Which car part do I need?
October 30, 2006 10:41 AM   Subscribe

I'm having car trouble. Someone with a similar car suggested I get a certain car part in order to attempt to fix the problem. Help me remember the name of the car part.

I drive a 1994 Infiniti G20 [with an automatic transmission]. Recently, my car started dying and idling low. When I stop at stoplights, begin to shift from reverse to drive while backing out, and sometimes even right after I start the car, the car just dies. When it is in park, it idles under 1,000, and seems generally "jumpy" whenever I am stopped with it in drive.

A friend of mine has a 1995 Infiniti G20, and the same thing happened to her. She got the name of a car part from her husband, but seemed unclear about exactly what her husband had said. We are pretty sure it's the fuel ______ valve. Google turns up a multitude of parts that can fill that blank, but I was hoping someone might be able to use information about the car problem to help me figure out which one.

Bonus question: I know that Infinitis are made by Nissan, and have been told that my engine is identical to the Nissan Sentra of the same year. However, images in the coordinating Chilton's for the Nissan Sentra do not show my engine. I cannot get my hands on an Infiniti Chilton's [if they are even made], so if anyone knows which Nissan, if any, my car is similar to, I would appreciate that knowledge so that I might even be able to determine the location of the mysterious car part when I figure out what it is.

[I am pretty clueless about cars, so please forgive if I have used incorrect terminology, am missing something obvious, etc.]
posted by starbaby to Travel & Transportation (16 answers total)
That sounds like what my sister's car (different make and model) was doing, and she had to have the distributor replaced.
posted by teg at 11:10 AM on October 30, 2006

It could be a bad EGR valve.
posted by caddis at 11:27 AM on October 30, 2006

I don't own an Infiniti, but I find brand-specific automotive forums can be very helpful with problems like this.
posted by SteveInMaine at 11:38 AM on October 30, 2006

The symptoms you give are so common for any number of things to do with either fuel or spark. The problem may lie with the same part as your friend's car, but it could just as easily be a different one.

Rather than guessing which part to change I'd get it looked at by a professional with all the necessary diagnostic tools to find the source of the problem the first time.
posted by Bearman at 11:58 AM on October 30, 2006

it could be a pcv valve ... BUT ... it could be a lot of other things too ... i'd take it to a mechanic and let him figure it out
posted by pyramid termite at 12:12 PM on October 30, 2006

It could be all those things and others. It sounds like a sensor to the computer. The thermal sensor, screwed in usually close to the thermostat valve attached to the engine block and controls idling, fuel consumption, causing exactly the symptoms you describe. It's easy to install at around $25. depending on AutoZone. Given the age of the vehicle, you're about due one. It'll make your engine run more efficiently also, more than paying for itself.
posted by cjburton at 12:42 PM on October 30, 2006

I have had a mechanic look at it; unfortunately, he's a friend of the family, and his knowledge is somewhat limited to large pickup trucks and school buses painted camouflage. At current, I cannot afford a "real" mechanic, nor can I afford to be without my car. So I am attempting small changes that it might be, because, with the age of my car, I'm about due for a new everything...

Thanks for all of your answers.
posted by starbaby at 12:54 PM on October 30, 2006

I'd start by changing out the fuel filter(s). I'm not sure what the configuration of the Infiniti is, but I'd guess that there's a pre-filter located in the gas tank, and a filter located somewhere under the hood. Gunked up fuel filters could cause the kinds of hesitation and dying that you're describing (imagine a chunk of rust in the tank occasionally blocking the fuel pump pickup, or a collapsed layer of filtering impeding fuel flow under the hood), and should be a fairly cheap and easy fix. Even if that's not the problem, it's good routine maintenance.
posted by saladin at 1:10 PM on October 30, 2006

I am not 100% positive, but I am pretty sure the fuel filter's already been changed. I seem to remember my dad and boyfriend handling that one, and since you're describing it as an easy fix, that's probably something they were able to do. Thank you anyway, though.
posted by starbaby at 1:21 PM on October 30, 2006

looks like there are some G20 factory service manuals here.

also, i'd like to second the "take it to a real mechanic" suggestion. rough idle is a pain in the ass because it can be caused by about a million things and haphazardly trying things by swapping parts in and out can turn out to be very expensive:

"maybe it's the fuel filter?" *ch-ching*
"nope, not the fuel filter. maybe the plugs are dirty?" *ch-ching*
"nope, plugs are fine. maybe it's the EGR valve?" *ch-ching*
"nope, EGR's fine. maybe it's the MAF sensor?" *ch-ching*
"nope, MAF's fine. maybe it's the O2 sensor(s)?" *ch-ching*

... and so on. you need some good diagnostic tools. if a mechanic is too expensive, you might try taking it to a parts store - sometimes they'll have some diagnostic equipment lying around and give you their opinion for free.
posted by sergeant sandwich at 2:14 PM on October 30, 2006

The local technical colleges in my area often have days where you can bring your car in and have it worked on for the cost of the parts. This is a classroom setting where you have several supervised students doing the work. You may want to check and see if there is anything similar in your neck of the woods.

