First let me start by saying I've search and searched, then I searched again. I don't know if I'm not trying the right key words but I couldn't find my exact issue...

....So I just bought a 2008 Enthusiast with 14k on the clock (and it's bone stock) a month ago from a non-nissan dealership. I've been having a weird idle issue once the car has been warmed up. I'll drive to the store or something and shut off my car. Come back maybe 10, 20, 30 minutes later. When I start, the rpm's go up like normal but then instead of settling, they drop down to about 400, then jump up to 1000, then settle around 500 or so. I took it to the Nissan dealer on Monday to have it checked it out and they claim they couldn't replicate the problem and on the service order wrong that they idled my car for 45 min and could not find the problem. I spoke to the service manager over the phone and since he couldn't see the problem all he said was "welcome to the world of fuel injection." (I hate ignorance). So I checked my air filters and they're both practically new. I was going to try to clean the TB and MAFs this weekend but I don't see how they would cause this problem only at startup. Any suggestions?

 

I wanted to add that I don't have any CEL's and I've tried disconnecting the batt. for an hour, and the day after that I tried the Idle Relearn.

 

The Car monitors coolant temperature. Possibly that sensor is failing and telling the ECM the wrong numbers and it sees a cold engine and the oxygen sensor sees the wrong fuel mix. It's a therory, but this is a senerio that I have seen on other makes. If a problem like this happens, sometimes the CEL does'nt register a problem.

 

Hey I have 2008 Nismo 350Z and ever since I bought it new. I had the same problem at hot starts. mine would drop to like 300 rpm but it comes b to normal 750 rpm. It only happens at hot start but I never took it serious since it didn't turn off my engine, came close but never turned off.

 

Is this with the AC on?

 

No AC or any other accessories on. Mine has never stalled out either but since it's under warranty I'd like it fixed cause it doesn't seem normal. This weekend I'm going to clean the MAF's and TB. BTW, I always put premium (93 octane) too.

 

fuel pump, or leak on the intake..........

 

sounds to me you have a vacuum problem. if one of your PCV hoses (positive crankcase ventilation) are clogged then you can have a rough idle, stalling, slow idle speed, oil leaks, or engine sludge. If the PCV valve is leaking instead then you can still have a rough idle, stalling or a high idle speed. Do a vacuum test. I have one described in one of my previous posts.

 

+1, Check and or replace PCV. Its cheap and easy to do. Just becareful not to over torque it. They don't go bad often so it just a starting point.

 

some more possibilities and ways to fix erratic idle:

check mounting bolts at the intake manifold for tightness. since you said you have a completely stock car then that should be fine unless it was tampered with at some point.

like i said before, to check and make sure that all the vacuum lines are connected and in good operating condition. There is one that connects from your intake (a metal looking tube toward the front, under the engine cover)to your passenger side valve cover PCV valve called the crankcase ventilation hose. Another one from your intake duct connecting to the rear of your driver side valve cover called the fresh air inlet hose. There also the PCV breather hose that connects the two valve covers. Check all of those lines and clean them out. Also check the PCV valve (which is the male end that sticks out of the passenger side valve cover that connects to the vacuum hose). You can take it out by using an adjustable wrench and screwing it off. Check the O-ring for damage.

also you can look for a vacuum leak around gaskets with soapy water or listening for a hissing sound when the engine is running.

your air filter could be clogged. check that and see what condition it's in.

you could also have a faulty/fuel pump but i seriously don't think its that.

Other than those things theres the rare occurances of a worn timing chan, worn camshaft lobes, burned or leaking valves.

You can check your coil packs and see if any of them are worn in some way to cause them to not work properly. If it's a leaking head gasket you can find out by a cylinder compression check. If it's none of those then it could be a fuel injection or engine control system malfuntion but unless theres some type of loose connection or something restricting flow them i dont think its that.

im sure it's something very simple and i think you'll figure it out. start with the simple stuff first. let me know how it goes.

 

Thanks for all the input guys. I'm sure it's nothing major either since it only does it on warm starts. Once it settles, the idle is smooth. I'm installing my navi tomorrow so I'll have all my tools in the garage already. I'm thinking I'll disconnect the battery overnight tonight to make sure everything reset's and I'll check everything you guys suggested tomorrow. Thanks again and I'll update you guys when I'm done.

 

Ok, so I was able to check the MAFs and TB and amazingly they were both really clean considering the car is coming up on 15k. I left the battery disconnected overnight and after driving it around a little, then doing the idle relearn, the problem is still there. I checked the hoses for loose clamps and cracks but everything seems to be fine. Any other suggestions? Also, does anybody know any reputable dealers in North Jersey that I could go to?

 

my 08 touring does the same thing. It hasn't really concerned me but I'm curious why it does that

 

I'm thinking it might be software related since it only does it on hot starts. I was stuck in traffic forever yesterday and the whole time the idle was steady. Even when I rev it up, it settles at the correct idle. I'm not too worried since there isn't any CEL, but it annoys the crap outta me

 

im having issues with idle that are similar, so much that im throwing the p0507 code. It started happening after I cleaned my TB yesterday. I drove the car around after i cleaned it to make sure i was solid and i had no issue. Today its hotter than hot and i went on a short drive only to have the SES light come on halfway through the drive home (5 minutes). OBD II says that code, im going to clear it and see if it throws it on a cool morning. I've suspected my PCV is going bad, but ive never heard of it before. Its so loud and it sounds like its venting a ton of air i just dont know whats good and whats bad concerning it.