Idle on cold mornings

Drakeborg · Jan 22, 2008

When I go out to start my car in the cold weather after my car has been setting for awhile it doesn't idle right. It starts with no problem, but after about 1 min to min and a half it acts up. The rpms go up and down in a range of about 400-900. The usually result of this is the car dieing. Once i get it warmed up it is fine. To get it warmed up though I usually keep the rpms around 1000 for about 4-5 min. I could use some help on this one, please let me know what I can do.

It is a '94 GT.

drakesdad · Jan 22, 2008

Does it have any mods......
Have you cleaned your MAF sensor and IAC?

earleys94gt · Jan 22, 2008

Maybe something with the EGR or catalytic convertors(if you have them).

To me, it sunds like something involving the secondary air-injection system.

That is what pumps air through the the EGR during the first few minutes of startup

Like drakesdad said, a list of mods would be helpful.

HISSIN50 · Jan 23, 2008

Another vote for your IAC. There's also a chance that something like your ECT is out of calibration during part of it's range.

The EGR doesnt function till the car is warmed up and it doesnt function ever at idle. The secondary A.I.R. system is separate and has almost no impact on performance ever (hence so many people deleting it).

Good luck.

poboys 94 · Jan 23, 2008

I have the same annoying problem, when the temp is above say 40 degrees my cars idle wont hunt but below that it fluctuates bad for a couple of minutes. I always thought that doing a good tweecer tune would cure that, I just havent been able to afford it yet, subscribing

Rock777 · Jan 23, 2008

Another one here, mine does the exact same thing. I have tried cleaning IAC, adjusting idle screw, TPS, etc.etc., still does it. Just like Poboys, when its cold, it's worse.

I am getting a dyno tune within a month, hoping it will help this problem.

Good Luck!

Methodical · Jan 23, 2008

Rock777 said:
Another one here, mine does the exact same thing. I have tried cleaning IAC, adjusting idle screw, TPS, etc.etc., still does it. Just like Poboys, when its cold, it's worse.

I am getting a dyno tune within a month, hoping it will help this problem.

Good Luck!

Make sure they tune for driveability and not just WOT.

From what I can recall from last winter when mine did that my MAF was lean in a 2 or 3 of the MAF points (idle area). EA suggested to richen those points and the hunting idle at startup went away.

Drakeborg · Jan 23, 2008

I think I will clean the MAF and the IAC and see where that gets me. No codes pop up when I scan it, so I will jsut have to shoot in the dark and see what works.
Thanks for the tips folks, I will get busy with them when I get a chance and I will let ya know

As for mods, I had the motor rebuilt and bored out .30 and a bigger cam put in and I have a chip installed. I have been in college the last few years and so I havent done much with the MAF or the TB or injectors or any of the easy bolt on stuff. My plan is to get a steady job so I can start screwing around and make it one hell of a ride.

DDSTANG94 · Jan 23, 2008

o2 censors??

greenlantern · Jan 23, 2008

I doubt its your maf or IAC. Theres a lot of that going around right now. I think your car is trying to warm the o2 sensors. At start up the computer ignores the o2 sensors till it thinks there warm. If there not, that could affect your idle. If you have long tubes then it just adds to the problem.

Dino Dino Bambino · Jan 24, 2008

greenlantern said:
Theres a lot of that going around right now. I think your car is trying to warm the o2 sensors. At start up the computer ignores the o2 sensors till it thinks there warm. If there not, that could affect your idle. If you have long tubes then it just adds to the problem.

I'm in the same boat and I think you've just hit upon the cause of our problem. It hasn't got worse after I had the long tubes installed but since the engine takes longer to warm up now that the weather's cool, the problem's a lot more noticeable.

Drakeborg · Jan 25, 2008

If it is the O2 sensors that are causing my problem, is there any way to fix that?

greenlantern · Jan 25, 2008

Well if in fact you have long tube headers, you could move them closer to the motor. The O2 sensors need to see about 600 degrees to work properly. Moving the O2 sensors is one option, getting into an exhaust set up that places them closer is another. Short tube headers with H pipe usually keep the O2s hotter. This is a common problem with long tubes.

95CobraMike · Jan 26, 2008

maf baby! i had this problem w my car a while back... and im pretty sure that it was the maf... if not i think u said you are getting a tune, they should be able to get rid of it during the tune

Dino Dino Bambino · Jan 26, 2008

My MAF is squeaky clean and the problem's still there. The engine behaves normally when cold until the gauge crosses the thick white line at the cold end. From there until the gauge needle passes the next white line (low end of NORMAL), the engine bucks and coughs intermittently. Once the gauge needle enters the NORMAL zone it clears up again.
I think the problem is that during this transitional phase from cold to warm, the ECT sensor resistance drops enough to make the engine computer think the engine's warmed up, while the O2 sensors haven't heated up enough to tell the computer to go into closed loop mode. The resulting conflict may be causing the engine to temporarily run lean because when I come to a stop, the engine idle speed also tends to drop as low as 600rpm (normally 800) and it feels like it's going to stall but doesn't.
Does that make any sense or am I just becoming demented in my old age?

Methodical · Jan 28, 2008

greenlantern said:
... I think your car is trying to warm the o2 sensors. At start up the computer ignores the o2 sensors till it thinks there warm. If there not, that could affect your idle.

The computer, at least mine, is set for 120 seconds before it goes to closed loop after startup. Not necessarily when the O2s are warmed. It's a time thing - 120 seconds.

And yes you are correct, the long tube headers places the O2s farther away causing them not to warm up. I've seen this issue explain on the EECtuning.org website.

Drakeborg · Jan 28, 2008

The MAF and IAC are clean. No long tubes either. I do have a chip installed that couldnt be messing with things could it?

95BlueStallion · Jan 28, 2008

Im kinda stumped on mine, cause my code reader still hasnt arrived, so I cant check my CEL that comes on and off. It was almost 50 degrees here in Iowa today, and my car idled perfectly... Lately when its been under 30 degrees, I get the surging idle too... So temp is definitely affecting mine...

Idle on cold mornings

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