Random misfire at idle and can't figure out what's wrong
#21
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In my previous experience, your car's PCM will not throw a random misfire code unless you are missing on multiple banks within a second of eachother. So normally you look at your factors that pull both sides of the motor together: battery power, fuel, and air.
Starting cheap and easy, my recommendation would be to have your battery tested at a parts store, and make sure your battery connections are solid. You could just have one bad cell screwing things up for the PCM.
Cleaning your MAF is a nice $10 fix... Good idea anyway.
Sometimes it's something stupid like water draining into the gas tank.
Keep us posted!
Starting cheap and easy, my recommendation would be to have your battery tested at a parts store, and make sure your battery connections are solid. You could just have one bad cell screwing things up for the PCM.
Cleaning your MAF is a nice $10 fix... Good idea anyway.
Sometimes it's something stupid like water draining into the gas tank.
Keep us posted!
#23
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When you say it happens randomly does this mean randomly driving down the road and stopping in traffic or randomly when starting up after sitting for a period of time? If it's the latter I would suspect head gasket. If it comes and goes while driving I would look at MAF & Crank Sensor. I had one at work that had 2 crank sensors (1at crank dampener & the other in back of block) and both were working according to my Tech2. On a hunch I changed the sensor in the block a BAM! just like that it started and ran great. These plastic sensors can have intermittent failures due to heat & moisture.
Good luck.
Good luck.
#24
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When you say it happens randomly does this mean randomly driving down the road and stopping in traffic or randomly when starting up after sitting for a period of time? If it's the latter I would suspect head gasket. If it comes and goes while driving I would look at MAF & Crank Sensor. I had one at work that had 2 crank sensors (1at crank dampener & the other in back of block) and both were working according to my Tech2. On a hunch I changed the sensor in the block a BAM! just like that it started and ran great. These plastic sensors can have intermittent failures due to heat & moisture.
Good luck.
Good luck.
Due to the seemingly randomness of this, I'm thinking it's got to be something PCM related. I'm actually about to drop it off at the dealer in just a few minutes. Updates to follow!!!
#25
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I got a call from the stealership yesterday and they said that it needed a new fuel pump and fuel pressure regulator. I wasn't too convinced that this was the problem due to the fact the fuel pressure at the rail was good but he said the pressure wasn't holding. They wanted $1100 to do the job. I laughed in his face when he told me that and asked when I can pick the car up. I spent $360 for them to diagnose this and I'm just hoping they were right. I just purchased a new pump and regulator from rockauto with shipping for $270. That sure beats $1100!!! Thanks again to everybody for all your help and I'm sure I'll be back when I have the next problem. I'll update as to whether or not the fuel pump fixes the problem. Fingers crossed.
#27
Join Date: Apr 2010
Location: Mentor, Ohio
Posts: 12,217
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I hope the dealership was right too. Piece of advice, according to the shop book, you should NOT need to drop the tank to get to the fuel pump. Looks like right behind the rear seat, in the trunk is a bolted in access hatch to service the pump!!
Best of luck, and keep us posted!!
Best of luck, and keep us posted!!
#28
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It's fixed!! I hate to say it but the dealership was right about it being the fuel pump and fuel pressure regulator. I checked the fuel pressure at the rail and the pressure was good which lead me to believe the fuel pump was good. It was a hard lesson learned but here is what I found out about fuel systems. Even if the pressure is good, which it was, the volume can still be low. Whether that was the cause or not, I don't know. What I also learned, and what was most likely the problem, is there is a check valve in the sending unit and if that gets crapped up, it will return too much fuel to the tank and in my case, caused a random misfire at idle. Chevy did do something right and there is an access panel in the trunk which makes it nice and easy to replace. If anyone else has a hellish random misfire at idle, throw a pump at it. You never know....
Thanks again to everybody for all your help. It's forums and communities like this that keep our hard earned dollars out of the pockets of thieving shops. Cheers. Ken
Thanks again to everybody for all your help. It's forums and communities like this that keep our hard earned dollars out of the pockets of thieving shops. Cheers. Ken