Runs bad when engine is cold

[race_to_live]

in my 91 ss, i did the snorkus mod. now after i took pretty much all the stock intake off(minus the 90* on the turbo) it doesn't run well when the engine is cold at all. it will NOT idle when it is cold, it doesn't rev up like it should when it is cold. it just seems like it is getting toooo much fuel. as soon as the temp comes up to normal the car runs like a dream. could this be the result of a bad coolant temp sensor?

[kimokalihi]

This is only after you removed that stuff? Put it back on.

[kimokalihi]

Years ago, before airboxes were designed as resonant systems, it used to be popular to cut additional holes in the air box to allow more air flow for high rpm. This is no longer a good idea. Modern air boxes can flow much more air than the engine will ever use. Modern engines have throttle bodies or carburetors with throats that are typically about 45mm in diameter, about 16 sq.cm in area. The inlet snorkel to a modern air box will be roughly 300 to 800 sq.cm - much larger than the throttle body or carburetor throat. The idea that the snorkel makes for a significant impediment to air flow into the engine is questionable at best. Drilling holes to let in more air is exactly equivalent to drilling holes in your speaker cabinets to let out more sound. Removing the snorkel from your air box is the exact same thing as removing the port in your speakers, the tube that's carefully engineered to have just the right diameter and length to reinforce the bass on your speakers at low frequencies. By altering your air box in any significant fashion, you're most likely going to cost yourself three to five hp in the mid range, and gain nothing measurable at high rpms.

http://motorcycleinfo.calsci.com/Airboxes.html

[kimokalihi]

A system at resonance is nearly perfect - there are small frictional losses in any system, but at resonance these are the only losses. Imagine pushing a child on a swing - it takes very little energy to keep her going at the natural frequency of the swing, just a little push each swing is enough. The only thing slowing her down is air resistance and a little friction in the chains. So at resonance, air flows through a tuned air box almost without resistance. This is as close as we can get to a superconductor of air.

A modern engine with valve overlap will naturally have a dip in the torque at about a third to a half the red line rpm. If the air box is tuned to have minimum resistance to air flow at this rpm, the dip in the torque curve will be partially filled in by the ease of pulling air into the engine.

So, your air box is most likely designed to add horsepower in the mid-range. The air box will have little or no effect on peak hp.

[Legacy777]

While I do believe intakes play a role in how the engine breaths and the stock intake is pretty good.....I also question how much of the above quoted info applies to turbo charged engines.


In response to the original poster. I would double to check to make sure you do not have a vacuum leak. If you don't I'd try putting the stock intake back on & reset the ECU. If you still have problems I'd look at replacing your coolant temp sensor.

[RJ93SS]

Years ago, before airboxes were designed as resonant systems, it used to be popular to cut additional holes in the air box to allow more air flow for high rpm. This is no longer a good idea. Modern air boxes can flow much more air than the engine will ever use. Modern engines have throttle bodies or carburetors with throats that are typically about 45mm in diameter, about 16 sq.cm in area. The inlet snorkel to a modern air box will be roughly 300 to 800 sq.cm - much larger than the throttle body or carburetor throat. The idea that the snorkel makes for a significant impediment to air flow into the engine is questionable at best. Drilling holes to let in more air is exactly equivalent to drilling holes in your speaker cabinets to let out more sound. Removing the snorkel from your air box is the exact same thing as removing the port in your speakers, the tube that's carefully engineered to have just the right diameter and length to reinforce the bass on your speakers at low frequencies. By altering your air box in any significant fashion, you're most likely going to cost yourself three to five hp in the mid range, and gain nothing measurable at high rpms.

http://motorcycleinfo.calsci.com/Airboxes.html

i definitely disagree with the speaker reference. i'm for long and large intakes with few bends and a cooler air source. our stock systems are full of short radius bends and a maf that sits right after the turbulant airbox, it does however have a cooler air source. i am custom desighning and fabricating an intake right now that i believe will be a lot less restrictive and higher flowing, one day when i dyno my car i will do it with both intakes to see if i have any noticeable gains in power

[skid542]

[snooty upitity British accent] As a degreed Aerospace Engineer with a focus on aerodynamics and boundary layer behavior, I would call several items in the above referenced text into question[/accent]

While the text does make a couple of valid points for very specific naturally aspirate engine loads, I still believe benefits can be had by altering the stock intake tract. I agree that is is pretty good but can be improved by removing the snorkus and resonator or by re-piping the air intake lines.

