This just started about a week or so ago and it does not do this all the time.

The problem seems to happen when the air temperature is at or below 40 degrees. I start the car, and the best i can describe it, is it sounds like a pulsating miss. If you give it some rpm it, just sounds awful. But, as you let it idle, for a couple minutes, it smoothes out and eventually runs normally.
Turn it off, and start it again, nothing. Runs fine.

What gives?

 

Could be a sensor. IAC, IAT, MAF, MAP, or coolant temp sensors. It wouldn't be the O2 sensors. It almost sounds like something is not reading the air right.

Could be exhaust or vacuum leaks especially vacuum leaks at the intake manifold. As the engine area gets warmer, metal expands, and it could close up the leak.

Check the plugs and wires too but kind of doubt those are it.

 

Those sensors can all be tested with a volt meter right?

 

Coolant can and IAT can. IAC can too.

http://shbox.com/1/4th_gen_tech2.html#ect
http://shbox.com/1/iac2.jpg

MAP and MAF will probably jump around too much on the readings to know whats going on. You can unplug the MAF and start up the car, it will run in speed density mode without the MAF, if it still runs the same crappy way then its not the MAF(Mass Air Flow sensor).

MAP you'll probably have to swap out with a new one or one from your old engine harness, any 1 bar GM map sensor will do. Its the sensor that looks like a domino on the intake manifold.

 

Ok. Thanks for the tips. I will let you know what I find.

 

ok heres what ive done.

Today i thought i would check the maf, so after the car was warmed up, i unplugged the maf, nothing happened. I went for a drive, drove exactly the same, so im thinking ive got a bad maf. I go to napa, get a replacement maf, install it, and now when i unplug it it almost stalls completley then resumes idle (cant really tell if its any worse, the car is pretty lopey when running normally). The car ran great on the way back to the house.

i changed my oil, and now the car runs like complete garbage. It runs what smells like VERY rich, and when you start it when its warm, it idles high (about 1500) for about 20 seconds before it comes back down. The idle isnt as smooth as it was, but it was never that smooth anyway due to the cam.

The only thing i can think of that might of chaged is this: The passenger side o2 sensor is in an inconvient place (due to my lack of test fitment when installed). When the car is jacked up the lower a arm comes down into contact with the very end of the sensor. My sensor on that side is bent at the end, and the little plastic ring that goes around the wires is coming off. So my thoughts are this sensor might be bad. But i am unsure if a bad o2 would cause these problems.

The car has about 1/2 the power it normally has. Keep in mind the car does want to fall on its face when the maf is unpluged.

I cant tell you about any codes as i dont have a scanner.

 

Autozone or other parts stores might do a scan for codes for free. Maybe call them up and find out.

 

Do you have a basic tune? Did you change anything really recently?

 

I have a mail order. Nothing changed recently other than the new MAF. Autozone and such only scan obd II ive tried. Could the o2 cause what im experiencing?

 

Oh yeah, the porcelain on a spark plug cracked and half fell off. So I'll be replacing that.

 

Shouldn't be the O2's. The computer doesn't start reading the O2's until about a minute or 2 after it starts and also not until the engine reaches like 130 degrees.

 

Changed the plug. Turns out my maf is fine. I just had 2 plug wires crossed. Its running normal again but that still leaves the cold start problem. for the heck of it I checked my fuel pressure, it's 38psi at idle and 42psi at wot.

The problem hasn't occured since I first posted about it, but I'm going in for a dyno tune this weekend and would like to make sure it's running properly.