91Q Low Idle

[timatt]

Got the Q running well following plenum work, however, this morning I noticed that the idle was lower than it was before the plenum work. According to the dashboard tach, I am now running a steady 550 - 600 rpm at warm idle, where it used to steady idle at around 700 - 800 before the plenum work (with at least two bad injectors). This situation is not bad except that there is a very slight vibration in the car at this lower idle speed that is not there at 700 - 800 rpm. Any idea what might be causing the low idle?? Is there an adjustment?

Another thing that I noticed this morning when I got gas is that the fuel tank did not seem pressurized like it normally does when I take off the gas cap. Any thoughts on this one?

timatt

[azskygod]

Just replied to your other post before I saw this one. No backpressure in the fuel system is more indicative of an injector leakdown problem or possibly a pinched o-ring. The idle can be adjusted by turning a screw on the IAC valve, but I would diagnose the other issues before attempting to adjust the idle. Good luck.

AZSKYGOD

[duck3986]

This is the exact symptom I'm facing after finishing a plenum job (replacing knock sensors) on my '98Q. When cold the idle is high enough and smooth, but when warm/hot, the idle drops to 600 rpm and makes the car shake a bit.

I've tried adjusting the screw on the IAC and it makes the idle in neutral a bit higher, but it drops when in gear.

Also, I unplugged the IAC and there was no check engine light and no change in idle. This concerns me that maybe the IAC is not functioning properly.

Anyone have a suggestion on how to check out an IAC?

[Q45tech]

When you did the plenum job did you dissamble IAC and clean it also?Use Consult to test IAC duty cycle ------and manually exercise the solenoid duty cycle.

IAC solenoid/passage is not montored by Obd1 ecu [90-95] it is monitored by seeing the idle speed and the effects.

Adjusting the bypass screw should allow 500-1000 rpm idle in park.

Normally 10% duty cycle in park, 15-20% in drive , 30-35% with AC on.

[elwesso]

With the old Qs (G50) when you unplug the IAC no load, no ac, it only changes the the idle about 50 RPM...

Tim... If you didnt clean the IAC, id suggest doing that... OTherwise, screw in the screw all the way, and pull it out 2.5-3 turns.....

With the gas cap, sometimes mine did that too..

[timatt]

Duck:

Did you remove any injectors when you did your plenum job?

This is exactly my symptom with regard to idle. I'm also having a starting issue (have to have the gas pedal all the way down to start) that I want to address first. Maybe if I clear that up, I will clear up my idle problem also.

timatt

[qship96]

With the old Qs (G50) when you unplug the IAC no load, no ac, it only changes the the idle about 50 RPM...

Tim... If you didnt clean the IAC, id suggest doing that... OTherwise, screw in the screw all the way, and pull it out 2.5-3 turns.....

With the gas cap, sometimes mine did that too..

on my 96q,went to lower the idle,and found IAC screw is covered by wax looking plug-whats up with that?it currently idles at 800-850 warm in park.

[Q45tech]

96Q is different in that you are never supposed to change the IAC bypass screw due to OBD2 emission control [first year bugs]. Just clean everything to return the duty cycle to normal.

Wish the 90-95 were sealed to force owners to clean systems frequently. Hack techs just turned the screws out to quieten customer compliants!

[timatt]

OK: more info. I've got two posts going that I believe may be related so I will post my findings here. The other post relates to my Q being hard to start since the plenum work (new injectors) and I have to press the gas pedal all the way to get it to start.

Tonight I tested fuel pressure. 42 lbs when I turn on the key (not the starter) When I turn off the key, the pressure decays to 0 within about 5 minutes. So now I'm thinking I've got a leaking lower injector O-ring. Is there anything else that would cause this fuel pressure problem?

The car runs well and smooth on the road, but the idle has gotten progressively rougher over the approximately 150 miles I've driven it since the plenum work.

I replaced 5 of the injectors and all of the O-rings when I did the plenum work, so there should be no leaks. Can someone tell me the correct technique for seating the injectors into the fuel rail? i.e. push straight in or twist? I did use silicone lube when I installed them.

thanks,

[DAEDALUS]

The pressure bled down with both the to and from lines pinched off?

[duck3986]

Timatt, I didn't remove my injectors from the fuel rails, but I did have the fuel rails somewhat disassembled.

My car starts up no problem and even idles great in park or neutral. It's just in drive while my foot is on the brake that the idle drops to 600 rpm and is loping.

