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Cold Start Misfire

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I have a '99 C2 with 67k mi. that I've had for about a year. The 60k service was completed by the PO.

I had an initial cold start misfire problem which resulted in a CEL with codes P0300, P0301, and P0303. Obviously it would run rough and if I could nurse it through the misfires (approx. 30 sec), it would be fine the rest of the day. Smooth through the RPM range and no codes or start issues.

I did some searching and ran through the misfire trouble shooting guide. The plugs look perfect, coil resistance within spec, but I found cracked coils, so I replaced all six. I cleaned all the connectors and made sure they all connected with a nice "click".

I'm still getting misfire codes, but now they are P0102, P1316, P1313, P1319 and P0306. Blinking CEL.

Again, this only happens during cold starts and if it gets throught the misfires, its fine until it cools down completely.

I'm narrowing it down to injectors, crank sensor, and/or coolant sensor, so any insight/advice would be great.

I only have an OBD-II reader, so my diagnostics are limited to the reader and a multi-meter.

Since May, I've done the RMS/IMS, replaced clutch/PP (May), addressed AOS coolant hose leak (July), and replaced a bad ignition switch (Aug). It's all been pretty straight forward and simple, but this has got me stumped.

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You need to research your fault codes:

P0300 Random Misfire Detected

P0301 Cylinder 1 Misfire Detected

P0303 Cylinder 3 Misfire Detected

P0102 Mass or Volume Air Flow Circuit Low Input

P1316 Misfire, Emission Related, Signal Implausible Cyl. 1-6

P1313 Misfire, Emission Related, Signal Implausible Cyl. 1-6

P1319 Misfire, Emission Related, Signal Implausible Cyl. 1-6

P0306 Cylinder 6 Misfire Detected

Obviously you are getting random misfires on one or more cylinder. Replace all your spark plugs, clean your MAF and throttle body, check your engine wire harness connectors for corrosion, run a tank with Techron. Since you replaced your coils, might be a bad one in the lot. Switch them around and see if you can isolate the bad one. Invest in a Durametric!

When your engine is cold it takes a lot more voltage to create the spark, hence weak or bad spark plugs with too much gap (don't chance it, these are cheap - throw the old ones out!), weak voltage to or bad coil, corroded engine wiring harness creating weak or random electrical voltage problems. Just my two cents....

Edited by DBJoe996
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I've ordered the plugs and will change them out. They looked just about perfect for 7K plugs, but it can't hurt.

I did research the fault codes and looked back at Misfire guide, but it pretty much tells me to look at what I already replaced (aside from the plugs). The new code was the MAF code and I plan on cleaning it this afternoon after I pick up a set of security torx bits.

What does "signal implausible" refer to?

You are right about the Durametric... I really need to spring for one, but I only have Apple hardware. They need to come up with an Ipad app!

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I'm betting on one or more bad spark plugs. Signal implausible - no reading (or from a human thought standpoint, unbelievable reading) either no feedback or outside range of acceptable values. Along with the security torx bits, pick up a can of MAF cleaner...works great! I love my Durametric...clear my stupid secondary air injector fault code all the time. Very good weapon in the toolbox arsenal...worth the piece of mind.

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I did check the coil connections this past weekend. Cleaned the connectors with contact cleaner and made sure they connected with a nice "click". Pulled the boots back to verify that the tab was locked in place.

The original plugs were tight and looked good (nice color and correct gap), but I just picked up some Bosch FGR-6-KQE to replace them just to be sure.

So my next step is to clean the MAF, replace the plugs, and R&R electrical connections associated with ignition.

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One more suggestion - while you are "under" there replacing plugs and checking connections, remove and clean up the engine block/frame ground wire. It's on the right side (passenger)...easy to find, knuckle buster to get off without some long extensions, but corrosion there could cause some intermittent/low voltage problems. Clean up the connectors and points of contact with some sandpaper.

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Out of interest do you know if it was the sparks of the MAF which fixed this. I had similar problem where the engine felt like it wasn't getting any air and you really had to rev it to get it to go while cold and the odd misfire many years ago on my Boxster (but I didn't check for error codes). This happened some time after I installed a pre oiled performance replacement air filter by K&N.

Someone recommended cleaning the MAF which I did and if fixed the issue for me.

Out of interest have you replaced the OME air filter with a performance alternative?

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