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Misfire on cold starts

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jakk220

10+ Year Contributor
1,319
312
Nov 13, 2010
Akron, Ohio
Ever since my cars rebuild, it has never really idled right on cold starts. It was always a little bit choppy at about 800 rpm with a target idle of 1000. I would expect it to idle high on a cold start but it doesn't. Just a few days ago I put on an AEM fuel rail and it seemed to agitate the issue. Now it wont stay running hardly at all on a cold start and I have to keep my foot on the throttle to keep it running. If I drive the car it misfires extremely bad and sounds like a Subaru until it gets close to op temp and even then feels sluggish in the lower rpm. The only thing i noticed when i looked over the log is that my O2 seems to be reading lean in open loop, and then right when it went to closed loop, the idle shot up to 2k and then the O2 voltage dropped way low and the car started idling horribly again. unfortunately I do not have a wide band though. Can someone please look over the log for me and see if anything looks messed up? I don't want to do anything to hurt the new motor. Thanks
 

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  • log.2012.06.14-01.elg
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Sorry im no good at reading logs. Have you gone through the check list LOL? Plugs, wires, coils, boost leaks, vac leaks, compression test, CAS, Timing, ECU, Injectors. Are you thowing any codes? Could throw in a new front o2 and see what happens.
 
Some of them yes. Injectors are good I know, compression should be good its a new motor but haven't tested it, ecu was tested when I got link about 2 months or so ago, plugs are new, CAS is good, and its throwing a random misfire code and a MAP sensor code that's always been there.
 
The behavior sounds like a bad coolant temperature sensor. Do you know why it's throwing a MAP code? Possibly something there as well.
 
The map code is because of my egr block off and evap canister delete I believe. However if the sensor was bad it wouldn't effect performance to my knowledge. And unfortunately I do not have a wideband yet. I had to spend so much money on other things with the car it was at the bottom of the list. Like I said tho the o2 sensor is reading like 0.2 to 0.4 in closed loop, but cycles when driving. Bad 02?

Wouldn't a coolant temp sensor throw a CEL tho?
 
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