why is this happening ?
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TECH Enthusiast
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Joined: Feb 2005
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From: new hudson,mi
why is this happening ? ok so after getting my car back from the shop and getting tuned with the cam in my sig and everything else in my sig .when i start my car it wont stay running unless i give it gas and hold it at like 1500 rpm for about 20 seconds then i let off the gas and it will idle , otherwise it will die. well after checking some coonections under the hood while it was running for some reason i disconnected the pcv valve tip the goes to the intake manifold (other end is to the pcv on the valley cover).all of a sudden it idled a lot better. so i turned off my car connected that line back and tried to start car and same thing it just dies. so i disconnected the line again and tried to start it that way. and to my suprise it started right up and went right to idle. why does this happen and why doesnt the car idle when this line is connected as opposed to when it is not connected ? any thoughts and opinions?
thanks guys
thanks guys
Dis you have it tuned with the cam?? If not then thats what you need. It idles when you pull it out because it then lets some unmetered air into the engine, which will allow the rpms to go up. Put the PCV back on and get a tune. With those mods you should know that you need to be tuned, especially with that big cam.
You get excess air to idle on through the PCV and
this tells you the tuner needs to do a better job with
the idle airflow and perhaps the lower end of the VE
table, to dress it for the new pumping characteristics
with the cam. Same effect as drilling the TB, but it's
possible and probably better to do it with the settings.
Doesn't sound like a very thorough / accurate tune job.
this tells you the tuner needs to do a better job with
the idle airflow and perhaps the lower end of the VE
table, to dress it for the new pumping characteristics
with the cam. Same effect as drilling the TB, but it's
possible and probably better to do it with the settings.
Doesn't sound like a very thorough / accurate tune job.
Not to confuse anyone, but I thought it was not possible to use software adjustment to make up idle air for fairly large cams? The hole in the TB and the idle air control valve can only pass so much air. You have to physically open the path (by enlarging the TB hole or opening the throttle blade) in order to pass more air. Am I mistaken?
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Staging Lane
Joined: Jan 2006
Posts: 59
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From: Corpus Christi, TX
I'm not sure, but if I payed a shop for a tune and got the car back in you're shape I would be pretty pissed off. I wouldn't even bother fooling with it, they should have fixed it in their "tune" the first time around. I used to be a mechanic and I would have been damned to let a vehicle leave my bay not running right.
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Originally Posted by BigE
Not to confuse anyone, but I thought it was not possible to use software adjustment to make up idle air for fairly large cams? The hole in the TB and the idle air control valve can only pass so much air. You have to physically open the path (by enlarging the TB hole or opening the throttle blade) in order to pass more air. Am I mistaken?
it is possible, just really hard, which is why people drill so much = easy mode
TECH Enthusiast
Joined: Nov 2004
Posts: 600
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From: Coppell,TX
my understanding of the subject is that the IAC lets in air at an exponential rate based on steps(C^x = y where n is a step, and y is the neccessary amount of air). At a certain point the IAC loses the accuracy to allow the precise amount of neccessary air. Therefore drilling the throttlebody will allow a minimum amount of air to be leaked into the engine, and then the IAC valve can regain its accuracy. (C^x = y - C)