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Question How to fix high idle with EFI ???

I have been chasing this problem since I went EFI

I'm using a Carrera intake with my EFI and I just can't get idle to drop below 1400 RPM. Worst yet, my idle speed seems to go up when ambient temp is high (>85F) AND engine is warm - it will go up to 1800RPM

I'm not using any idle control and my idle adjustment / butterfly screw is already completely off. I have tried to spray brake cleaner/propane everywhere around the intake, injectors, TB and even the air filter - idle speed doesn't change at all

Changing my fueling/spark timing will only cause AFR to go up & down, but idle speed doesn't change.

I'm out of ideas.... any suggestion what else I can look?

thanks!
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Old 06-15-2007, 06:23 PM
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Throttle cable?
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Old 06-15-2007, 07:05 PM
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on the throttle body theres a plastic thing.looks like a vent,but its not.if you pop that off theres an adjustment for idle.if thats not it then i would say you have a air leak
Old 06-15-2007, 07:52 PM
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See if pinching off your brake booster hose changes the idle speed.

Remove inlet ducting or intercooler and place your hand over the throttlebody while the engine is running. If this drops the idle substantially then adjust the throttle stop set screw so the butterfly closes more, but not to the point of sticking shut.

Check that the large rubber union hose which seals the left and right intake manifolds does not have a cut or split.

My 3.2 throttle body had a forward facing brass hose nipple which was about 8mm dia. Make sure this got plugged.

As dewolf says, make sure there is a little slack in your throttle linkage.

Keep us posted.
Old 06-15-2007, 10:27 PM
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Re: How to fix high idle with EFI ???

Quote:
Originally posted by hobieboy
I have been chasing this problem since I went EFI

I'm using a Carrera intake with my EFI and I just can't get idle to drop below 1400 RPM. Worst yet, my idle speed seems to go up when ambient temp is high (>85F) AND engine is warm - it will go up to 1800RPM

I'm not using any idle control and my idle adjustment / butterfly screw is already completely off. I have tried to spray brake cleaner/propane everywhere around the intake, injectors, TB and even the air filter - idle speed doesn't change at all

Changing my fueling/spark timing will only cause AFR to go up & down, but idle speed doesn't change.

I'm out of ideas.... any suggestion what else I can look?

thanks!
What is your EFI Brain brand??
Old 06-16-2007, 10:32 AM
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What is your timing at idle thru 2000 rpm? I can't believe that reducing your advance doesn't change your idle speed.
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Old 06-16-2007, 03:44 PM
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Sure sounds like an air leak somewhere. Is it that it will only idle at 1400 and no lower or can you just not get it below 1400?
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Old 06-17-2007, 07:48 AM
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When you say you're "not using any idle control," what do you mean? Do you have the stock Carrera TB? Is there an idle air control motor in place? If not, what have you done about the ports that the IAC connect to? It sounds like you have a wide open IAC port between between the top and bottom of the throttle plate. If there's a hose connecting the two, pinch it off.

I was having trouble getting my idle to come down too, even with the throttle plate closed, I was seeing idle speeds of about 1900 RPM. The IAC didn't seem to have the range of flows necessary to control the idle (Carrera manifold, Edelbrock 70 mm TB, Bosch IAC motor, DTA ECU). For some reason, even when the IAC was "off" or "closed" there was still substantial air flow through it. I finally put a manual ball valve in the IAC circuit to cut down the air flow and bring it into range. Eventually, I may remove the valve and replace it with a restrictor.

Rob
Old 06-17-2007, 08:28 AM
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Thanks for all the input guys - I'll see if I can to it later tonight or it will have to be late next week (work travel ).

I think I have plugged all the holes in the TB - the IAC motor is removed and I have capped/plugged the openings. My idle timing is around 10deg and I can't get it to go lower than 1400 no matter what I do. AFR will go lean/rich, and idle and go up from there.

Jim2, "My 3.2 throttle body had a forward facing brass hose nipple which was about 8mm dia. Make sure this got plugged" - I remember there was a metal of some sort (or this was the idle control knob) here. I tightened it all the way in & simply put a decorative plug on top as shown in the pic. Is this the one what you said should be properly plugged?

My butterfly is as close as it gets - the adj screw is not even touching the throttle linkage. I'll test pinching the brake booster hose next and the union.

Will keep you all posted.
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Old 06-17-2007, 12:33 PM
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ok - did a brief diagnostics today. I pinched the brake booster line, no change (in idle speed). I spray propane around the union and the entire TB, no change. Then I remove the air filter and cover the 3" "hole" - the engine dies.

