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High Idle and Vacuum boost

EgonOlsen

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May 4, 2010
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333
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Denmark, Europe.
Finally its warm enough to start on the car again and I have.
(remember when you answer this, im a total noob with no knowledge on cars)

Since it havent really been running for a year or so I fixed what issues I knew about and started her up, just wanted to know if it could start at all. /ubbthreads/images/graemlins/wink.gif

She started right up, ran idle around 2600rpm then slowly climbed to 3000(within 1 min) and stays there, even when the engine is hot it still stay there.
Any ideas what I should be looking at?

My second issue and here my no knowledge shows. /ubbthreads/images/graemlins/wink.gif
The Boost gauge show -20 psi boost(vacuum) whats wrong? did I set it up wrong?
 

GSTwithPSI

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Hey,

High Idle could be caused by anything allowing extra air (usually unmetered) into the motor. This could be caused by a million things. I would start by looking for any obvious vacuum leaks, which are probably the most likely thing to happen to a car sitting over time. I'm assuming this problem didn't exist before you parked it right? Start with looking for simple vacuum leaks (boost leaks are vacuum leaks, just under vacuum instead of boost) and if none exist, we could help you further.

Your boost gauge is reading correctly. It is registering vacuum at idle instead of boost. -20 Hg seems a little low to me for vac reading at idle, as I recall my car pulling almost -30 Hg at idle. -20 could very well be good for you car however (all cars are different and this will depend greatly on you setup), and is by no means a poor reading. On the other hand, it may also point to a vacuum leak or something else going on.

Edit: Your vacuum readings are normal and my car actually runs around -20 as well. Have you or anyone else ever messed with your BIAS/BISS (Base Idle Adjustment/Speed Screw) or have you ever swapped out your TB? A vacuum leak could still be a cause, but such a high idle right from startup, racing up to an even higher idle makes me think otherwise.
 
Last edited:

EgonOlsen

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May 4, 2010
Messages
333
Location
Denmark, Europe.
Ill try to fill a little history in.

I got the car around august last year. and it had been sitting for some time then, but it ran.

It had the IC parts missing.
I put on a new IC(it ran SD and still does) fixed all the bad wiring around the SD setup. New vacuum hoses all around.
The TB have been off the car since the screws where shredded. it got new gaskets on the TB at the same time.

Thats about it, I havent ajusted anything.

I recall my DD galant starts around 2200 cold and go to 800rpm when its hot, I figured the VR4 should do around the same?

More on the car here: click
 
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EgonOlsen

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Messages
333
Location
Denmark, Europe.
I just checked the Biss screw. its all the way down. I took it up just a notch to check and the Idle got even higher.

So thats prolly not it, it cant go lower than it already is.
 

GSTwithPSI

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Quoting EgonOlsen:
I just checked the Biss screw. its all the way down. I took it up just a notch to check and the Idle got even higher.

So thats prolly not it, it cant go lower than it already is.




Did you ground the appropriate connectors to remove the ECU from the equation? I would suggest doing this anyways, even if you BISS is all the way down (which in itself sounds strange to me). Your idle speed should change with the ECU removed from its ability to control idle speed, no matter how the BISS is adjusted.

Also take a look at this: click

If you didn't try this yet, I would go back again and give it a whirl. Hope this helps.
 

EgonOlsen

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May 4, 2010
Messages
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Location
Denmark, Europe.
I tried to find that plug under the hood and I think I did, but it was already unplugged, could that be the issue.

here is a pic so im sure its the right 1.


 

GSTwithPSI

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Ok Man,

The one circled in red is the plug you need to ground.
img.php


Grab it and look at the top. It will look like this:
BISS-07.jpg


As you can see, that is actually like a sorta cap thing on the end of the plug. Remove the cap and you will expose the pins that you need to ground.

Ok, so for the other connector I circled in blue (the 2 pin female connector with the purple center). If my memory serves me correctly this is your BCS (Boost Control Solenoid) connector. I doubt very highly you are using the stock boost control system if your car is modded at all, as this is usually one of the first things to go. Either way, to my knowledge and experience, this won't affect the issues you are having now. This connector is unplugged and lose on my car at home. I would say 90% of the people here are not utilizing this connector, and it's just chillin loose on their cars as well. Someone please chime in and correct me if what I'm saying in regards to this phantom connector is not true...
 

