Thread: GT engine trouble codes p0300 and p0108

Hi all,

this problem started about two weeks ago, I was headed to the gas station and didn't make it. My service engine soon light came on but it wasn't showing signs of any issues, so I did what most men in my position would do, curse at the ses light and do nothing. Then yesterday happened... I was headed to work and the engine started running real rough, it reminded me of when my old 89 bonneville's ignition module went out and it was running off of two cylinders so I called into work.

I took it into autozone and did an obdii scan which showed P0300 (random misfire) and P108 (map or maf sensor condition) I wasn't too thrilled.

P0300 could be:
-ignition system fault-spark plug(s), ignition wires, coil
-vacuum leak
-injector fault
-high or low pressure

P0108 could be:
-vacuum hose off, cracked, or passage blocked
-engine mechanical timing condition
-throttle body intake tube loose, off, or cracked
-BARO(barometer)/MAP(manifold absolute pressure)
-VAF(vane airflow)/MAF(mass airflow) dirty or defective

so here's what's been done thus far:
-changed spark plugs
-changed spark plug wires
-changed PCV

I found something that seemed wrong to me, the pcv valve and underside of the map sensor was coated with oil, and now that its replaced its blowing air out of it like an air compressor...am I missing something here? I don't have an issue buying a map OR maf sensor if they are the issue but I have three kids and I am the primary provider so the money is an issue...

Any thoughts or comments are welcome, thank you in advance!

I guess I should've specified vehicle, it's a 1999 Grand Prix gt non supercharged and no performance mods as of yet with 140000 miles, coupe if that makes any difference.

Spark plugs are ac delco rapid fire.

I still haven't driven it yet, kind off afraid too, the air that's flying out smells like a mixture of oil and fuel.

i also replaced the gasket because the old one fell into the abyss of my engine compartment

I made sure to push down and turn to put the map sensor back on the only possible thing wrong with that, that I can think of, is that it's not the proper gasket. I went to two local parts stores, in the woman's car, and neither one had the proper gasket so I bought an o-ring to fit it. This may be thicker or thinner than the original which could cause sealing issues. Is the stock part an actual o-ring or a flat gasket?

on a side note I'm a big fan of five finger death punch, I even got to talk to them on a radio show once! They're pretty cool guys.

Should there ever be oil on the back of a map sensor? I think that would harbor conditions which could cause a malfunction.

Getting ready to go the local pick a part for a map sensor and the correct pcv valve gasket, anything else y'all can think of that could be an issue and ill try to find it while I'm there. Thanks guys.

After changing spark plugs, plug wires, checking coil pack resistance, taking in ignition module for testing, changing pcv valve, map sensor, and fuel filter, I have thrown my hands in the air and decided to take it to a mechanic tomorrow.

I got rid of all other codes but the P0300, multiple random misfires, the only things that are likely to be wrong are the fuel pump, or the ignition module(as the tester never generates enough heat to provide a realistic testing condition)...or maybe it's the Pontiac emblem, yes that could be the problem. I'll update when I know for sure what's going on, maybe someone else out there in a RaceKar could use my story to get their RaceKar back onto the asphalt.

Yea let me know I'm having the same po300 code on my top swap. I've tried everything with no luck so far.

411.15 later and she's bangin like a champ. I had my ignition module checked at autozone and it passed a dozen times with no issue, but the guy said he wouldn't trust it because it doesn't generate the same heat which is what normally causes the problem. One coil pack was also bad even though the resistance test seemed positive, but who knows. So all said and done my GT got new spark plugs, spark plug wires, map sensor, pcv valve, fuel filter, ignition module, and one coil pack.

On another note I know the 411 seems a little high but they spent a while figuring it out, replaced the ignition module, a coil pack, two wiper blades, an air filter, an oil change, topped off all my fluids, and cleaned out my car. All in all five days and five hundred bucks and my car runs better now then when I got it. Hope some of this can help someone.

Ok thanks I'm going to keep trying but I can't seem to fond the problem.

I know it's a stretch but I know a guy with a fiero that was having multiple random misfires and it ended up that his fuel pump didn't put out enough pressure to satisfy the engines needs...if you've run out of other things to test, check your fuel pressure.

I tried that and had about 68psi with key turned on but not started. Whatever it is its causing the miss to jump from one cylinder to another.

That sounds like your ignition module. I took mine to autozone and it PASSED over a dozen times but it malfunctioned on the car due to heat. If you haven't replaced your ignition module yet, I would. And if the $145.00 is an issue, try the junkyard, it would be about 30 bucks but you would have an answer...supposing that module isn't fried.

Could be coil packs too. I resistance tested the primary terminals with a multimeter and it was within range, although 5 and 2 was lower than the others. And it got replaced too.

Best advice, take your car, a six-pack of PBR, and a sign that says "be gentle, I'm still new at this" to a mechanic you semi-trust and go from there. Best of luck!

Well i put my old ac delco spark plugs gaped at 50 and the misfire went away but still has a sputter if giving to much gas. I had autolites 104 gaped 55 maybe i gaped them to much?