Tech2 or others,
Any thoughts?

I've now had the knock sensors and camshaft position sensor swapped out today (another ~$800) and misfire is still there.
I've now had 2 diffrent mechanics give it a good review and diagnostic, changing out what they suspected was 'surely' the problem, and still lack of success... I am starting to get frustrated with this thing, could really use some help.
This is my family hauler, I need to get this thing working right (all 3 kids don't easily fit in my saab with car-seats that are required these days).

 

The only codes set are p0300 and P0301?

there is a few tsb for this concern. One involves wiggling the ignition coil wiring in an attempt to duplicate the misfire. If it does, there is a ignition 1 power to the coils wiring problem.

 

Take it to the dealer, I have had about 3k worth of work done to mine from TSB's all for free.

 

I wonder if the AFM (active fuel management) system could have anything to do with the misfire?

 

Tech2, correct, the only codes I have ever gotten are p0300 and p0301, I have yet to get a more 'useful' (specific) code pointing to a single cause like a knock sensor code. I was wondering if you could clarify which wires you're talking about wiggling, the harness coming in to the coil pack? The one with 4 wires? I have wiggled all of those over the past few weeks, even did the coil pack disconnect to see if I could determine which cylinder was misfiring.

JWeezy, I fear with nearly 120k on the odometer I would be past any opportunity that the dealer (GM) would cover the cost of repairs at this point...

in2pro, AFM? I thought AFM was the cylinder deactivation that started with the newer body style... I know I don't have the cylinder deactivation. If you're speaking about something else, I'd like to learn more.

Possibly new bit of information. The issue is immediately detected upon starting the car. Depending on 'the day,' when you start the car, you can immediately tell if it is going to run well that day or not based on the initial idle and how it feels. It will feel the same way the entire time it's driven. Even on it's best of days, there is still a low idle and you can feel some misfiring but some times it is much rougher than others, and it feels that way if it's a 5 minute trip to the grocery store, or a 5 hour trip into another state. I'm trying to narrow it down to if it can be a single key-on event during a day or not (ie if it can change if you turn car on and off, if something would 'reset' and drive better). No luck there yet.

 

Don't call me crazy because I have to maintain a Volvo and I have seen MUCH crazier than what I am about to suggest...

Do the two different conditions, running well or not, depend on which key is used to start the 'burb?

I have seen something "similar" (and not valet mode) on a Volvo. Add to that, on my 'burb, one key will unlock the cylinder for the spare tire lock and one will not, both original OEM keys that came with the 'burb new and I have been assured there is no valet or other difference in the keys delivered with Suburbans of that year so like I said, don't call me nuts just yet.

 

DPLarson
I don't think you're crazy at all... this is exactly the type f thinking I was looking for. I have had issues like that before, with other cars.

In this case, no, the key used makes no difference. Both keys (now 3, I had a spare key cut in addition to the one for wife and me) have the same issue, cause same symptoms.

Additional testing done: Had cam-lobes checked, they're fine. This was suggestion my mechanic checked based on IATN posting he put out about my car (4 of 10 mechanics that came back with suggestions had their issues resolved with cam lobes worn).
I'm gonna try to check for a wiring/grounding issue a bit next chance I get...(start measuring continuity in harnesses)... still open to any other suggestions you all come up with out here.

Thanks!

 

I was wondering if OP has found/isolated the problem.
I recently bought a 2006 Suburban and replaced the engine with a ued engine, which is suppose to have only 57k miles on it and have the exact same issue. I do not feel anything at normal driving speed, just some stumle at idle and when you first start moving the car and have been getting pending codes P0300 and twice got the P0308. I also had the check engine light come on twice for P0300.
Honestly I don't think the engine has only 57k miles on it, the shop lied too many times, when asked specific questions. In any case the guy is telling me to replace the throtle body, which is electronic in this car and this will solve the problem. I used a fuel injector cleaner and since that treatment the stumble is less but still present. I have an OBD tool attached all the times and am not getting any more misfire codes but the stumble at idle and when I first get going persists.

 

Welcome to the forum.

Might check the fuel pressure. Sounds just like my '87 IROC-Z when its fuel pump was on its way out. Could hardly get going from a dead stop but once up to 30 mph, it would go like a striped *** ape.