I noticed a very low, and at times, hesitant idle. It didn't jump up and down drastically, pretty much stayed low (600ish rpm) and seemed to almost stall out at times. I took her out for a spin and she drove great, just when I was stopped the idle was funny and the car was jumpy. When I got back to the house after about a 20 minute drive I went through all the relearn procedures. The idle issue never changed. At one point in the driveway it stalled out. After another test drive the SES light came on with a p0300 random misfire code (the same code I was throwing before the head gasket replacement.) I cleared the code Monday night and figured I'd try all the relearn procedures again Tuesday.

Tuesday morning I drove the car to work, a 30 minute, 30ish mile drive, partially on the highway at highway speeds. Everything was fine again while driving, just the idle issues when stopped at a light or whatnot. When I got to work I disconnected the battery. After work I did the release position and throttle valve relearn procedures, drove home to get it to operating temperature, and then once home did the idle relearn procedure. No change, still idling very low and hesitant and occasionally coming very close to stalling.

This morning it drives me to the doctor in the same state, ok driving, funny stopped idle. Around 5 this evening I went out to do a quick leak check and general poking around. No leaks, all seems good. I started the car to get it up to temp so I can continue leak checking while it's running, went inside for about 10ish minutes to get my sons dinner ready, came outside and the car was not running, stalled out. Fired it up again and noticed now for the first time something different. The idle was holding pretty steady at around 1500rpm. Pumped the gas and it would go to 2500-3000, but not past there. Went for a quick drive and it was all funny, hesitant when I was on the gas, jumpy before it would accelerate, and still not really going above 2500-3000rpm. Sounds like what I've read about limp mode being like.

Lastly, I have not had the SES light come on since I cleared the code Monday, or since I disconnected the battery Tuesday. I have about 70ish miles driven since the battery disconnect and no code.

Can stalling out throw you into limp mode?
How do I get out of limp mode if that's indeed what's going on?
What about my idling issue even before this apparent limp mode situation?
Is there something else I should be checking out, sensors or something?

This forum is the best, thanks a million in advance!!!
 

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Discussion Starter · #2 ·
Update: After doing some reading around the forums, I read that sometimes after stalling the car can go into limp mode and simply leaving it off for a time fixes the problem. Well, I just went out and started up the car and it's not in (what I'm assuming was) limp mode any more. Revved up just fine.

So now I'm just battling that herky jerky idle issue when I'm stopped. Again, its not an idle that's jumping around high and low, it's a very low idle that seems to almost stall every few minutes or so. When the hood is up and I'm watching the engine it shakes back and forth quite a bit when it's doing the almost stall out thing.

Vacuum leak?
Something more major?

Thanks. :)
 

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Could be a vac leak, could also be a MAF issue. Any codes being thrown now? ( PD or "pending" codes do NOT immediately turn on the CEL, however they will show up on a code reader as "P0300 pd")
 

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Discussion Starter · #4 ·
Thanks for your reply 4DRZ.

I'll throw the code reader on the car tonight when I get home. So you're saying that even though my SES light is not on, there might be a 'pending' code that the reader would see?

How might one go about finding a vacuum leak? I've read about stethoscopes...what would I be listening for and where? Just all around the intake manifold?
 

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What's your current issue? High idle or the low unstable idle?

Wish I could offer more advice. Do you own a scan tool, or are you getting the codes checked at AutoZone etc?

Last summer I bought the $149 scan tool from Harbor Freight when I was getting the code for the catalyst efficiency. It's a fairly decent scan tool, and will give real time data. Some things to look at would be MAF and STFT (short term fuel trim). I ended up gutting out the pre-cat and installing an extension on the rear O2.
 

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Discussion Starter · #10 ·
Thanks again Rikoshay.

My current issue is the low unstable idle, close to stalling feeling when stopped/parked. It does not surge high at all. Just once it's all warmed up, she idles really low and sometimes stalls (twice that's happened since Monday).

