coldharbor

This is so strange...I have been chasing a P300+ series of codes for a year now. The car throws the misfire coded every 3 or 4 days within the first 30 seconds of start up. The garage said at first it was electrical. Then they said it was a valve geometry problem. Let's take the head to a machine shop. I have hesitated to do this. I was driving the last two weeks and got the occasional P300+ codes and cleared them with my Automatic dongle and iPhone. Three days ago another code threw and I drove for 2 days. Tonight I started the car and no code, no engine light is on???? What has happened? This is a daily driver, never a loss in mpg (around 28 to 30), 2002, with 80K miles. It is around 0 degrees here in Cincinnati right now. Is this a 'ghost in the machine'?

Slowcrash_101

Check valve clearance before you start taking stuff apart.

B serious

A compression test would be a good idea. If the engine has a loss in compression, it could be causing a misfire that is on the very cusp of detection.

Also...spark plug condition, fuel injector condition, coil pack condition etc.

Simple stuff first. Start with the compression test. This will allow you to check the spark plugs and coil packs visually as well.

coldharbor

Thanks for the feedback. The garage did all of those things (spark plugs, coil packs, valve adjustments) and didn't charge me! The compression and leak down were fine. Their last recommendation was to investigate valve geometry at the machine shop - $1300+ to start. As I mentioned, subsequently, the car threw misfires which I did not clear that day. The next day on start up, fully expecting the engine light to be on, the engine light was not on, I had NOT cleared it. It has not come on since. I had been throwing misfice codes for over a year. Obviously as a non-mechanical person, I am highly puzzled by this turn of events. How likely is it for an engine light warning to clear itself? My intuition tells me it is not likely, at all.

notaloafer

I can shed a bit of light on the whole "CEL clearing itself" issue. My car would throw a misfire every now and then, and after awhile it started happening more and more. I would clear them sometimes and throw in some fuel injector cleaner, and it would stay away for a few thousand miles. One time I started my car and had a flashing CEL - on which I did an immediate shutdown. When I turned the ignition to ON again, the CEL was absent. I'm not sure how the CEL works in this car, but mine has definitely cleared itself on more than one occasion too. I heard someone on here say that if you go long enough without a misfire/issue, that the CEL will clear itself. This also worked in my case where I replace and o2 sensor and after two days of driving the CEL cleared itself too. Another flashing CEL issue was when I swapped batteries. The Engine Computer had to re-learn the timing/retard and it did a couple of flashes before clearing itself and going back to normal again (ANYONE correct me if I'm wrong on this one, it's just my experience!).

My guess for you - get those injectors cleaned! It's $60 to have them cleaned professionally (check my recent threads, they mention the name of the guy on here who does it) it is only $60 (all 4, including return shipping). It's a cheap investment that may axe your issue. I simply have been putting it off by using overzealous amounts of injector additives (TECHRON TECHRON TECHRON!)

I've had random misfires the last year or so too. I keep it at bay with Techron fuel injector cleaner. You might try throwing in some fuel injector cleaner as a test (one set every tank for a few thousand miles - you can buy a 6 pack box at Costco for pretty cheap). The first time do a double-dosing of it, drive till empty, then do one bottle per tank. See if the CEL comes back.

Hope this helps.

PS - I also have good mileage, and had done a recent valve adjustment myself. I know those aren't my issues. My spark plugs are near-new too.

coldharbor

Thanks notaloafer. I will do this.

coldharbor

2 tanks of Techron...still getting misfires...occasional bogging when ambient temperature goes above 40.

notaloafer

Wadzii is the guy who cleans them on here, something very cheap to try. I turned out on mine that I had coils that were just taking a year to fail. I read on here that they only last around 100k miles usually, abd I'm at 140k now.

Slowcrash_101

check signal from ecu, unfortunately the ignition module is in the ecm, I say try using a known good computer and see if that helps.