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Shutter and flashing CEL on start-up

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ummandyea

New member
I have an 02 grand prix gt I bought a few months ago. Recently on start up the car will shutter pretty violently and the CEL will flash but after about 15 seconds it goes away and the car runs fine. Afterwards there are no codes, I did have an O2 sensor code but now its gone. I have not had a chance to check the basics (plugs, wires, etc) but just curious to see if anyone else has had similar issues or any clues as to what it might be. Thanks.
 


A flashing CEL may mean misfiring cylinder. Do you have any way to scan it when you first start it up?

I had a similar issue while running MSD wires. The car had no power and just shook while idling/driving. It turns out one of the wires had a split
 
I have a scan tool I can try and get a code in the morning. Not sure about the wires, whats weird is after about 15 seconds it seems fine I would think if it had a bad wire/plug it would always do it.
 
I have 3 stored codes P0141, P0140, and P0300. The first 2 are 02 sensor codes and the 3rd a random/misfire any ideas? Could they be related?
 
Yeah that is definitely related. Id start with the o2 sensors. It sounds like its your upstream based on the codes
 


Ive got a flow chart at home in one of my manuals for this issue. Ill post it up when i get out of work. FYI 1 am or so.
 
Flashing CEL indicates a potentially catalyst damaging misfire is occurring. If you just bought it I'd throw the plug wire heat shields away, install some new delco Iridium plugs (NOT Platinums- these cars do not like plats), some cheap lifetime wires and see what you get. I'd bet at least one of the wires is shot.

Easy way to check is to start the car up in the dark with the hood open and mist some water over the coils and wires. If you see blue or white spark then they are leaking voltage.

Also be sure that the wire for #6 isn't touching the O2 sensor in the rear manifold. And do one plug/wire at a time to avoid getting them out of order. These motors will run with wires reversed. Seen it happen often. The firing and wire order is here on the site if you search for it.
 


Might. I'd pull the slack out of that wire and get it off the O2. Even if the wire still looks covered it doesn't mean that it's not causing an issue. Even if the wires look "ok", they may be leaking voltage from old age. A lot of times when I find issues with wires they "look" fine, but upon further inspection they are degraded and junk, hence the spray test.

I dealt with a rough idle condition on my 00 GT and didn't have any codes, yet I could feel it. Once I did the spray test I saw that 3 of my wires were arching to the top engine mount nearest the coil packs. Replaced the wires and it smoothed back out.
 
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