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RPM rise and dive

2K views 13 replies 7 participants last post by  JokerS197 
#1 ·
06 Mustang 5-speed

Just today coming from work I was at a stop , rpm was at normal then it just dove to almost 0 then back to normal then again 4-5 times , it was soooo close to shutting off if I hadn’t given it gas as it fell. As rpms were falling I also felt the car vibrating. I had an 05 before that showed the same symptom so my guess is that it’s one of those common s197 issues ,like the hand brake not working on most. Had to sell my 05 beacause of this issue , don’t wanna sell my 06 ....could it be bad spark plugs, plug wires, fuel filter, injectors, or fuel pump?? I would think it’s a bad IAC or MAF but I’m still new to this style so idk if these have those .
Thanks.
 
#4 ·
Thanks for the replies, not sure of it’s history I just had it for about a week now. It’s at 159k and all I’ve done to it is an oil and filter change....I did notice a small lil pool of fuel on passenger side injector might be a bad o-ring , but I doubt that’s the issue since my previous one did the same thing
 

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#6 ·
Since you don't know the maintenance history of the car, it is possible that the problem could be caused by a maintenance item such as the spark plugs or fuel filter, a dirty MAF sensor, etc. Typically, a problem with one of those parts will be accompanied by a diagnostic trouble code.
Your engine doesn't have a IAC valve to control the idle. The idle speed is controlled by the throttle body on all of the 05-present Mustangs. Your symptoms are consistent with the early signs of a failing throttle body... And maybe a dozen other possible problems that could also be the cause.
Without a code to point you in the right direction, it makes accurately diagnosing the stalling problem more difficult.
You might want to begin doing the general maintenance on the engine. It's possible that you could find the problem during the course of the work. At least you will be able to definitively rule out the inexpensive parts.
 
#8 ·
For a misfire which sounds like what you are describing you want to check fuel- Air- Spark- -Timing- Exhaust- Compression. Otherwise known as fastec acronym. A problem with any of these can cause a misfire/ the engine to stall.

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#9 ·
Surprisingly, I have an opposite problem with my Cobra '99. It drives well but when I stop at the traffic light at idle, RPM jumps to 3000. This does not happen every time but every other time. In order to bring down RPM I engage the first gear and carefully release the clutch at idle. Sometimes it helps to quench it. Nobody knows what it is. Any ideas?
 
#10 ·
Have you checked the idle air control valve? That jumps out the most . It controls allows the engine to control idle by letting air bypass throttle body. Other that this you will want to check the maf and vacuum leaks.

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#12 ·
Today when I drove to work , it didn’t show this symptom, but when I was on my way back home it did it again.(at night it’s cold could
This be a factor?)tomorrow I’m gona change spark plugs,& fuel filter. I have a bad throw out bearing , it chatters at neutral and while driving on 1&2 gear over 3k rpms.........could this issue be it !? A faulty throw out bearing ?
 
#13 ·
I don't think that the throw out bearing is what is causing the idle to fluctuate.
After thinking about it, you should probably fix that leaking fuel injector. If it can leak fuel, then it can also leak air, and that can be a source of a vacuum leak, which can indeed affect the idle.
Also, as a part of the diagnosis process, you should test the charging system to ensure that it is functioning properly, and rule that out as a possible cause.
 
#14 ·
So my 2006 Mustang had experienced something similar. When you come to a stop at a light, you push on the pedal to go and the car starts stuttering like it's going to stall out. Then the car drives like normal. I am not sure if that's the similar situation you're having?

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