Cuious as to how some have their vacuum lines routed on their 3.5 motors (in a 4th gen).

I have the IACV Adapter from Stephen Max. I have the tube that comes from the PCV valve going into the back of the adapter. The line that runs to the brake booster (if I'm not mistaken) runs to the nipple at the far left of the IM. The other nipple on the curve of the IM needs to connect in order to have a stable idle. Have others simply plugged this line? or am I missing an extra vacuum line?


Idle is spiratic. Before my tps was very much out of spec which cause a idle to go up and down rhythmically. with my VAFCII hooked up TPS is now set with a .3xv @ idle and 4v @ 100% throttle as per FSM.

I start the car rpms will jump up and down, I'll rev the car up a few times, idle drops to 1.2k steady for a few seconds then will gradually rise to about 2k, then bouncy up and down. Its actions are never consistent.

I'm trying to get all my vacuum lines routed properly and set so I can rule that out of the way. I un plugg the TPS idle shoots to 3K but its stable and solid. I plug it back in, crazy idle comes back. I'm thinking either a bad IACV or bad TPS might be the cause.


any ideas?

 

Why do you have a tube going from the PCV to the IACV?

 

It appeared that was how Stephen Max has it setup on Dubbya car.


but that doesnt seem like it would make sense to be hooked up there. One of the main vacuum lines would make more sense, especially for controlling idle.

 

Turns out there is a big hole in my headers (on the rear where the EGR tube went into) so with that open and puffing out air, I have a feeling that is the source of my bouncy idle. Getting it plugged and will try again and see.

 

All vac lines are ran correctly finally.

EGR hole in the headers has been plugged, but I still have a bouncy Idle.
used a 2nd TPS sensor that is fuctional, set it to spec ( 4v @ 100% throttle) still bouncy idle.

I do see my fuel pressure going up and down. This leads me to suspect a mis-fire or something fuel related that might be causing the bouncy idle.

I could use a fuel filter change so that will get changed to eliminate that. At this point I am going to check all sensors, all cam/crank sensors.

The odd thing that I think might aide the solution of my idle is, when I un plug the TPS sensor idle smoothens out and is steady. a Steady 3K idle but steady none the less. . .

any ideas anyone?

 

did you fix the IACV going from the PCV to upper intake manifold location? if so.. what tps are you using?

 

I rerouted the IACV to a proper vacuum line on the manifold. It helped when I cranked the car and idle was 1.5k and decreasing but I still get the fluctuating idle, it goes up a few hundred then down, up and down.

I resoldered my TPS wiring, incase there was a short of some kind (which there didn’t appear to be any). I am using my 4th gen TPS two plug sensor. I tested with a one plug TPS sensor from a 95. Both sensors adjusted to spec, idle issues still persisted.

Going to re-test my crank and cam sensors. I feels like the rear bank is mis firing or the issue lines with the rear bank. When a unplug the TPS sensor it idles at 3K but smooth as gravy, plus the sensor back in. . . back to square one. I’m hoping when I test my cam/crank sensors that maybe one is not fully in spec. . . I could grab the sensor from my beater and hopefully be done with this problem.

 

i dont have any answers for you man... but are you throwing a code?

 

Mdeezy, have you checked your MAF recently? I'd throw another one on there to see if that is your problem. A bad MAF will cause a fluctuating idle due to erratic timing.

Better yet, unplug your MAF after the car is idling, and see if it will hold steady. With the MAF disconnected, it should fool your ECU into holding the timing at 15* +-1 degree. If the idle holds steady, you have found your problem. If you can, get your hands on a scanner that will show timing. That will aid you in the long run.

 

Thanks for that idea golieKeg, I'll try that out, thankfully I have my beater that I can pretty much pull any parts I need. If the MAF is bad, I already have an extra one.

will post back with my finding.

 

wow, i had similar symptoms like you before and i'm pretty sure it was my tps, but it looks like you've checked and rechecked that. did you calibrate it after it was warm?

 

Have you adjusted the TPS as per the Haynes Manual ??

Take it off the car, by a .3mm and .4mm feeler guage and put the .3 inbetween the set screw at the plate. There should be continuity on the meter between pins 5 and 6. Then take teh .3 out and insert the .4 feeler gauge in and there should be NO continuity.

-matt

 

did you ever find the fix to your problem?? just wondering..

 

if I get continutiy with the .4mm feel guage then, I need to shave .1mm off? or the TPS sensor is on too far?


in the same boat as you brother.

 

No you just loosen up the TPS screws and very lightly turn the tps till you are getting continuity with the .3mm and NONE with the .4mm feeler. Once you acheive this, tighten it up and check again. If you still good then your done

-matt

 

marlon do you have an obd scanner? you can use it to set to spec as well as check for codes, I think at autozone like under $70 last time I heard for a pretty decent one. I was thinking about getting this

 

I dont have an OBD scanner, but i can get the TPS sensor set to spec but when its in spec it doesnt cure the idle problem.

I'm going to check for leaks, my intake is very loud which sounds like a leak so I'm going to try and pin point and places for leaks.

 

your engine ground... Where did you ground the harness too i can almost bet thats your problem.

 

all stock ground locations were used.

curious how a ground could cause a fluxating idle?

 

while searching your i/m for the leak just take it off and re install it and all the hoses around it. maybe get an adapter made to use the 5th gen tb that is not drive by just to see if that fixes your idle problem? I have a spare one or 2. or even your 4th gen tb? check the seal where that bolts to the i/m.