What's with the weird "idle" characteristics of my/your cobra anyway

[I_like_turtlez]

Seems like the normal idle RPM is about 950 in closed loop

Have also noticed if you move to neutral while rolling up to a stop the car will hang around 1200rpm until it's been sitting for a couple of seconds with brake pressed

I assume this has something to do with the IAC/PCM parameters & can be adjusted via scan tool(s)

There is a tune on my car(hand held) but reverting back to default doesn't seem to change anything

I've definitely noticed the TPS positions, car barely moves until 90%+ throttle and then it's HANG ON TO YOUR BUTT



Side note: Never buy those Chinesium one-piece headlights from fleabay, horrible build quality & every time I try to adjust one of them the adjuster pops itself off leaving the headlight to flop all over the place.. can't adjust the headlight!

Anyone know where to get quality OEM style 2-piece ones? I want to be able to drive at night again

 

[01yellercobra]

That's normal behavior for the stock idle settings. I think it has to do with emissions and making sure the car doesn't stall from the hydroboost load. A tuner can tweak it.

4V's need RPM. I always stayed above 4k and shifted between 6500 and 7k in my 01 when it was N/A.

 

[I_like_turtlez]

That's normal behavior for the stock idle settings. I think it has to do with emissions and making sure the car doesn't stall from the hydroboost load. A tuner can tweak it.

4V's need RPM. I always stayed above 4k and shifted between 6500 and 7k in my 01 when it was N/A.

Interesting, I didn't notice any vacuum leaks via the ole soapy-water; good to know I'm not crazy.. these things just idle high. The hydroboost makes sense

Yeah they do need RPM to move on demand, I'll be swapping out the 3.27's for some 3.90's if available..

The only problem is these 245's on fresh Nitto's can't even grip a 2nd gear downshift as is(jumps to 4K rpm @ 35mph).. dang near slid my butt into a curb once already! Going to have to be careful with more gearing

 

[Cobra Jet]

Seems like the normal idle RPM is about 950 in closed loop

Have also noticed if you move to neutral while rolling up to a stop the car will hang around 1200rpm until it's been sitting for a couple of seconds with brake pressed

I assume this has something to do with the IAC/PCM parameters & can be adjusted via scan tool(s)

There is a tune on my car(hand held) but reverting back to default doesn't seem to change anything

I've definitely noticed the TPS positions, car barely moves until 90%+ throttle and then it's HANG ON TO YOUR BUTT



Side note: Never buy those Chinesium one-piece headlights from fleabay, horrible build quality & every time I try to adjust one of them the adjuster pops itself off leaving the headlight to flop all over the place.. can't adjust the headlight!

Anyone know where to get quality OEM style 2-piece ones? I want to be able to drive at night again

@I_like_turtlez

Check your PM on here about headlights..

—

I’ve never really experienced any real idle issues with my 94 Cobra. Sometimes a dirty MAF and throttle body will cause slight up/downs with the idle.

Pop the air intake tube off the throttle body and use genuine EFI Throttle Body Cleaner and spray down the butterfly (both sides) and then spray down the throttle body neck too. Do not ever use anything else but EFI throttle body cleaner - don’t use “carb cleaner” or “brake cleaner”, it will damage and strip the protective coating off the interior of the throttle body and blade.

As for the MAF, carefully pull the sensor from the housing and use genuine EFI MAF cleaner, don’t use any other product. Get a Q-tip, saturate the Q-Tip head with the MAF cleaner and gently clean the very very tiny resistor on the bottom of the sensor. Do NOT press onto the resistor, just gently glide over it. Let it dry and then reinstall.

Before starting the car, disconnect the battery, let sit for a good 10-15 mins, then reconnect. Start the car and your idle should be a lot better than it was previously to the above cleanings.

If you haven’t, I would pull your plugs and check their condition. Another thing to check is the spark plug wires, they don’t last forever and even if they “look ok” from the outside of the wire, doesn’t always mean they are.

Spark plug wires don’t last forever and (2) things happen:
- The internal core breaks down over time even if the outer casing is in good shape. When the core becomes degraded, so does spark which affects idle/drivability/power.
- The core wire can become gradually separated from the contact within the boot from when checking plugs.


