02 mustang gt, under acceleration i get a sssss noise. it is noticeable only under a load. i can maintain my speed and no noise. another issue i have is my idle sometimes is at 1100/1200 rpm. i tap the throttle and it kicks down to 750/800 rpm. like kicking off a choke on a carb engine. Any ideas?
noise under acceleration
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08GT500
5 Year Member
Hi,
Likely a Vacuum leak in your Intake piping between the MAF sensor and the Throttle body, or within lines connected to either.
1) Check the IAC for function, leaks or wear.
2) Verify TB is tight to plenum, no sticking opening/releasing throttle by hand.
3) Check Throttle linkage for binding.
Lube.
4) Inspect and replace any damaged vacuum lines, repair less than optimal connections.
-Possible to replicate leak origin with hood open engine running by snapping the throttle open. Likely an obvious issue you’ll spot quick. Good opportunity to clean your Filter.
Good luck.
-John
Likely a Vacuum leak in your Intake piping between the MAF sensor and the Throttle body, or within lines connected to either.
1) Check the IAC for function, leaks or wear.
2) Verify TB is tight to plenum, no sticking opening/releasing throttle by hand.
3) Check Throttle linkage for binding.
Lube.
4) Inspect and replace any damaged vacuum lines, repair less than optimal connections.
-Possible to replicate leak origin with hood open engine running by snapping the throttle open. Likely an obvious issue you’ll spot quick. Good opportunity to clean your Filter.
Good luck.
-John
wmburns
SN Certified Technician
Just wondering. Was the car moving or stationary at the time? Are you aware that the PCM makes different decisions about idle speeds depending upon IF the car is moving or not? The PCM has two idle speeds with higher if the car is moving. The slow idle will be activated once the car comes to a complete stop.
Further the speed of idle that the PCM selects also depends upon the throttle mode. Closed throttle or part throttle. Soooooooo if the TPS closed throttle signal is unstable this can cause an elevated idle.
Here's more information on how the IAC/idle works and how to trouble shoot.
Troubleshoot IAC idle problems 1996-2004
Troubleshoot IAC idle problems 1996-2004
Back to the basics. Check for blown fuses. Especially fuse F2.2 and F2.8 in the Central Junction Box (CJB 1999-2004 MY). Confirm key on power using a known good ground. 1999-2004 MY fuse panel schedule...
www.stangnet.com
Are you positive that the noise is coming from engine and not from the rear end?
08GT500
5 Year Member
Another thought.. How did the issues present themselves, started & escalated over a time period, or just occurred suddenly one day while driving? Did you notice (1) of the (2) issues occurring before the other, or at the same time? Any DTC’s?
-John
-John
Just wondering. Was the car moving or stationary at the time? Are you aware that the PCM makes different decisions about idle speeds depending upon IF the car is moving or not? The PCM has two idle speeds with higher if the car is moving. The slow idle will be activated once the car comes to a complete stop.
Further the speed of idle that the PCM selects also depends upon the throttle mode. Closed throttle or part throttle. Soooooooo if the TPS closed throttle signal is unstable this can cause an elevated idle.
Here's more information on how the IAC/idle works and how to trouble shoot.
Troubleshoot IAC idle problems 1996-2004
Troubleshoot IAC idle problems 1996-2004
Back to the basics. Check for blown fuses. Especially fuse F2.2 and F2.8 in the Central Junction Box (CJB 1999-2004 MY). Confirm key on power using a known good ground. 1999-2004 MY fuse panel schedule...
Are you positive that the noise is coming from engine and not from the rear end?
sounds like passenger side towards the front.
Just wondering. Was the car moving or stationary at the time? Are you aware that the PCM makes different decisions about idle speeds depending upon IF the car is moving or not? The PCM has two idle speeds with higher if the car is moving. The slow idle will be activated once the car comes to a complete stop.
Further the speed of idle that the PCM selects also depends upon the throttle mode. Closed throttle or part throttle. Soooooooo if the TPS closed throttle signal is unstable this can cause an elevated idle.
Here's more information on how the IAC/idle works and how to trouble shoot.
Troubleshoot IAC idle problems 1996-2004
Troubleshoot IAC idle problems 1996-2004
Back to the basics. Check for blown fuses. Especially fuse F2.2 and F2.8 in the Central Junction Box (CJB 1999-2004 MY). Confirm key on power using a known good ground. 1999-2004 MY fuse panel schedule...
Are you positive that the noise is coming from engine and not from the rear end?
I can not replicate the noise while stationary, it has to have a load on it. I can sit idle and sometimes it revs a little high. I tap the throttle and it settles down. Other times it idles as it should.
I thought I found it but a road test proved me wrong. The car has a after market intake. The pcv from the driver side had a bad connection to the intake tube. I repaired it and thought it was it.
08GT500
5 Year Member
Hi,
A photo or 2 of the motor may be worth posting, more specific’s provided = better responses.Knowing it’s a recent purchase is useful info.
PCV leak needed repair, good it’s done whether it factored in or not.
Some questions/thoughts/info:
1) Was the idle normal, less noisy under acceleration when you purchased the car?
2) Did the CPU ever throw a trouble code?
3) Does the car have Shorty or L.Tube Headers?
4) An open element filter with a Cool Air Intake produces a sustained “Howl” sound when the throttle is opened wide while driving, fairly quiet during normal driving. Is the sound more of a higher pitch hiss, whistle, or more of a drone?
Loosen all the CAI clamps and be sure the pipes are inserted deep into the rubber couplers & retorque the clamps. Ensure the Filter is secured tight. All CAI air connections should be checked at both ends. .
-John
i will try to get some pics when i get home.
