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Did I get a bad tank of gas, or is my fuel pump going out?

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Old 08-10-11, 05:55 PM   #1
jjbenzo
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Default Did I get a bad tank of gas, or is my fuel pump going out?

Not sure what I may have going on so thought I would ask. A few days ago I filled our GS430 up with gas (always have used premium). The car then drove fine while running errands for the first 40 miles. After letting the car sit for 30 minutes or so, I came back out to the car, started it up and attempted to go. As soon as I put it in drive, and then put my foot on the throttle, the car hesitated/stuttered for a few seconds before finally moving forward. This happened to me 3 more times at stop signs thereafter. Again, after coming to a stop and then putting my foot back in on the accelerator, the car would chug/hesitate before going. It only happened 3 more times during this trip. Once the car was moving, I had no problem picking up speed while driving. The car then sat for 3 days before I drove it again. Once again, the hesitation happened, but only once more during this latest trip. I initially thought that maybe I got a bad tank of gas, but what throws me off is that it ran fine the first 40 miles. Does this sound like a fuel pump going bad, bad gas, or something else? I have read in another thread that long(ish) starts may be due to a failing fuel pump. I have noticed over the past 6 months or so that it takes a bit longer for the car to start up, however, nothing too excessive, and I never have to sit their trying and trying.

Thanks for your input!
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Old 08-10-11, 08:47 PM   #2
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It might not be bad gas. Wouldn't bad gas cause your car to run like crap all the time? You could try dumping some Stabil or water remover in your tank and see if that helps or siphon out that gas and fill it up with fresh gas but I highly doubt it.
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Old 08-10-11, 08:56 PM   #3
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It actually is most likely a sensor... a faulty throttle sensor or map sensor can cause issues like you are experiencing...

Might be hard to test if there is no check engine light, but there may be a pending code in the ecu regarding it...
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Old 08-10-11, 09:10 PM   #4
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I would change the air filter if it's dirty or haven't been changed. Then clean the MAF sensor. Search Clean Mass Air Flow Sensor, there are lots of threads about it. If problem still persist, I would check out the TPS sensor with a Lab Scope and find the glitch.
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Old 08-11-11, 07:19 AM   #5
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My GS4 did something similar where it was laboring getting started, sputtering...then about a month later I went on a long trip to TN and it failed on the trip, completely stopped going 75mph, after I'f been driving for about 3 hours straight. Luckily I was near a Lexus dealer in Lexington KY, and I got towed there. Of course it started the next morning when they went to start working on it, but they measured the fuel pressure and it was low. They replaced the fuel pump, fuel filter, fuel pressure regulator, and fuel strainer, basically covered all the bases, but I haven't had a lick of trouble since. I think the pump was weak and basically failed, probably heat related from running at high speed for long period, and then when it cooled off started working again. The fuel pump is under the rear seat, don't have to drop the tank, and if I was at home probably would have installed an aftermarket pump to save some money, the parts alone were around $700 at the dealer.
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Old 08-11-11, 08:25 AM   #6
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Check the fuel filter. I had similar symptoms on my 99 Prelude and it turned out to be the fuel filter.
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Old 08-11-11, 09:16 AM   #7
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Well, this is my wife's car so she drives it most of the time. She said she had no issues yesterday, but then again, I drove it last weekend without her when it started having issues so she has not experienced it first hand. I suppose we will ride it out till this tank is empty, fill it up again with new gas and see what happens. If I continue to have issues, I'll take it to the dealer. I'll probably go ahead and order a fuel pump in advance to have it ready if that is indeed the issues. I had the fuel filter changed last winter, spark plugs were changed then as well. If it happens to be a sensor, I'll let the dealer determine that if it gets to the point where I need to bring it in. Thanks for everyone's thoughts.
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Old 08-11-11, 10:35 AM   #8
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To keep the fuel pump cool and to prevent moisture from building up inside the gas tank, it is wise to keep at least 1/4 - 1/2 full. It will help the fuel pump last longer.
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Old 08-11-11, 12:59 PM   #9
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I dont think its fuel pump. Fuel pump would make your gauge go up/down. My car acted funny like this few wekks ago, never did it again. I thought it was throttle sensor, but never found out.
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Old 01-01-12, 09:05 PM   #10
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clean maf meter that did the trick for me and the tb
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Old 10-25-12, 08:09 PM   #11
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So, a year later and we are having these issues again. I started noticing about a month ago after first starting up the car and backing it out of the garage, and into the street that it is as if the throttle/pedal goes dead for a split second. What I mean is that as soon as if put my foot into the throttle, it is like a dead spot for a moment and does not do anything, before kicking in and going. This has happened a few times while already moving as well. My wife seems to think that the car has more issues when the "normal, snow, power" buttone is switche over to power. I feel as if it may be a bit harsher when shifting as of late in power mode, but not neccessarily the cause of the "no go" feeling when trying to accelerate.
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Old 10-25-12, 09:53 PM   #12
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it could be your electronic throttle. Also is it doing this on mostly cold starts?

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Old 10-25-12, 10:15 PM   #13
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Clean ur throttle and maf sensor
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Old 10-26-12, 08:02 AM   #14
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Quote:
Originally Posted by L3XOTIC View Post
I dont think its fuel pump. Fuel pump would make your gauge go up/down.
what? that doesn't even make sense.


OP, it's probably the MAF or the Throttle Position Sensor. Usually when a MAF is on it's way out, it won't throw a code because it doesn't know it's going bad. Try disconnecting the maf cable and drive the car a bit. If it runs fine, then you connect the MAF again and it stumbles, there's your problem.

If it were your fuel pump going out, you'd have a hard time starting the car sometimes, and it'd shut off all together if you didn't keep your foot in it.

The TPS could also be to blame. These are generally pretty cheap and easy to replace.
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Old 01-03-13, 12:47 PM   #15
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Last weekend I ended up spending some time to clean out the throttle body. I used the same CNC throttle body/air intake cleaner that most use. Everything cleaned up quite nicely. I did order a new mass air flow meter and throttle position sensor from Lexus as well. I installed the mass air flow meter last night (I was amazed at all the build up on the old one) and I have an appointment at my dealer to get the throttle position sensor installed (along with fuel injection cleaning) tomorrow. I'm bringing it in because I stripped one of the two screws that hold it in place on the throttle body. So far with just the throttle body cleaning and new MAF meter, the car seems to be running great. My cars only get full synthetic oil and premium fuel, so it is rare that I run into any major issus. Below are a few pictures of the throttle body and the dirty sensor portion of the MAF meter.

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