The whole “set the TPS” sensor is an internet and old magazine myth…. Fiddling with it really doesn’t produce any real world results as much as anyone wants to believe. Sure, you can make the holes oblong and wiggle it and get a different value on your meter reading, but in the grand scheme of things, it’s not going to make one bit of difference to the PCM. As long as it’s within the Ford spec, that’s the only target to be concerned about,

The IAC can be cleaned. Remove it, douse it in EFI TB cleaner (fill it). Cap the holes and shake it vigorously. Empty, repeat and get as much of the carbon cleaned out as possible. If you have a small brush to get in and agitate the carbon, that’s better too. Repeat the douse/empty process a few times, then let it sit and dry… Reinstall and it should be good for another 50k miles.

All the IAC is is a spring loaded piston that gets triggered by the PCM. When the interior of the IAC can gets funked up with carbon deposits, it affects how that piston moves (and if there is enough carbon deposit in it, the piston will be frozen). I’ve done this cleaning process on countless Mustangs and never had an issue cleaning the IAC. Why spend $60-$100+ on a new IAC when the existing can be cleaned for less than $10.

 

[04DeadShort]

I assume you are talking about the 96-98 mod motors? If so, I was told by a tuner years ago it as due to the wasted spark ignition. He didn't explain why and I didn't ask him to elaborate. I guess I should have. lol

 

[I_like_turtlez]

@I_like_turtlez

Check your PM on here about headlights..

—

I’ve never really experienced any real idle issues with my 94 Cobra. Sometimes a dirty MAF and throttle body will cause slight up/downs with the idle.

Pop the air intake tube off the throttle body and use genuine EFI Throttle Body Cleaner and spray down the butterfly (both sides) and then spray down the throttle body neck too. Do not ever use anything else but EFI throttle body cleaner - don’t use “carb cleaner” or “brake cleaner”, it will damage and strip the protective coating off the interior of the throttle body and blade.

As for the MAF, carefully pull the sensor from the housing and use genuine EFI MAF cleaner, don’t use any other product. Get a Q-tip, saturate the Q-Tip head with the MAF cleaner and gently clean the very very tiny resistor on the bottom of the sensor. Do NOT press onto the resistor, just gently glide over it. Let it dry and then reinstall.

Before starting the car, disconnect the battery, let sit for a good 10-15 mins, then reconnect. Start the car and your idle should be a lot better than it was previously to the above cleanings.

If you haven’t, I would pull your plugs and check their condition. Another thing to check is the spark plug wires, they don’t last forever and even if they “look ok” from the outside of the wire, doesn’t always mean they are.

Spark plug wires don’t last forever and (2) things happen:
- The internal core breaks down over time even if the outer casing is in good shape. When the core becomes degraded, so does spark which affects idle/drivability/power.
- The core wire can become gradually separated from the contact within the boot from when checking plugs.


The whole “set the TPS” sensor is an internet and old magazine myth…. Fiddling with it really doesn’t produce any real world results as much as anyone wants to believe. Sure, you can make the holes oblong and wiggle it and get a different value on your meter reading, but in the grand scheme of things, it’s not going to make one bit of difference to the PCM. As long as it’s within the Ford spec, that’s the only target to be concerned about,

The IAC can be cleaned. Remove it, douse it in EFI TB cleaner (fill it). Cap the holes and shake it vigorously. Empty, repeat and get as much of the carbon cleaned out as possible. If you have a small brush to get in and agitate the carbon, that’s better too. Repeat the douse/empty process a few times, then let it sit and dry… Reinstall and it should be good for another 50k miles.

All the IAC is is a spring loaded piston that gets triggered by the PCM. When the interior of the IAC can gets funked up with carbon deposits, it affects how that piston moves (and if there is enough carbon deposit in it, the piston will be frozen). I’ve done this cleaning process on countless Mustangs and never had an issue cleaning the IAC. Why spend $60-$100+ on a new IAC when the existing can be cleaned for less than $10.