50/50 on the idle. Sometimes it stays at 1100/1200. I just kick it down. other times it idles fine. The idle does seem a little more erratic with the ac on. Once it actually almost stalled.
Noise was always there.
No codes, cat back exhaust.
Hard to describe the noise other than a hiss. I can maintain speed and no hiss. Full throttle i can hear it but the exhaust is loud too and takes over.
Car also has all new injectors. Previous owner.
50/50 on the idle. Sometimes it stays at 1100/1200. I just kick it down. other times it idles fine. The idle does seem a little more erratic with the ac on. Once it actually almost stalled.
Noise was always there.
No codes, cat back exhaust.
Hard to describe the noise other than a hiss. I can maintain speed and no hiss. Full throttle i can hear it but the exhaust is loud too and takes over.
Car also has all new injectors. Previous owner.
08GT500
5 Year Member
Hi, Just quickly- the A/C initiation should prompt the Car to raise the Idle slightly to offset the added mechanical load. As suggested, sway your attention to checking function of the IACV, it may also leak, there’s a gasket underneath it.
Thought you already did this(?), if so- you may have missed something. Whether the “hiss” is related or not, the IACV has now shown 2 solid symptoms of abnormal function.
-John
Thought you already did this(?), if so- you may have missed something. Whether the “hiss” is related or not, the IACV has now shown 2 solid symptoms of abnormal function.
-John
08GT500
5 Year Member
Hi, Ok - good, nailed one. Staying one at a time is good or it’ll become overly confusing.
1) IAC replacement took care of the idle issue- excellent.
- If your defrost mode is initiated the A/C System also runs, not just for A/C; specifically as a dehumidifier, and it will cycle the system, on/off.
Do you hear/feel the added load from the A/C compressor cycling, that why you’re fixated there? Best bet, try to catch it in action. 1,001 ways to troubleshoot this, but just try- all fans off, all climate control off, see if you get a repeat.
2) “Hiss” is beginning to sound like a typical CAI open filter sound, if it’s checked, no leaks, Filter is attached firmly, no cracks, no CEL’s, it very possible that’s what you’re hearing. They sound like a vacuum cleaner @ low- mid range under a load until exhaust drowns out the noise.
- How does the rate the motors running condition, any hiccups or flat spots, or seem strong?
I’ll look for your reply.
-John
1) IAC replacement took care of the idle issue- excellent.
- If your defrost mode is initiated the A/C System also runs, not just for A/C; specifically as a dehumidifier, and it will cycle the system, on/off.
Do you hear/feel the added load from the A/C compressor cycling, that why you’re fixated there? Best bet, try to catch it in action. 1,001 ways to troubleshoot this, but just try- all fans off, all climate control off, see if you get a repeat.
2) “Hiss” is beginning to sound like a typical CAI open filter sound, if it’s checked, no leaks, Filter is attached firmly, no cracks, no CEL’s, it very possible that’s what you’re hearing. They sound like a vacuum cleaner @ low- mid range under a load until exhaust drowns out the noise.
- How does the rate the motors running condition, any hiccups or flat spots, or seem strong?
I’ll look for your reply.
-John
The clutch is working as it should. It cycles on for 14-17 seconds and off for 7-10 seconds, just counting in my head and not by a stopwatch. The clutch will cycle when in defrost mode or ac mode.
I was fixated on the compressor because to me it sounded like a ac compressor clutch engaging or disengaging. Every now and then I get this noise under the hood.
The motor runs great now that the iac has been replaced. The hiss noise is there under load. While giving it gas and not under load there is no hiss. The air cleaner is filthy, has to be cleaned and oiled. I did notice a different noise at the air cleaner. With the hood open and giving it gas by the intake, it changes tone at the air cleaner when coming back down to idle. . I recorded it but you cant hear it.
I was fixated on the compressor because to me it sounded like a ac compressor clutch engaging or disengaging. Every now and then I get this noise under the hood.
The motor runs great now that the iac has been replaced. The hiss noise is there under load. While giving it gas and not under load there is no hiss. The air cleaner is filthy, has to be cleaned and oiled. I did notice a different noise at the air cleaner. With the hood open and giving it gas by the intake, it changes tone at the air cleaner when coming back down to idle. . I recorded it but you cant hear it.
08GT500
5 Year Member
Hi, Glad to hear she’s running strong. If the air cleaner is quite dirty, it may cause the engines demand for vacuum to get pulled from an area that may not normally leak, a vacuum line, etc. Similar to a vacuum cleaner with a clogged tip
These air cleaners are also vulnerable to cracks where they slide onto the tube & are clamped, also causing the same annoying “hiss”, more under load during hard acceleration. There’s a few filters out there that actually make noises as described, brand new- out of the box.SR is of these. What system are you running, ?
Any possibility it’s an electric cooling fan that’s making a cycling noise & contributing to the confusion? If you want to rule out the A/C compressor clutch isnt engaging when nof necessity, you could disconnect that electromagnetic power source connector, temporarily, see what occurs.
Good luck!
-John
i cleaned the air filter and oiled it up. this made my idle off again. i drove it for a little while then disconnected the battery and drove it again and the idle is back. i disconnected the ac and the noise is still there. I will try to disconnect the fan and try that. the sound is hard to describe, ac compressor clicking on, a sudden bang, relay or valve shutting hard?
08GT500
5 Year Member
Clicking described sounds more like a blend Door actuator issue, being as random as it is. Are you running even the Fan to circulate air through the Vents?
-John
-John
08GT500
5 Year Member
Is it a noise that actually puts an additional parasitic loss on the Motor, like if you’re running A/C & the Compressor clutch engages &
You feel the load on the Motor, or is it just the Noise, itself?
You feel the load on the Motor, or is it just the Noise, itself?
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