So I'm lost... I can't find the leak Or am I chasing the wrong problem?
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Old 06-17-2007, 06:29 PM
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if the engine died than you know you dont have a air leak.and if the throttle valve is closing all the way i think i know what it is.
Old 06-17-2007, 07:14 PM
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So no leakage from your brake booster, this is good.

Sort of an odd picture angle, but here is the brass fitting which I was questioning. It would be facing forward toward your back seat.


Since the engine died when you covered the throttlebody I would suspect the idle bypass valve or your butterfly plate, though it still could be a combination of a couple leaks.

Put your finger over the oblong port seen inside the throttlebody throat above. This is where the air enters the idle bypass valve which you said you closed by screwing in all the way. Covering this port will confirm the valve is closed if there is no idle speed change.

In the following picture you can see the set screw (yellow paint) which limits the closed position of the butterfly, which you say is backed off. (If so beware that the butterfly will stick shut by binding in the throat of the throttlebody. You will need to readjust it when done) but first try removing your TPS (throttle position sensor) off the end of the throttle shaft to see if it's holding the butterfly open. Don't unplug the tps, just remove it from the shaft. When you installed your tps did you ensure that it had freeplay either direction of the throttle rotation? The butterfly sits at 4 degrees in the throttlebody and has a range of movement of about 86 degrees. TPS sensors have about 120 dregrees of movement to ensure that the throttle motion is within thier range.



Hope this narrows it down for you!

Last edited by Jim2; 06-17-2007 at 07:25 PM..
Old 06-17-2007, 07:20 PM
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Thanks for the suggestion Jim... On the road traveling so won't be able to get to it towards the weekend.

Going from memory - I used that big brass fitting for my MAP reading, so didn't plug that. There are 1 or 2 other smaller ones I believe that I did plug.

Good suggestion on the TPS front - I'll try that. I'm pretty sure there's enough free play there. The ECU reads the "off" position as 25 (in the range of 0-255) but maybe the TPS is putting enough pressure to keep the butterfly open (I need a stronger return spring? )?

I'll keep everyone posted once I get a chance to re-test.
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Old 06-20-2007, 05:15 AM
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In addition to the two long return springs on the Carrera intake on the bell crank and the small spring on the TB, I added another smaller spring inside the small spring on the TB. This helps make sure the TB is closed completely without making the throttle too heavy.
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Old 06-20-2007, 06:39 AM
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I take it you changed your TPS to something other than the factory unit on the 3.2 throttlebody. The issue being that when mounting an aftermarket TPS you need to ensure that the range of motion for the butterfly shaft is centered within the range of motion for the TPS. Otherwies it could result in holding the butterfly open, or limit wide open throttle.
Old 06-20-2007, 04:25 PM
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Here's an update - unfortunately I still have not found the issue

I re-seated the TPS and make sure its not causing tension on the throttle plate. I re-sprayed propane around everywhere I can think of. But nothing...

Now I also have a 2nd strange problem - whenever the car is heat soaked, it will idle waaaayyyyyy lean. I'm talking about going from "normal" AFR of ~14.9 idle to 16.5-17.0! And this condition also causes lean surge until I get to ~2200rpm (slowly).

That kinda makes me think that there's definitely a small leak that magnifies itself as hot air is less dense?
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Old 06-28-2007, 06:11 AM
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you never did tell us if you screwed the idle bypass screw in.its at the back of the throttle valve.it might have a plastic cap over it
Old 06-28-2007, 02:33 PM
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Quote:
Originally posted by rg500930
you never did tell us if you screwed the idle bypass screw in.its at the back of the throttle valve.it might have a plastic cap over it
Hi, oops - my oversight Yes, I did screw it all the way in & put a decorative cover over it too.

Here's a picture that shows that.
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Old 06-28-2007, 04:36 PM
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Have you cut the engine tin bigger to mount the Carrera intake manifold in right? the engine tin from 930 has smaller port.
Have you check on your crank position sensor location with timing gun? turn off close loop. double check with wide band o2 sensor for fuel ratio.
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Old 06-29-2007, 09:18 AM
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Quote:
Originally posted by race911turbo
Have you cut the engine tin bigger to mount the Carrera intake manifold in right? the engine tin from 930 has smaller port.
Have you check on your crank position sensor location with timing gun? turn off close loop. double check with wide band o2 sensor for fuel ratio.
Yes - have cut the engine tin (the engine shroud). Yes - checked my timing against the gun. No - I don't use close loop even though I am using a WBO2.
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Old 06-29-2007, 10:09 AM
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