Good advice & appreciate you taking the time to type it all out

Always have TB/MAF cleaner on deck; I happened to pull off the CAI the other night & saw the TB was clean(saw Ford's "don't clean this" sticker too) I wanted to check the MAF but it's one of the JLT intakes.. good LAWD they route the thing straight down through the fenderwell just inches off the ground to make sure it sucks up ALL the road water.. I will be changing to a new "in-bay" CAI.. having to remove the wheel liner to access your tube/filter is freakin' stupid too in my opinion

The spark plug wires appear to be fairly new Ford racing blues, the usual upgrade that don't fit in the looms; the car has been driven so little over the last few years I doubt they have any wear to them yet(70,000 mile car) I DO need to pull a spark plug or 2 to check them but I suspect they were changed in the last few years as well.. pulling plugs out of 4.6's is scary stuff..

I like how the TPS operates, makes these cars drive like grocery-getters until you mash that throttle, this car has the most forgiving clutch I've ever seen; don't even need to gas it in 1st honestly

IAC appears to have been replaced very recently, it's spotless & shiny; am aware you can clean them out

Will read PM later today, thanks

 

[I_like_turtlez]

I assume you are talking about the 96-98 mod motors? If so, I was told by a tuner years ago it as due to the wasted spark ignition. He didn't explain why and I didn't ask him to elaborate. I guess I should have. lol

Yes it's a 98, I suspect it has to do with drivable-performance and vacuum(s)

It would seem my car is behaving as it was designed to, the throttle response drive-by-cable is instantaneous but these cars like to take their sweet time dropping back down to idle RPM

Might play around to see if I can find the adjustment; been meaning to look at my fuel trims anyway

 

[CobraBob]

Do you have a factory or aftermarket TB (ie. Accufab)? I know sometimes the TB blades on an Accufab can hang before closing which affects the RPMs at idle. This probably isn't your issue but I wanted to at least toss it out to you.

 

[01yellercobra]

I assume you are talking about the 96-98 mod motors? If so, I was told by a tuner years ago it as due to the wasted spark ignition. He didn't explain why and I didn't ask him to elaborate. I guess I should have. lol

The 99/01's do it in factory form as well. And those have COP ignition. It's in the tune. I was able to tweak my 01 to settle faster.

 

[04DeadShort]

The 99/01's do it in factory form as well. And those have COP ignition. It's in the tune. I was able to tweak my 01 to settle faster.

I'm just quoting was I was told back in the day. My 03 Cobra has a much smoother idle than my 98 does. Both of mine are tuned as well. I will say that both my cars drive fine. The idle has never seemed to affect the car and it idles fine with the AC on so I don't worry with it. But both tunes have been in the car since 2009. I'm sure a lot has come to light since then.

 

[01yellercobra]

I'm just quoting was I was told back in the day. My 03 Cobra has a much smoother idle than my 98 does. Both of mine are tuned as well. I will say that both my cars drive fine. The idle has never seemed to affect the car and it idles fine with the AC on so I don't worry with it. But both tunes have been in the car since 2009. I'm sure a lot has come to light since then.

I wasn't trying to sound like an ass or anything. Just wanted to say what I've learned. One of the first things I did when I started tuning my 01 was getting the idle drop right.

 

[04DeadShort]

I wasn't trying to sound like an ass or anything. Just wanted to say what I've learned. One of the first things I did when I started tuning my 01 was getting the idle drop right.

Nah, I didn't get that impression at all. No worries. But I have been thinking about that conversation the tuner and I had since I read this thread question. I believe I got my 98 tuned in late 2008 then the 03 in 2009. Back then this specific tuner would reach out a few weeks after the car was tuned and asked if there was any issues. I feel like I mentioned how smoother the 03 ran at idle versus the 98. He asked if it was loping and I said no but it has around a 250rpm swing at idle. That was when he mentioned the wasted spark and coil packs. I also remember him saying my 98 bastard fuel system makes it a little more complex as well. He's a great tuner. With the exception of the idle both cars have survived over a decade of aftermarket boost. I have no doubt he could clear it up now. But I plan to swap the Vortech for a turbo and go to a stand alone. I'll worry about it then.