Idle response seems slow

Silverback

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Zack;

This anomaly developed a few weeks ago and doesn't seem to be related to the engine tick (which has gone away) but the partial loss of compression on #6 is still there.

The problem is that idle speed at start up or any change in throttle setting, hot or cold engine, will only return to the XCal set speed of 900 RPM in two distinct stages, first to about 1300 RPM and then after a second or two settles to tuned idle speed of 900 RPM. This is after coming to a complete stop. If I am coasting, the engine speed will not drop below 1300 RPM.

Engine vacuum is 16-17 inches at idle. Difference between Idle speeds in park or drive is insignificant, less than the width of the needle.

The idle speed was set by the previous tuner years ago, I don't recall if the idle creeped up or was orginally set at 900.

I'v visually checked with flashlite the nest of vacumn lines around the EGR. none are in close proximity to the EGR tube which is still shielded from valve to manifold. I checked the vacumn line from the BOV (or whatever it's called) it's OK

What I have done is:

Removed and cleaned the TB with brake cleaner.
Oiled the blade wind up spring and TB return spring.
Checked to see that blades are not binding and are coming to a complete closed position.
replaced IAC and gasket.
Replaced TB gasket
Resistance checked TPS for full open and closed resistance reading plus observing the change in resistance as throttle is opened and closed, all smooth with consistent return to closed throttle reading.
Removed NOS traction control signal wire from TB output to eliminate loading by the NOS computer - no effect.
Engine vacuum normal 16/17 inches.
Engine RPM at driving speeds seem normal from previous observation

Any advice for me?

Would a defective MAF sensor cause this, I've clean it periodically. This
problem did not develop after a MAF or air filter cleaning but I don't rule it out either.

Thanks,

Pat

The car goes in for head repair in March/April time frame. Since October is car has been dormant except for a weekly start/warm up/drive around the block to keep things soft.
 

4DoorBlackTop

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Will it go back to the 100s after it's warmed if? If so this is normal. Are you saying after putting it in gear it will not go below 1500 rpm for anything?
 

Zack

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Zack;
The problem is that idle speed at start up or any change in throttle setting, hot or cold engine, will not return to the XCal set speed of 800-900 RPM. The engine, after throttle is released decreases in two distinct stages, first to about 1500 RPM and then after a second or two settles to tuned idle speed of 800-900 RPM. This is after coming to a complete stop. If I am coasting, the engine speed will not drop below 1500 RPM.
In the beginning of the paragraph you say the idle never goes back to 800-900, and at the end of the paragraph you say it does. :confused:

What is the vacuum reading first of all, and why do you have your idle so high?
With a blower it should be 700-725 in drive and 825-850 in park.

Even a small vacuum leak will cause a high idle. Do you have any PCV lines routed near or ON the EGR tube?
 

Silverback

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Zack;
I edited my OP for clarity and to address all your questions.

Good call on vacuum checks. Since all vacuum is created by the engine(?) could an EATC or other vacumn operated accessory be at fault?
 

Zack

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If you have 16-17 inches of vacuum at idle, you probably have a leak.

These mod motors always pull 20 inches.

When you let off the gas, the IAC is adjusting to the point where it should command the set idle speed. It realizes there is a problem, then it closes more to get it down further.

If the vacuum leak is bad enough, the IAC will be useless.

If you have any ports capped, check that first. The OEM Ford vacuum fittings are the last to deteriorate, its usually vacuum line that was added in.
 

Silverback

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Thanks Zack;

Project for tomorrow feely-feely check each line.

including the ones in the evap and EATC systems.
 

Zack

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Check the operation of the bypass valve as well.
When they stop working, the rpm's do wierd things.
 

Silverback

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Zack;

That was my first order of business. I pulled the by-pass valve and the plunger moves up when I suck on the vacuum port with a test hose. Blowing in does not produce any air leaks.

Not sure how much it takes to activate the valve. Could it be too weak and thus always partially open?

There's a couple on e-bay , same make and model, used.

Checked all the hoses, could a blown fuel pressure valve cause this? I would expect a CEL with that though.
 

Zack

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Zack;

That was my first order of business. I pulled the by-pass valve and the plunger moves up when I suck on the vacuum port with a test hose. Blowing in does not produce any air leaks.

Not sure how much it takes to activate the valve. Could it be too weak and thus always partially open?

There's a couple on e-bay , same make and model, used.

Checked all the hoses, could a blown fuel pressure valve cause this? I would expect a CEL with that though.
Believe it or not Pat, I dont have any further experience with your problem than what I suggested.

I have had such amazing luck with all 5 Marauders Ive owned. Ive never even had a bad coil pack, or a bad window switch.

Good luck in the search!
 

Silverback

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Zack;

Checked the by pass valve, works good. I plugged the vacuum line to the valve, no change.

Thanks Zack for putting me on the right track, I'll keep the thread posted.

Pat
 

Silverback

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Well, I've checked everything I can find, including suggestions from members of the .NET, Crownvic.com CSVT and local mech's.

So, my thinking is that the low vacuum problem is related to the previously reported ticking and partial loss of compression in the DS head.
 

Zack

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Well, I've checked everything I can find, including suggestions from members of the .NET, Crownvic.com CSVT and local mech's.

So, my thinking is that the low vacuum problem is related to the previously reported ticking and partial loss of compression in the DS head.
Im curious why you chose to take your car elsewhere than me.

You realize you will be paying an astronomical amount more for the same service right?

Im here if you change your mind.
 

Zack

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For example:

If its a cut and dry head removal, head rebuild with new gaskets and seals, my cost with parts and labor would be in the ballpark of 1000-1250.

You cant beat that
 

Silverback

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Im curious why you chose to take your car elsewhere than me.

You realize you will be paying an astronomical amount more for the same service right?

Im here if you change your mind.

If I understood correctly, you were booked up through the winter and into the spring.

I'll consult with Patricia and e-mail you.

Regards,

Pat
 

Zack

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If I understood correctly, you were booked up through the winter and into the spring.

I'll consult with Patricia and e-mail you.

Regards,

Pat
I always have time time to save people money Pat.

I certainly dont want to step on Marty's toe's, but Im cheaper, faster and the most experienced.

Stay in touch. :biggthump
 

musclemerc

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I always have time time to save people money Pat.

I certainly dont want to step on Marty's toe's, but Im cheaper, faster and the most experienced.

Stay in touch. :biggthump
Kinda hard to step on someone's toes when your speaking the truth.
 

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