[timatt]

Daedalus:I didn't try this last night. I can't believe I didn't think of this. I will try tonight.

Is there a way to isolate each fuel rail to determine which rail contains the leaky injector?

Also, I would really like to have someone advise me regarding the correct way to install the injector in the rail; do I push it straight in or do I twist the injector as I push it in. I know to spray it with silicone lube first.

Thanks

[timatt]

I removed the injectors on Friday night and found out that three of the lower O-rings were damaged when I installed them. I replaced the damaged O-rings with new ones and installed them lubricated with sil-glyde. They went in easily, and now the car starts and runs properly and maintains fuel pressure when the engine is off. I learned the following from this experience.

1. Use a heavy grease type lubricant on the injector O-rings. The first time I installed them, I used a spray type silicone lube and the injectors were much harder to push into place. With the sil-glyde silicone grease, the injectors snapped into place quite easily.

2. I don't believe that it makes a difference whether you push the injector straight into its seat or whether you twist while you are pushing the injector in, PROVIDED THAT YOU USE A GREASE TYPE LUBRICANT ON THE O-RINGS.

3. You do not have to remove the plenum completely to acess all injectors. I was able to unbolt the plenum at the runners, remove the EGR connection and a few hoses, then lift the plenum up enough to access the injectors. Using this method, I was able to remove all injectors, replace all O-rings, then re-assemble in 2.5 hours working alone. This might be harder to do if the hoses were not brand new.

4. IMHO, the injector design for at least the early Q sucks and is not as reliable as it should be for a car of this expense and level of sophistication. Nissan should address this at their expense, or at least make the replacement injectors available at a REASONABLE price. Arguments regarding fuel formulation don't hold water in my opinion since I've got other older, much less expensive cars, with a lot more miles,that have more reliable injectors on the same fuel formulations that I'm using in my Q. I do not think it unreasonable for a customer to expect reliability for at least 100,000 miles, particularly when you consider what one of these cars cost when new. I started having injector issues at around 70,000 miles.

[911/Q45]

I'm sure this is a factor in poor sales of new Q45s.

[Jesda]

Nissan fuel system problems have been rather embarassing, going back to the early 80s. Unlike other manufacturers, they didnt plan ahead for crappy North American fuel.

[Q45tech]

Hard for me to be sympathetic when injector failures are so rare in 90-96 Q on conventional gasoline.Same injectors after 14.5 years and 268,000 miles on my 90Q never removed. So rare we don't even stock them in Atlanta. The dealer parts guys act surprised when we order them so does the parts depot in Jacksonville.

We have hundreds of [like aged] Q customers who have never had an injector failure.

[Jesda]

I lived in the northwest for years, and well-populated parts of the midwest and northeast also use reformulated gasline. This is unfortunately something manufacturers had to compensate for in injector and fuel system design. Ford and GM did it, and finally so did Nissan.

If only we could all pump what you guys get down there.

[duck3986]

Timatt,

What about your low idle? I'm still idling at 600 rpm when in gear and stopped, but at 700-750 rpm when in neutral or park.

At 600 rpm the car shakes a bit. I've played with the IAC screw and it hasn't helped.

Don

[timatt]

You wrote:***************************Hard for me to be sympathetic when injector failures are so rare in 90-96 Q on conventional gasoline.Same injectors after 14.5 years and 268,000 miles on my 90Q never removed. So rare we don't even stock them in Atlanta. The dealer parts guys act surprised when we order them so does the parts depot in Jacksonville.

We have hundreds of [like aged] Q customers who have never had an injector failure.***************************

I'm not looking for sympathy here, I'm merely pointing out what I see to be a problem with these cars that the manufacturer does not address.

I acknowledge that gasoline formulations are variable regionally in the US, however it is my opinion that the car should be designed to handle these different formulations for the most part and remain reliable. Not all of us have access to the 'conventional' gas that is apparently available in the southeast.. Here in the midwest, there has been ethanol in gasoline since the 70s. This is nothing new, and Nissan should have known about this and the injectors should have been designed and built to handle this. I have other cars (3 Volvos and a VW) running Bosch injectors (pulsed, not continuous) that have used this fuel for far longer and far more miles than I have on my Q with not a single injector problem.

