Hard to start when hot

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If you have or can borrow a scangauge or similar tool, you can read what the ECU thinks many of the sensor values are to see if they seem accurate. Intake air temp would be another.

Also you might want to see what Infiniti specific car boards are out there, since this may be a common enough issue that it is common knowledge in that community.
 
A Nissan/Infiniti specific board with good info is http://forums.maxima.org .
The VQ30 has an ambient air temp sensor in the intake tract. It's in the black plastic tubing that enters the bottom of the air filter box. However, according to the FSM, it is for diagnostic purposes only. It is not used for engine operation (which negates part of #4 below).

According to the Haynes Manual, check the following:
1. Air filter clogged
2. Fuel not reaching the injectors.
3. Corroded battery connections, especially ground.
4. Faulty coolant temp sensor or intake air temp sensor.

Seeing as you've all ready replaced the coolant temp sensor, I doubt #4 is the issue. Having had 2 VQ30's, I can say the grounds (#3) are a distinct possibility. Especially on an 11 year old car. The primary engine ground is on the driver's side, front side of the engine block. You can trace your battery's negative cable to find it. It also attaches to the fenderwell below the air filter box. These would be the first 2 I check. The next I'd check is the fuel injector grounds on the intake manifold collector. There are two wires going from the wiring harness that runs along the top of the engine to the aluminum intake manifold. Be careful with these ones, as the bolts are cheap and they thread into aluminum. There are also other grounds on the driver's inner fender and passenger fender beside the coolant recovery tank (2 there). With these grounds, I'd pull each one, clean the area, and snug them back down. These bolts are 10mm, and prone to break if torqued to much. Snug is all it takes.

When I had my '96 Maxima, there was a recall on some emission parts. Something along the lines of an evaporative emission purge control valve or similar. I can't remember the specifics, but the dealership did it for free. I didn't have any driveability issues, so not sure if that would be your problem. But with your symptoms, the emission control system is a possibility.

Hope this helps.

Dave
 
Hi.
The PCV valve, A/T pan gasket, and spark plug tube seal, which were all OEM parts, are replaced on today. I also clean the all the grounds what I know. After that everything is fine except for rough idle. I stared the engine to test overall but as the rpm gauge goes to 1000 when gear is P, I felt the engine is almost dead. It wasn't dead. So I checked under the hood, I can listen to strong vacuum sound. I thought some vacuum hoses were misconnected or missed. I check double it was everthing good. What could this kind of problem make for my car?
Thanks.
 
If you can hear a strong vacuum sound, you may have a vacuum leak. I find it easiest to pinpoint those with a mechanic's stethescope. They're like $2 at Harbor Freight and make it much easier to find such sounds. It's almost amazing how well it works.
 
Oh and a vacuum leak can cause all sorts of issues from idle problems to poor performance and poor economy esp if the vehicle has a MAF.
 
After I checked all hoses and reassembled the parts again, it's gone. I still don't what was wrong.
Anyway. The problem, which was hart to start when hot, is chagned since I replaced some of the parts. The engine even isn't hot but hart to start though. However when it is hot, it's ok. I'm not sure the ratio of the problem like three times of every 10. Does Anyone know about that?
Thanks.
 
Hi.
Finally I'v been a repair shop,where they specialize with only import cars, to check a hard starting problem when the engine is hot. They told several possibilities such as...

1. the error code P1320(ignition signal) even though the car didn't have CEL.
I don't know how did they get the code.
So it might be needed to replace all of the ignition coils -$950.
2. Also the ECU could be malfunctioned. It should go to dealership.
3. The carbon could be accumulated inside the engine.

And they also told me "Inspection only, No guaranty".

After at home, I checked all the ignition coils as the repair manual is written. They are all good. What else I can do to get rid of the code and the problem?
Thanks.
 
Here is the FSM (factory service manual) for your 96 I30. Everything you need to know about your starting trouble is located here. You will need to register to get the download. I did it for my G20 and greatly benefit from the manuals.
 
Sounds like it needs an Italian tune-up. Is it a city car, does it ever get out and breath fresh air?

I've a '97 Maxima SE 5-speed. That manual tranny is good for regular Italian tune-ups.
 
Italian tune-up: a spirited drive to blow the cobwebs out. Needed mostly for carbureted MGs and Alfa Romeos. But you don't have an Italian car, so you need a 'Japanese tune-up.'
 
Right, it's typically running the vehicle at higher rpm than normal; i.e. on a freeway drive run with overdrive off or in one gear down from top gear or something so the rpm's are maybe 4000 or a little more for say 45 minutes or something, that'd be a reasonable italian tuneup
 
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