Strange idle problem

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desmocruiser

desmocruiser

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I have searched the numerous threads and have made many of the inspections/changes mentioned.
1 new oem plugs,wires, cap, etc
2 Air hose seems okay, has trd sc and no leaks detected
3 CEL code for O2 sensor (replaced) & #6 cyl misfire (replaced #6 injector and intake gaskets)
4 Replaced egr valve
5 inspection of wires across the egr (slight wear on clothy shroud no damage to actual wires detected) secured and no change when wires are moved by hand.
6 Compression and leak down tests are both very good

No change to idle problem.

The vehicle: 1997 TRD SC OME 2 1/2 (Slee 4" on the way) ARB, Warn, 305's etc. 79k

The symptom: A slight 30-50 drop in rpm every few seconds after the truck has been dropped to idle. No other performance issues or irregular occurences.

The only thing that seems to improve the "bump" when idling is to crimp the return fuel line just past the regulator on the fuel rail. It seems to be fuel related. My next step is to change the fuel regulator and test the idle speed sensor.

Are people experiencing any fuel pressure problems with the Supercharger? If so how have they been corrected?

To add all of the work has been done or confirmed by a very reputable Toyota dealer.

Thanks for any guidance.
Although it is my first post, I have read/enjoyed numerous, great stuff.
 
Is the idle "hunting"?

Is this an on-going thing or is it new?

What is the curb idle speed?
 
Yes, it seems to be searching for the spot dropping several rpm from ~650. Almost as if it is searching for fuel or message from the ecu.

When you first stop or drop rpms it seems okay then the bump starts every few seconds.

I have owned the vehicle for several months /3000 miles and it has always been present, just seems worse or my ears are much more in tune to it as of late.
 
Maybe the throttle cable is binding which is not allowing the throttleplate to fully close. If the throttleplate is not fully closed the IAC may try to compensate, resulting in the "hunt".
 
Could be, it certainly shows some wear on the outside.
Wouldn't that also cause problems that would show up elsewhere or possibly just related to the idle?
 
Mostly related to idle speed. Could also affect base ignition timing setting if the TPS sees the throttle off-idle and you are trying to time it (been down that road).

If the blower installer follwed the installation instructions to the letter and did not remove the cables from the throttle body, it is very likely that the throttle cable has a tortional twist in the housing and that twist can cause the cable core to bind in the housing.
I wrote an installation supplement for TRD after the innital kit run but I do not know if they ever incorporated that in subsequent manuals.
 
Great if that is the problem I would be grateful! Not a bad pm item anyway. Do you have part numbers?
Thanks CDan!
 
I don't have the part number for the cable in my head but I do stock it.
 
I think I saw your contact info in the vendor section.
Are you in the office Friday 12/23?
If so I will call asap.
thanks
 
Unfortunately still not smooth!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I have since the last post replaced the fuel reg & tps sensor.
I have the cable to install but I have pressed the throttle mech completely closed and there is no change. So I am starting to rule that out, but will change for pm.

The idle will flucuate between 627 rpm to 602 rpm dropping ~20 rpm every few seconds!!

Totally perplexed as to what to try next?????? I have gone back to the wires over the egr valve, very little if any damage. How minor does the insulation have to be effected to cause a noticable problem? Dealer tested with ohm meter and seems to think they are each consistent. And is there a repair other than replacing the engine wiring harness? I have thrown every part imaginable at it and still no change
 
An odd random # 6 idle or missfire in a lx450 is that the wire harness to the ecu rubs through the dash metal brace and randomley shorts the 6 injector wire , take out the glove box and inspect the harness it can be hard to see .
Just a thought

fj55-100
 
I have taken the glove box out, inspected, there is a split in a yellow wire's insulation going in to the ecu. I would think that combined with the minor split in the wires around the egr could certainly be the cause.

Has anyone gone through the pain of replacing the main engine wiring harness? Does anyone know the estimated time and parts cost involved?

Has anyone else had idle problems assoiated to this and is the only fix to replace the entire harness?

Thanks
 
John,
You may want to download the EWD for your vehicle if you have an LX. If you have a LC then I can e-mail you the Engine Control Section from the EWD.

There is a yellow wire that controls the #4 injector. There is a yellow wire that is in the fuel delivery system. There is a Y-L (Yellow-Black?) wire that controls the #6 injector.

Before you pull the wiring harness, a repair of the cracked wire might save you a lot of time and $$$. If that fixes the problem then you can replace the wiring harness at your leisure.

-B-
 
HI,

Im new to the forum and a new TLC owner however have delt with this problem in my x's LCR! In my opinyon it is a good time to remove and check the Idle Air Control Valve. Its on the trorttle body. A little stepper motor with a rubber plunger on it that it moves in and out of the throttle bypass to control idle speed.

The one that I did didnt need to be replaced. After I priced it out I decided to remove it and mess with it. I found that 12 volts on the proper leads would actuate it. After a proper cleaning and a little tinkering I installed it and it worked like a charm! The motor idled per the book and I didnt have to charge my x for the part. I dont rember what year LCR she had, but I would imagine that they all have the throttle body and company in common. However on my last truck (89 Toyota) I found crudd in the idle valve was the cause of poor idle!

Cheers

_travis
 
Beowulf,

Thanks for the offer of the diagram. It is starting to look more and more like a wiring to one fuel/injectors that could be the problem.
 
And it was the wiring harness! Don't underestimate how even the smallest abrasion can cause a problem. Inspect both the harness around the egr area (especially if you have the trd s/c) and the glove box bracing. Mine was compromised in both locations, ironically to the same wire. Perfectly smooth as it should be after a complete engine wiring harness change.
 
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