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PO300 Code on 2001 Mitsubishi Eclipse GT Spider: Causes and Fixes

Model: 2001 Mitsu Eclipse GT Spider Fault Code: P0300 Posted: 2008-08-25 17:47

I'm experiencing a random multiple misfire (code PO300) on my 2001 Mitsubishi Eclipse GT Spider. I recently had a major tune-up about six months ago, including replacement of the distributor, PCV valve, spark plugs, and ignition wires—all of which appear to be in good condition. The issue only appears under certain conditions: it doesn't occur when the engine is cold, and I don’t notice any drivability symptoms such as hesitation, poor acceleration, or rough idling. My fuel economy remains excellent, and the car feels responsive. I'm wondering if the Powertrain Control Module (PCM) could be causing this issue—especially since it's not triggered under cold starts. The problem started after my tune-up, which makes me suspect a possible ignition system fault despite the replacement parts. I have no budget for further repairs and need to identify the root cause quickly because my registration is expiring soon. Any insight into common causes of PO300 on this specific model would be greatly appreciated.

Related fault codes
P0300
Comments (6)
Anonymous 2008-08-26 10:26

Has anyone else encountered a PO300 code on their 2001 Mitsubishi Eclipse GT Spider? What were the root causes?

Anonymous 2008-08-26 11:51

There are numerous potential causes for a PO300 code across different vehicles. For a specific diagnosis on your 2001 Eclipse GT Spider, it's best to consult dedicated forums or check manufacturer service records. Was the PO300 present before the tune-up? Are fuel pressure, ignition timing, EGR function, and other key systems operating correctly?

Anonymous 2008-08-26 12:04

Jeff Compton wrote: There are numerous potential causes for a PO300 code across different vehicles. For a specific diagnosis on your 2001 Eclipse GT Spider, it's best to consult dedicated forums or check manufacturer service records. Was the PO300 present before the tune-up? Are fuel pressure, ignition timing, EGR function, and other key systems operating correctly? I understand that—thank you. The code did not appear prior to the tune-up. I’ve already had the ignition timing checked, but everything else is too expensive for me to continue repairing. I’m hoping there’s a common, affordable cause behind this issue. Notably, I don’t feel any drivability problems—the car runs smoothly with great fuel economy and no hesitation.

Anonymous 2008-08-26 12:06

Since the PO300 appeared after your tune-up, it's still worth suspecting faulty ignition components—even if they were new. Could be incorrect spark plug types or poor installation quality. While it may be costly, contacting the dealership might help identify known issues on this model. If others have faced this code on a 2001 Eclipse GT Spider, their experiences could provide valuable insight.

Anonymous 2008-08-27 04:56

Jeff Compton wrote: Since the PO300 appeared after your tune-up, it's still worth suspecting faulty ignition components—even if they were new. Could be incorrect spark plug types or poor installation quality. While it may be costly, contacting the dealership might help identify known issues on this model. If others have faced this code on a 2001 Eclipse GT Spider, their experiences could provide valuable insight. I'm going to visit the dealer this Friday—it will cost $80 just for a diagnosis, but I'll do it anyway.

Anonymous 2008-08-30 15:44

I finally found the cause: two issues. First, my gas cap was faulty—AutoZone staff didn’t provide the correct type for my Eclipse GT Spider. Replacing it fixed half the problem. Second, I discovered that my ignition wires were worn and degraded. They’re being replaced this week. This combination resolved the PO300 code completely.