My car runs like total crap in cold weather, almost as if it is missing or something. In warm weather, (or after the engine has warmed up in cold weather) it runs perfectly normal. What could this be?? I'm assuming a bad sensor, but which one. My O2 was recently replaced. BTW, I have a 91 camaro 305 tbi auto. Thanks.

 

Are you using a 160* t-stat by any chance?

 

YES, I removed the hypertech chip that goes with it cause I thought it was giving me crap. I'm now just running the stat and switch. Could this be?? (removing the chip didn't make things any better or worse)

[This message has been edited by fbodfreek (edited January 22, 2001).]

 

With a 160* T-stat, it makes the engine think it is cold and causes problems in cool weather. At a minimum, it will burn more gas needlessly and possibly run richer @ WOT. A TB bypass just further compounds this.

The Hypertech eprom doesn't do a lot, mostly the temeperature the fans turn on and off, plus a little extra spark advance at mid-rpm range. Possibly raised the speed that the TC locks up a few mph higher. That's about it.

BTW, what do you mean by "switch"? Fan switch?

 

Yeah, 160 deg fan switch.

 

Let me just clear something up really quickly, a colder thermostat couldn't possibly be affecting his start-up cold weather operation. Whether it opens @ 160 or 195 doesn't matter when the coolant is 120'.
I'm not a TBI expert, but rough cold running that dissappears when you youy warm up comes down to 2 basic causes.
#1- overly rich or lean. Either a bad injector, or perhaps a bad CTS. Unless of course you're far from stock and you're running a stock chip.
#2- mechanical failure. I've twice had blown head gaskets that would make me run like **** when cold and would dissapear once warm. What was happening is that as the metal heated and expanded it would close the leak. You can apply that principle to your whole engine. Your intake, or TB could have a loose bolt/crack that could be giving you a vacuum leak when cold. Unfortunately, i doubt whetever you're fighting would be really simple here. Since it is running like ****, that means teh vacuum leak must be isolated to one cylinder, or at least only a couple. Reason being, your TBI is a speed density system, so vacuum leaksd won't hurt anything unless it is right on top of a cylinder.
...ed

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Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

Here's a possibility. Are you getting a SES light and trouble codes? I had a 87 Grand Am with the 2.5 4cyl that also had TBI and had the same problem- ran real bad when it was cold. Turns out the Manifold Air Temperature (MAT) sensor went bad. Replaced it, about 20 bucks car was fine.

If that's it one ast word of advice- when you install the new sensor, don't overtighten it. I did, and crushed it against the bottom of the manifold. Had to buy another one.

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