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I have a stock 2005 Mustang GT with standard 5 speed transmission and it has developed a rough idle problem which culminates in a progressively louder knocking sound, vibration and loss of power. This only seems to occur after I have driven it for 20 minutes or so then come to a stop and shift to neutral to let it idle. I found that if I punch the accelerated and rev the engine the knocking and vibration stop. This phenomena only occurs when idling. Before this started happening I had a bad Throttle Position Sensor and had a local Ford specialist replace it. Also possibly related is weird behavior with the tachometer. Sometimes at idle the tachometer will read 0 RPM’s when it should be reading 700. The phenomena kind of reminds me of a dieseling effect or bad timing. Any ideas? Thank you in advance!

-Rob
 

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I think you need to use a code reader and find out if any fault codes are stored. AutoZone can do it for free.

Frank
 

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You can probably fix the rough running by removing the throttle body (4 bolts), cleaning it with carb cleaner, and wiping out the accumulated dirt. Then use spray electronic cleaner to clean the MAF. I think the rough idle is caused by the dirty throttle plates sticking or binding, so the computer can't quite keep the idle set right.

The tach reading zero is a problem with the stepper motor for the gauge. There are six of them (one motor per gauge) and on a 2005 at least one or two will eventually go bad. The motors cost about $7 each on Ebay and you can solder them in yourself. There is also a guy on Ebay who will fix it for you if you ship him your cluster.

Bruce
 

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This is what I would do first:
Remove the intake hose off the throttle body. Spray the butterfly and bore with throttle body cleaner while moving and holding the butterfly open. Once it is nice and wet, take a toothbrush and scrub the throttle body bore and the butterfly edges. More spray then more scrubbing. Repeat until spray rinses clean. Then let it dry a bit. You can wedge something to hold the butterfly open, so the manifold can dry too. This will help with start-up. Once dry, reassemble the air hose to the TB and start the car.

If you still have problems after this. I would inspect/replace the sparkplugs.

And you’re tach gauge sounds like the stepper motor. I’m in the process of changing mine now, because the fuel and temp have gone out on my ’05.

Hope this helps.
 

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Problem Resolved?

Hello,

I was wondering if this problem was ever resolved? My 2005 Mustang Gt, has been doing the same thing for about a year now and keeps getting worse. Last night it happened about 30 times within a 2 hour span, and shut down three times at different stop lights. It's very scary and I've already taken it in NUMEROUS times and it's like a mystery. No one can figure out what it is. Please help!

-Crystal
 

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Did you ever fix your problem?

I have a similar problem. I've changed the timing chains, tensioners, guides, camshaft position sensor, cleaned the Throttle Body, changed the oil, and checked for any additional codes. It doesn't happen when I'm at speed but, whenever I go from a start in first gear it makes a loud knocking/rattling sound with loss of power. If I turn it off, then on again, sometimes the problem disappears.
 
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