Anything that can be done to remove resistance on the intake tract will be beneficial on a turbo car. I believe it was either COBB or MRT that did a study on the pressure drop across various sections of the subaru intake tract and found that the snorkus did have a significant drop associated with it. The rest of the system from filter to turbo was pretty good, but gains can still be had.

I'm with Josh, check for vacuum leaks as it's easy to bump a hose while you're messing around in that area. Reset the ECU and see if it happens. I'm much more inclined to believe it something like the coolant temp sensor. Maybe the plug for the Idle Air Control got bumped?


If it were related to your change in the intake system, it would also affect your motor when it's hot.

[race_to_live]

where is the plug for the idle air control?
like i said, when the engine is up to running temp, the engine runs very well through the whole rpm range. it just acts bad when it is cold. i was thinking that the idle air control (which is NOT working) had a major part to do with it.
and as for the intake i made not adding any power gain....it did. im new to the subaru, but not new to cars. i have been driving racecars for almost half of my life, i can tell the difference in a pound of air difference in the tires, so i can feel a power difference. it is not TONS of power, but there is more there.

[skid542]

The IAC is located on the side of the throttle body near the TPS. It has a 3/4" (I think, maybe 1/2") coolant hose running up to it. It's kinda yellowish/whitish and the plug should be pretty visible. I want to say the plug connects from the top but I may be mixing that up with the TPS - they're so close together.

Clear as mud right?

[RJ93SS]

where is the plug for the idle air control?
like i said, when the engine is up to running temp, the engine runs very well through the whole rpm range. it just acts bad when it is cold. i was thinking that the idle air control (which is NOT working) had a major part to do with it.
and as for the intake i made not adding any power gain....it did. im new to the subaru, but not new to cars. i have been driving racecars for almost half of my life, i can tell the difference in a pound of air difference in the tires, so i can feel a power difference. it is not TONS of power, but there is more there.

got pics?

[jefferson]

I know Autospeed did an article on flow restriction in the Subaru intake. They opened up the entrance to the airbox, got rid of the snorkus altogether and put the mrt tube in to replace the resonator. They didn't pick up much of anything on top, but the low and midrange were much better. In my opinion most of that stuff is there just to muffle intake noise to meet gov. regs.

That article is where I got the idea for the 45 degree airbox. For some reason they thought it would be too hard to do. I would like to have seen the results after doing the airbox and getting rid of those 45 degree bends as well as the larger box with the maf away from the walls of the box.

Jeff

[Legacy777]

Here's some pics of some various sensors, including the IAC valve.

edit: I apparently forgot to include the link

www.main.experiencetherave.com/subaru/images/injectors

[subytech]

Years ago, before airboxes were designed as resonant systems, it used to be popular to cut additional holes in the air box to allow more air flow for high rpm. This is no longer a good idea. Modern air boxes can flow much more air than the engine will ever use. Modern engines have throttle bodies or carburetors with throats that are typically about 45mm in diameter, about 16 sq.cm in area. The inlet snorkel to a modern air box will be roughly 300 to 800 sq.cm - much larger than the throttle body or carburetor throat. The idea that the snorkel makes for a significant impediment to air flow into the engine is questionable at best. Drilling holes to let in more air is exactly equivalent to drilling holes in your speaker cabinets to let out more sound. Removing the snorkel from your air box is the exact same thing as removing the port in your speakers, the tube that's carefully engineered to have just the right diameter and length to reinforce the bass on your speakers at low frequencies. By altering your air box in any significant fashion, you're most likely going to cost yourself three to five hp in the mid range, and gain nothing measurable at high rpms.

http://motorcycleinfo.calsci.com/Airboxes.html

The biggest problem I have with this article in reference to your problem isn't anything in the article but rather that it comes from a web site about motorcycles. In todays sport bike wars manufacturers dont worry about intakes as resonant systems they are designed from the factory with as little flow resistance as possible. In fact there is an unspoken war between Suzuki and Kawisaki as to who can build the LOUDEST intake in their sport bikes, just my thoughts on the whole thing. Oh and messing with intake and exhaust flow on a motorcycle can really mess up fueling fast if it isn't tuned correctly.

[race_to_live]

well i found out the problem and im pretty sure i have to be an idiot. the IAC was unpluged. when i went to clean the plug, i moved it with my finger and it just fell off. i remember taking it off for some reason but i never knew that the plug was for the IAC. anywho the car runs damn good now. im really pleased that it is fixed.