idle hangs at 1500 rpm?

JymboSlice

Member
Dec 9, 2008
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Hey, when im at a stop light, stopped, and in neutral my idle hangs at like 1500 rpm for a few seconds. then it idles down to 850 rpm and idles fine.. i replaced the IAC valve, did nothing.. and my car isnt tuned fully. (need dyno tune)

could it be the TPS sensor? and how can i test that?

thanks, jimmy
 
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Have you done anything to the throttle body, from cleaning it with solvents or "throttle body cleaner" to adjusting the linkage?

Are you sure there's no vacuum leaks, including the PCV system?
 
Have you done anything to the throttle body, from cleaning it with solvents or "throttle body cleaner" to adjusting the linkage?

Are you sure there's no vacuum leaks, including the PCV system?

i have an accufab 75mm and yeah, i adjusted all the throttle linkages and everything. the throttle body is spotless and doesnt stay open when im off the throttle and yeah, i think i fixed all of the vaccum leaks. i didnt notice any when i put everything back together.
 
i dont have any vacum leaks either, like cruising along an come to stop it hangs like 1500 for 3 or so seconds then idles down, also when sitting ideling it will rev up an down every few seconds an sumthin like clicks on an off when it revs up, but the biggest thing that bugs me is it hangin at like 1500 for few seconds, any things i should try or clean, thanks
 
i have an accufab 75mm and yeah, i adjusted all the throttle linkages and everything. the throttle body is spotless and doesnt stay open when im off the throttle and yeah, i think i fixed all of the vaccum leaks. i didnt notice any when i put everything back together.

The reason I asked what I did is because very often TBs, OE or aftermarket, come with a thin elastomer seal in the throttle body bore intended to almost completely seal the throttle plate when it's closed. This forces all the idle air control to the PCM via the IAC motor.

If that seal is damaged or removed because someone went into the throttle body with a toothbrush and solvent it's possible that the TB blade is now leaking too much air and the IAC, even when closed, doesn't really have control over idle speed any more.

FWIW, Ford does not recommend cleaning its throttle bodies. In the Ford Service Manual I've got, Sec 303-04B-5 states: "Caution: The throttle body bore and plate have a special coating and cannot be cleaned." This is why...

Ditto for throttle plate adjustments: If the plate closed-position screws were messed with then, again, the plate may be open too far and allowing too much air into the engine, resulting in the same effect.
 
The reason I asked what I did is because very often TBs, OE or aftermarket, come with a thin elastomer seal in the throttle body bore intended to almost completely seal the throttle plate when it's closed. This forces all the idle air control to the PCM via the IAC motor.

If that seal is damaged or removed because someone went into the throttle body with a toothbrush and solvent it's possible that the TB blade is now leaking too much air and the IAC, even when closed, doesn't really have control over idle speed any more.

FWIW, Ford does not recommend cleaning its throttle bodies. In the Ford Service Manual I've got, Sec 303-04B-5 states: "Caution: The throttle body bore and plate have a special coating and cannot be cleaned." This is why...

Ditto for throttle plate adjustments: If the plate closed-position screws were messed with then, again, the plate may be open too far and allowing too much air into the engine, resulting in the same effect.

i dont think i've ever cleaned the TB.. its just spotless haha and i dont think i messed with anything on the TB. ever since i supercharged my car, its been doing that
 
I have this same problem but i dont have a supercharger or the P51. I replace IAC and TPS. Problem still happens. I tried the IAC restrictor plate and it still didn't do anything. Someone please let me know whats going on.
 
Thats just it, i have no idea if a tuner can fix it or not. I'm guessing they can fix it on a dyno? You should check for vacuum leaks or anything like that or even an unplugged sensor. With just the JLT you shouldnt be having this problem, especially since you replaced your TPS and your IAC valve.
 
I already had a supercharger and when I installed a accufab 75mm throttle body I ran into the same problem. Was a PITA for half the summer. I was checking everything. It turned out that the blade in the throttle body was off center letting too much air in. There is two allen wrench bolts on the blade that you can adjust the position of the blade. Take off the throttle body and look thru it with some light behind it. Make sure the gap is the same all around it. I must have tested the voltage on my tps 25 times. Waste of time.good luck
 
I already had a supercharger and when I installed a accufab 75mm throttle body I ran into the same problem. Was a PITA for half the summer. I was checking everything. It turned out that the blade in the throttle body was off center letting too much air in. There is two allen wrench bolts on the blade that you can adjust the position of the blade. Take off the throttle body and look thru it with some light behind it. Make sure the gap is the same all around it. I must have tested the voltage on my tps 25 times. Waste of time.good luck

i have an accufab 75mm too. I'm going to try this, did it end up being the throttle body creating this issue then? and did it go away when you adjusted it? thanks