I have a code reader from Harbor Freight too. It's just the bare bones model. The only time the light has come on since reassembly on Monday was on Monday. It was the p0300 random misfire code. I cleared it Monday night. No codes since Tuesday's battery disconnect, roughly 150 miles since then. I had the limp mode (I assume, no codes) issue after stalling Wednesday in the driveway, but that resolved itself in a few hours.

You mention the precat, you think this could be an exhaust issue I'm having? When I did the head gasket, I opted to not hollow out the precat or buy a header.
 

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I wouldn't think the pre-cat would be plugged if it wasn't having that issue before the head gasket. Typically a plugged cat will result in very low engine vacuum because the exhaust can't go anywhere. Mine was fine, but I gutted it for peace of mind.

The P0300 is a "general missfire" code. If it had a P0301-4 it would indicate which cylinder was misfiring.
 

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Did you know a bout the 2 timing marks on the lower pulley? to mark the correct TDC? did all your timing phase marks line up?

Are all electrical connections on the harness 100%?
Is the ground strap 100% aOK from the battery to frame.?
Do you smell fuel?
Did you put a spacer on the bottom cat O2 sensor?
 

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Discussion Starter · #14 ·
Did you know a bout the 2 timing marks on the lower pulley? to mark the correct TDC? did all your timing phase marks line up?

Are all electrical connections on the harness 100%?
Is the ground strap 100% aOK from the battery to frame.?
Do you smell fuel?
Did you put a spacer on the bottom cat O2 sensor?
Thanks for your reply akashmer.

Yes, I lined the proper mark (3rd mark spaced a little farther away from the other two) on the crank pulley up with the nipple that stuck out and had TDC correctly. When I got the head off pistons 1 and 4 were all the way up and 2 and 3 were down.

I'm 99% certain all the wire harnesses are fully seated, I'll recheck again.

Forgive me for not knowing what the "ground strap" is, can you explain?

I do not smell fuel.

I did not space the second O2 sensor because I did not gut the precat.
 

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its a breathing issue of some kind, or a timing issue like you've suggested. My best guesses would be either a dead or dying MAF, or a crank or cam position sensor on the brink.

There's a slight possibility that the new t-stat could be causing it when it cycles the electric fan on, but I highly doubt this is your problem.

Is the AC running when you have this problem? There's also an even smaller chance that the ac clutch is causing too much load on your engine causing it to die out or rough idle as it cycles as well. Like I said, these last two are reaching, and Im thinking its either a MAF or a CPS.
 

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The Grnd strap is under the battery, when I changed my head all the commotion broke off the connection to the block.....bad place to put a cable. You should check it anyway.
 

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How did you find it?
 

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Discussion Starter · #19 ·
How did you find it?
When I finally got around to checking it (I had a kidney stone shortly after my original post and the past 30 days I've been limited) I took my buddy from work out to listen to the engine and we could totally hear that it was a vacuum leak. After a few mins of poking around we noticed that our fingers placed around where the PCV valve enters the plenum altered the hissing noise. Went home, pulled it off, and sure enough the o-ring was missing. Don't know when or where it went, but I put in a new one and bam, problem solved! I got lucky.

And I have not lost any coolant since the head gasket change, so fingers crossed, it seems my problem has been solved. I was a bit worried because the original head gasket I took off looked fine. I mean, I'm not sure exactly what a "bad" head gasket would look like, especially if it was only slightly compromised, but it looked ok to my untrained eye. I still have to run a compression test, but like I said, I've not been all that up to working on the car in my physical state and in the cold.
 

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When I did mine I made the same observation. I could not find a bad spot either. I believe the rear back passenger side was the culprit. anti freeze slipping under the old gasket the new one had an o-ring like substance on that rear passage way. Its been like 60k miles and everything is fine.

When you had your vacuum leak what did the engine do? did it chug on take off and then work fine? when you let the foot off the gas it stutters?

Aaron
 
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