The main drawback is that you might have to wait all day for them to actually get to your car, but if you can do it on a day off, you might end up saving a ton of money.

I've used it a couple of times for small things, and have always been pleased with the result.
posted by quin at 5:12 PM on October 30, 2006

If you're feeling frisky to try something yourself, go down to the auto parts store and grab a can of Seafoam. It's an engine cleaner that has helped idling issues in both of my cars.

If you can identify that PCV valve, remove the opposite end of the hose attached to it. Pour about 1/3 of the can in to a paper cup. Start the engine, and let that hose suck up the Seafoam. Don't do it too fast--it'll stall the engine. Just let it suck a steady stream. When it's gone, shut off the engine, re-connect the hose, and let it sit for 5 minutes. Re-start the engine, take it for a drive around the block... and don't be suprised to see a big cloud of white smoke coming out the tailpipe. That's the carbon and other gunk inside your cylinders burning off.

Then, grab a funnel, and dump the rest of the can in to your fuel tank. That will clean the fuel injectors and other fuel system components. It's not a guaranteed fix, but it did work for me... and the smoke show will make you feel like you did something!
posted by bhayes82 at 5:46 PM on October 30, 2006

If you don't smell anything funny or have an engine light come on from misfiring, or have any strange knocks, and if it can be made to happen due to shifting, then it's probably electronic. It could be any number of sensors or controls, or maybe the safety features of the shifter going out, but a Nissan mechanic would need to get involved first, they are also privy to recalls and troublespots. I would also check the battery connections and make sure they are clean and tight (use baking soda and water to declog), this you can do yourself.
posted by Brian B. at 6:33 PM on October 30, 2006

PCV valve? I doubt it but hey they are cheap, replace it. EGR, that is pricey. Pull the vacuum hose and cap it with a golf tee. Start the engine and see if it is still a problem (best to do this with the engine already warm.) If it didn't get better then it probably is not the EGR valve. Vacuum leaks anywhere can cause this issue. It could just be that you need a tune-up but likely not as computers these days compensate for all the old gremlins. That car does not have a carb does it? If so that is another area to investigate. Sometimes just adjusting the idle takes care of these things, although it generally is covering another problem, but if it makes your car run, who cares? Somehow find a manual and fiddle, or get a pro. Your best bet is to explore the vacuum system. The car is aged, aged vehicles often develop leaks, and vacuum leaks wreak havoc on performance. They can be the devil to find but cheap to repair. That said, with these symptoms I think you have a better than even chance of a bad EGR valve. :(
posted by caddis at 7:12 PM on October 30, 2006

If the Sentra is what I think it is, it has a 1.6 or 2.0L fuel injected SR16/SR20 motor. The idle is controlled by a small Idle Control Valve that bleeds air past the butterfly to control the idle speed. The fuel_____valve doesn't really leap to mind as a specific component on this engine. The Nissan ECU for these was generally a Bosch derivative, and can use flashing lights to display a fault code if the problem is a sensor. Can you identify the engine type in your vehicle?
posted by fullysic at 8:02 PM on October 30, 2006 [1 favorite]

You may be in what's known as "limp home mode", cars with fuel injection need input from a variety of sensors to determine how much fuel to squirt in to get the correct mixture of gas and air. Others have named some of these sensors (MAF or mass air flow, temperature, throttle position sensor, oxygen sensor, etc). If one of these sensors doesn't work, the computer falls back to a default mode that allows the car to run, but not very well. I've seen nissans do this and not have the "check engine" light on. Unfortunately, just because the "fuel ____ valve" fixed your friends car, does not mean it will fix yours. You need to have the error codes checked, but any mechanic that works on modern cars (less than 20 years old) has the scanner. You may be able to rent one, or according to this, you can get an adaptor for a laptop or pda. That link also shows all the error codes.
posted by 445supermag at 8:27 PM on October 30, 2006

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