Bad idle when cold

fastazzsupra

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Mar 23, 2006
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I finally finished my never ending rebuild. I've got all but a couple of problems worked out. First, when I start the car in the morning, it idles at 1500rpm. I'll let it warm up for about 5 minutes. When I come to the first stop the vacuum will drop gradually from 18 to 12in/hg. The funny part is, that after I get it to idle long enough to start down the road again it runs and idles perfect. I've got a code 51 fault. The tps, ect , vacuum hoses, and intercooler pipes are new. I was also curious if this could be because I have no egr valve, o2 sensor, cat converter, or charcoal canister? I would appreciate any advice ya'll can give me.
 

gaboonviper85

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Jan 13, 2008
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And why did you remove the charcoal canister, egr, and o2 sensor??!!?!!!!?

I honestly feel like you're too stupid to help if you're wondering why your car runs like shit!

Put that shit back on then come back for assistance! Unless you're running a standalone ecu then indeed you are too far throwed to help!
 

fastazzsupra

New Member
Mar 23, 2006
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Not by my choice. All of the emissions parts were missing when I bought the car. Like I said, I just got the rebuild out of the way. I didn't see how the egr missing would make my engine vacuum drop.
 

InertiaIsBoost

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Dec 29, 2008
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gaboonviper85;1393756 said:
And why did you remove the charcoal canister, egr, and o2 sensor??!!?!!!!?

I honestly feel like you're too stupid to help if you're wondering why your car runs like shit!

Put that shit back on then come back for assistance! Unless you're running a standalone ecu then indeed you are too far throwed to help!
poor babe, take it easy on fast azz supra, he just need some love. Its gets too harsh when your yelling at a man. Yea emission will need to put back on to run properly.
 

jdub

Official SM Expert: Motor Oil, Lubricants & Fil
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Feb 10, 2006
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It won't, unless the block off plates for the EGR ports are leaking ;)

If you re-built it, why didn't you reinstall the EGR and O2? You really do need both.
If the fuel vent line from the tank is just hanging in the engine bay (not plugged), you are asking for a BBQ...the charcoal canister contains the check valve that is used to maintain postive tank pressure...you need it too.

With a code 51, the ECU will not go into idle speed control...you need to fix it.
 

fastazzsupra

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Mar 23, 2006
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That was not my choice in the first place. I'm in the process of getting those parts to put them back on. The previous owner removed them. Anways, how would the egr valve drop my vacuum when cold? I checked the plugs for gas saturating and the were fine. So I pretty sure the o2 sensor missing isn't the cause either. Any thing else that I over looked?
 

gaboonviper85

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Jan 13, 2008
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The vacume is something else...probably stuck throttle plate or iscv not set correctly. Vacume can also be contributed to rpm and fueling which the missing o2 will effect....check the forsale threads and buy an egr as well as all that other crap you're missing as it's all important and effect the motor in very negitive ways when removed unless you have a remapped ecu!

Just so you know...there are ZERO horsepower gains by removing this stuff....at all....but it will indeed help blow your motor without it!
 

jdub

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What do you call "perfect idle"?

You model TB has an air bypass screw on it...the one that is suppose to be full closed from the factory. Wouldn't surprise me if the PO screwed it out to "improve idle" vs fixing it the right way.
 

gaboonviper85

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fastazzsupra;1393798 said:
I have everything except the modulating valve. Exhaust shop told me that the bend is too tight for O2 bung. How far back does the bung need to be welded?

Your exhaust shop is stupid..

2-4" from the turbo

so I take it you're running an aftermarket downpipe?
 

Halsupramk3

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Apr 4, 2005
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there is a fuel pressure up VSV on the back of the intake manifold. it is used when you first start up the car. also the cold start injector may be injecting. try disconnecting one then the other when the engine is cold to see if there is a difference. if the egr was removed the fp up vsv may have been tampered with.
 

jdub

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fastazzsupra;1393800 said:
Idle screw is full closed and it idles at 800rpm at normal temp.

Normal idle is 650 RPM. Like I said before this started going off on all sorts of vectors, you need to fix the code 51. Idle will not work correctly with it present...you can't accurately set timing either.

Halsupramk3;1393810 said:
there is a fuel pressure up VSV on the back of the intake manifold. it is used when you first start up the car. also the cold start injector may be injecting. try disconnecting one then the other when the engine is cold to see if there is a difference. if the egr was removed the fp up vsv may have been tampered with.

The hot start FP up VSV is only active when coolant temp is above a certain level (i.e. HOT START)...no effect at all on a cold start. The only possible issue is if the vac line is disconnected allowing an increase in FP at all times. Plus, it's the VSV that is forward on the intake manifold, not the rear. The EGR VSV is the one at the rear of the manifold. Per this diagram:

vacuum_2h.gif


The CSI is only active when when the starter is engaged (it's call a Cold Start Injector for a reason). It has absolutely no effect on idle or warm-up whatsoever. Once the car is started, the CSI shuts off...it is not possible for it to function without STA active at the ECU.

Basically this post is just full of bullshit Hal. You obviously do not know what you are talking about and are leading this guy on a wild goose chase. Do not post in the tech section again unless you are 100% sure of what you say. This is your one and only warning.
 

gaboonviper85

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Jan 13, 2008
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jdub;1393833 said:
Normal idle is 650 RPM. Like I said before this started going off on all sorts of vectors, you need to fix the code 51. Idle will not work correctly with it present...you can't accurately set timing either.

The hot start FP up VSV is only active when coolant temp is above a certain level (i.e. HOT START)...no effect at all on a cold start. The only possible issue is if the vac line is disconnected allowing an increase in FP at all times. Plus, it's the VSV that is forward on the intake manifold, not the rear. The EGR VSV is the one at the rear of the manifold. Per this diagram:

vacuum_2h.gif


The CSI is only active when when the starter is engaged (it's call a Cold Start Injector for a reason). It has absolutely no effect on idle or warm-up whatsoever. Once the car is started, the CSI shuts off...it is not possible for it to function without STA active at the ECU.

Basically this post is just full of bullshit Hal. You obviously do not know what you are talking about and are leading this guy on a wild goose chase. Do not post in the tech section again unless you are 100% sure of what you say. This is your one and only warning.

sometimes I wonder why you go so far out your own way to help the unhelpable! Although this forum is awesome thanks to people like you but damn man why waste so much energy?

Maybe I'm just made of pure asshole...I don't know..