2002 4.6 Injection Question

Groundshaker

New Member

Apr 14, 2015

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May 5, 2015

#1

• May 5, 2015

• #1

My 4.6 2002 GT when I let off of the gas pedal, the engine slowly returns to idle. It does this even when I am shifting gears. Is this normal for the injection system to do this? This is my first injected car. I do not know if a larger throttle body has been installed. I know larger injectors were replaced with stock ones to pass Calif smog test. Or could it be a weak throttle return spring (I haven't dared to look yet). When I drive the car normally, it takes time for the engine to lower it's rev's before I shift. Any and all info is appreciated .

 

TeamCaffeineGT

Member

Mar 16, 2009

193

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Springfield, MO

May 6, 2015

#2

• May 6, 2015

• #2

Groundshaker,
If this is an automatic car then the car will regulate the idle for the trans gear needs. If the car has a manual trans, I assume you are referring to a condition that is present after you press in the clutch and take it out of gear. Aside from these obvious and quite frankly silly observations, my bet would be on the IAC valve. These have a bad habit of either dying completely (leaving you with a no idle or very rough idle situation) or sticking (causing a high idle issue). You could also have a MAF problem if the ECM has not been calibrated for the change in the injector size when using the stock MAF, however I ran 24lb injectors with the stock MAF for over a year and never had any problems. If you are running like a 42lb injector with the stock MAF, then you will definately need a tune. The other issue that you might be seeing is a unmetered air condition most likely caused by a broken vaccum hose, or a diconnected vaccum line on the plenum somewhere.

Good Luck with the troubleshooting!

 

wmburns

SN Certified Technician

Aug 14, 2009

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Houston Texas

May 6, 2015

#3

• May 6, 2015

• #3

The post does not state what the motor's RPM's are.

Does the idle change when the car comes to a stop?

Note, a fast idle of 1100-1200 when the car is moving is NORMAL for 1996+ Mustang GT's. The idle should drop once the car comes to a complete stop (slow idle). Again this is how they came from the factory.

If the fast idle is higher than say 1500 RPM when moving, this could indicate a problem. A vacuum leak should be the fist thing on the list.

OBTW, the reason that the idle hangs is because of the hydro boost assisted brakes.

Here's some more information on how to trouble shoot IAC/idle issues.
Troubleshoot IAC idle problems 1996-2004 | Mustang Forums at StangNet

 

Last edited: May 10, 2015

Groundshaker

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Apr 14, 2015

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May 6, 2015

#4

• May 6, 2015

• #4

Thanks Guys. I will take note of the rpm when I shift. It does have power brakes. It has a close ratio ( real low 1-4) 5 speed trans with a very tall over drive (best used at 65 mph plus). I just bought a code reader (check engine light came on) so I will run the reader tomorrow and see what I get for codes.

 

restomod66

Active Member

Apr 15, 2003

136

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San Jose, CA

May 7, 2015

#5

• May 7, 2015

• #5

Assuming the vehicle is in good working condition- These cars suffer from what some people refer to as the "hanging idle problem". It's actually quite normal on a 5 speed car for the rpm's to hang a bit between gears. Ford dialed this in to smooth out the shifts & also to help with emissions. Yours may be excessive & something may be in need of servicing but it's impossible for us to know that without more information or literally driving your car.

 

Groundshaker

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Apr 14, 2015

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May 10, 2015

#6

• May 10, 2015

• #6

I am assuming my situation is normal, I did finally get a "check engine " light. I bought a "Innova 3100 code reader. It says P0174 system too lean (bank 2). Anyone have an idea what that means?

 

wmburns

SN Certified Technician

Aug 14, 2009

5,892

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Houston Texas

May 10, 2015

#7

• May 10, 2015

• #7

The number 1 cause is

vacuum leak.

Focus first on areas that can affect the left side. Such as:

• exhaust leak on the left side exhaust manifold gasket.
• valve cover gasket
• EGR system.
• Fuel injector O-rings on the left side.
• Clogged fuel injectors on the left side.

 

Reactions: huckleberry

Groundshaker

New Member

Apr 14, 2015

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May 11, 2015

#8

• May 11, 2015

• #8

Previous to the "check engine soon" warning, my car started to nose over. Two days previous to that, I had purchased gas at a cheapie gas station. I was wearing my shades and didn't notice that I was low on gas until the warning light came on (wonderful dark mustang instrument cluster). Well I had the fuel filter changed (filled with brown gunk like coffee grounds). Also I was getting a misfire, so I installed Bosch iridium plugs. Well, it didn't nose over anymore but the misfire eventually got worse (making me think I have a partially clogged injector). So I will take it to my mechanic and have him take a look and resolve the problem. Like I said, I am new to the world of fuel injection (I should have bought the 68 coupe with a 289 3 spd stick). Hindsight sucks sometimes. This 2002 GT (pictured on the left) is awesome looking but so much junk under the hood LOL. Thanks for the heads up guys ! Oh valve cover gaskets seem to be great. Exhaust is quiet (until you get to the Borla chrome tips LOL).

 

wmburns

SN Certified Technician

Aug 14, 2009

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Houston Texas

May 11, 2015

#9

• May 11, 2015

• #9

If clogged fuel injectors are suspected and looking for a cheaper fix, consider an injector cleaning/flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new. Cheaper than new.

 

Groundshaker

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Apr 14, 2015

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May 13, 2015

#10

• May 13, 2015

• #10

The Culprit,,,, Multiple Vacuum leaks at the air cleaner system ! My mechanic did the "Smoke Test" and found that the "Airaid" system was thrown on (by the used car dealer). I haven't picked up the car yet because it has Eibach springs (maybe shocks too) and I want it replaced with OEM units. The dang car is a snow plow and speed bumps and some driveways are a hazard (scrapes the under carriage). Once these things are resolved, it should be a fun car to drive .