On this list it is not uncommon to hear of injector problems requiring replacement, so I really don't think that injector failure is rare in these cars. From what I understand, this injector problem is not unique to the Q45 either. The mechanic that I work with stated that he replaces a lot of injectors in Maximas' also; same symptom, rough idle. Evidently the problem is comon enough that the local Nissan dealer here in little ole Fort Wayne stocks injectors for the Q.

I also think that its interesting to note that my car spent its first 67,000 miles in Florida (it was the owner's car for his winter home) before its owner brought it to Indiana last summer where he sold it to me with 67k on it. The car had an intermittent rough idle that I noticed the first weekend I owned it. It would come and go, but gradually got worse until I replaced the injectors two weeks ago at 94k miles. Now it runs perfectly again (finally).

I guess that I just feel that Nissan does not acknowledge the problem and may actually be taking advantage of the situation by charging exorbitant prices for these injectors that in my mind have proven to be less reliable than they should be for a car of this level of sophistication and price. I wouldn't even mind paying the exorbitant price (close to $1200 for a new set plus labor) so much if I had some assurance that the new injectors were going to be more reliable than the originals.

[timatt]

I don't know what to think about the low idle. Even with the new injector seals, the idle is about 50 to 75 rpm ( 600 to 675rpm) lower than it was before I replaced the injectors (around 700rpm). However, now that my new injector seals are no longer leaking, the car idles smoothly even at this lower idle, so I haven't tried to raise the idle.

Are you certain that you have no injector leaks yourself?

[Q45tech]

Not necessarily Ethanols total fault it is the other 37 different formulations that were created after the car was designed tested, then sold.

How does one predict the future?

They all lasted thru the warranty so why is Nissan responsible for something out of their control. You need to blame Clinton EPA which created these formulae.

Nissan doesn't charge $155 per injectors the dealer does - they pay $80 and mark it up to retail.

Don't confuse Japanese Bosch with German Bosch they are two totally different companies with the same name!

I expect to see dozens of failures in January ALONE when Georgia converts To Oxygenated Reformulated Ethanolized gasoline. I'll have to drive 100 miles to fill up to get outside the 50 county area.

Just part of the NEXT $2000 expense in owning an old Q

[duck3986]

I didn't pull the injectors from the fuel rais and I didn't have this low/rough idle prior to pulling the plenum, so I don't think it's a leaky injector.

[Jesda]

Nissan is not legally or financially responsible.

Nissan is, however, putting cars on the road with worse than average injectors. According to consumer surveys, the Q and other Nissans suffer from fuel system problems more often than other vehicles.

It isn't just cows and pickup trucks in the midwest. Some of us own fine automobiles and expecting them to drink ethanol regularly is not unreasonable.

[timatt]

Jesda:

I agree with you.

Nissan may not be legally or technically responsible for the injector problems, however they have developed something of a reputation for putting cars on the road that experience a higher than normal rate of fuel system problems as evidenced by the Consumer Reports findings. I know that in my business (manufacture of disposable medical devices) it is not unusual for us go the extra mile at our expense to keep our customers happy, even when the problem is not our fault. We do this to protect and maintain our reputation as a manufacturer of high quality devices.

If Nissan were to at least address the problem (i.e. provide an improved design for replacement injectors) or at least meet us halfway with regard to pricing, I would feel much better about this issue. And believe me this IS a problem with Nissans. Ignoring this problem is NOT going to help their reputation as a company trying to sell fine automobiles.

Although I love my Q, I'm not sure that I would recommend that a friend purchase one unless they were able to get it for a VERY reasonable price (like I did) that would justify the expensive maintenance costs that are required to keep it reliable. People want reliable cars that require little maintenance. This goal is possible. I've owned such cars in the past.

Just my rant for what its worth. I'm a little testy after the plenum work.

It was nice meeting you and Wes a couple of weeks ago.

[Q45tech]

They did respond they changed the injector design in 1992 for the 1994 model. However the EPA changed the fuel formulations again in 1995 and 1997 and again in 2000................12 states are now suing to drop Ethanol,

California had no Ethanol until recently [this year].

It takes more foreign oil to make Ethanol than it saves when you count the oil uses on the farm and process plant [fuel, fertilizer, electricity, etc] plus ethanol must be transported via truck and rail.

It is the water that Ethanol picks up after production in transport and service station tanks and car fuel tanks that is the future problem

[berniken]

Check Ivory's reply & photo re my I30 IACV inquiry Oct 12. Sounds similar.