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98 Malibu idle issues, ses light

8283 Views 17 Replies 2 Participants Last post by  Starship
I have a 98 Malibu LS 3.1V6, the car will not idle when in park or nuetral. The rpms consistently jump from 500rpm to 1100rpm back and forth and will sometimes completely stall out.

Also, only when the car is cool, it is somewhat hard to start. It only wants to start if I tap the throttle. Then, once started it runs very rough, like a severe misfire. But once I rev the motor up, it clears out. It does not do this if the car is warmed up.

If the car is in gear, it will idle just fine. And the car seems to run and drive normal going down the road. No actual misfires.

The check engine light is on. It is showing codes P0300 (multiple misfire) and P0401 (EGR flow insufficient). The plugs and wires look good, I have switched out the coil pack with a known good one, and put a new EGR valve on. No changes.

I dunno what to do next, I am suspecting the catalytic converter. Seems to have a foul smell from the exhaust, and a puff of blue smoke at cold startup leads me to believe possible worn valve seals may have caused failure of the cat.

What you guys think
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Also I have checked for any vaccum leaks and cant seem to find any. The intake manifold has all new gaskets as I just did that repair, but the car was acting in this same way before that repair. I did find a small port on the plenum nearest the power steering pump, to be capped off...I dont know if there is something that is supposed to go there?
I unhooked the MAF and that seemed to help out with the idle, steadys out at ~650rpm. But seems to cough and miss at idle in gear. Somewhat easier to start. And unfortunately I dont own a scan tool, I just had them run the codes at Autozone...
Okay so I installed a brand new MAF sensor today, and threw in a new air filter while I was at it. This seemed to allow the car to start easier, but the fluctuating idle, foul exhaust, and ses light are still existant. Not sure what to do next. For now I am going to return the new MAF, and get a vaccum gauge to check vaccum at the intake manifold.
I'll get some MAF cleaner spray, and some carb cleaner to check for leaks. A good scanner is definitely on my list, just waiting for the funds.

Erg...I just checked fuel pressure. Key on engine off it jumps to ~36psi. With car running at idle, pressure is only ~31psi. Hopefully it's just the fuel filter...
Alright, so this morning I changed the fuel filter. That didnt do anything, fuel pressure was still 31 at idle. So with the car running, I disconnected the vaccum hose at the fuel pressure regulator, and fuel is coming out of the regulator, at the same time, the fuel pressure jumps up to 40psi. Does this mean my regulator is bad?
Oh yea, new FPR and she runs like new. Thanks for your advice.
Unfortunately I am still getting code P0401 (EGR Flow Insufficient).

And also the ABS light comes on randomly. Seems like right before it comes on, I can feel the drivers front brake stop grabbing for a moment... here are the ABS codes I got:

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Where is the EBCM located??
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