EgonOlsen

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Joined
May 4, 2010
Messages
333
Location
Denmark, Europe.
Aha, ty for clearing that up. this car has way to many plugs that go nowhere. :p

But I found the issue...I think.
There is a little wire on top of the TB, it had broken, I fixed it and the 3k idle is gone, however now another idle problem popped. :p

Now it start at 2000 rpm, but it jumps around 100rpm in a kinda fast manner. 2000-1900-2000 ect. kinda a jump pr second.
when it gets hotter it go slowly down to around 1500rpm and seems to stay there except it still jumps 100rpm every second.
 

GSTwithPSI

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Well sir...you now have an idle surge /ubbthreads/images/graemlins/banghead.gif

Again, there are probably 100 reasons that could possibly cause this. I would still do the BISS adjustment procedure if you didn't already.

After you do that, I would start here with the basics: click and click

After that, do a quick search on here on VR4.org using the words "idle surge". This will give you a lot of ideas on causes, fixes and experiences regarding idle surge, which is a very common problem with these cars (you will see after you search).

If you still need a little more guidance, post whatever progress you have made and what you have done and I, as well as others will surely throw some more suggestions your way.
 
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turbowop

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Yakima, WA
I don't know anybody that pulls 30in/hg at idle. Hell, neither of my cars pull that under full decel. 503 pulls 20 at idle and 1051 pulls 11 due to 272 cams. I'd say his vacuum readings are normal, although his idle rpm is obviously eff'd.
 

GSTwithPSI

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Quoting turbowop:
I don't know anybody that pulls 30in/hg at idle. Hell, neither of my cars pull that under full decel. 503 pulls 20 at idle and 1051 pulls 11 due to 272 cams. I'd say his vacuum readings are normal, although his idle rpm is obviously eff'd.




Upon reexamination of my gauge face, -20 is a much more likely number for my car as well. I was going from memory, as I could best recall my vac at idle. Any other time I'd walk outside to my driveway and confirm this, but being deployed doesn't exactly give me that option. -30 is obviously maxing out the gauge, so you are most definitely right Mark. Thanks for the correction.

images
 

GSTwithPSI

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Quoting turbowop:
For what it's worth, even the FSM states a number somewhere around 18in/hg at sea level for healthy cars.



Yeah, after you mentioned that I googled the specs and 18-22 is about the range that seems to be common...20-25 under decel. Apologies to the OP for the prior bunk info I posted. I believe everything else I said is legit...that is, if Mark says so /ubbthreads/images/graemlins/wink.gif
 

EgonOlsen

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May 4, 2010
Messages
333
Location
Denmark, Europe.
ok plan is to go out later today and adjust the idle thing.

Question 1. will my palmlogger kit ground the terminal in the ODB1 plug?

Question 2. I tried measuring the terminals in the ISC, but its hard to get to it, can I just take it off?

Question 3. I unplugged the ISC then started the car, it made no difference whatsoever, still surged at 1500rpm. why does it not make a difference?
 
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mikus

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Jan 11, 2007
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Location
Aurora IL
did you boost leak test yet? Check your throttle cable, boost leak test, THEN dial in idle. You need to close leaks first.

Boost leak testing will be your first step in addressing many problems on this car.
 

EgonOlsen

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Joined
May 4, 2010
Messages
333
Location
Denmark, Europe.
ok bear with me if I in the following say something completely stupid.


My throttle cable seems fine and slack.

I tried grounding the 2 point under the hood and in the diag plug. No change, I still cant dial in idle cause its still surging.
When the 2 points are grounded it should stop surging right?(the ecu being out of the equation and no longer trying to adjust)
does that mean they aint grounded properly?(defect diagplug or whatever)

if I lightly tap the throttle it goes to 2-3k rpm and stay there for a while, then slowly dropping to 15-1800rpm and start surging again.

Can all this be a ecu issue? not tuned properly for the 850 injectors or similar, or is that just not possible?
 
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