[&o]
Hi guys Im new here but im having a really annoying problem that keeps getting worse. The problem started just as the weather started turning colder, and there was high moisture content in the air. About 5 mins into my drive to work in the mornings, my engine would start missing at 2000rpm as I was getting onto the highway (without accessive throttle, just easing it) and between 65 and 70 mph. After another 10 mins it would clear up and drive just fine. This happened for about 2 weeks and only in the morning on high humidity/rainy days. One afternoon, after it had rained all day, the missing at 2000rpm happened on my way home from work and this time it shuttered violently and finally I got the SES light. Of course I thought this would be great because I could narrow it down.....WRONG! I took it to NTB to have the code read and got the best code you can imagine P0300. The mech. told me it meant multiple random misfire, I said yeah thats what I described when I walked in here. Anyway, now the problem happens every morning/afternoon that I drive no matter if its cold, wet, warm and dry. This morning I noticed something different, it did the usual miss at 2000rpm, but after the engine warmed up it was doing this surge thing: from between 1800-2300rpm my engine would surge as if the governor was kicking in, this was also noticeable on the tach, this cleared up after a few mins, and on my way home the SES light came on again but Im not willing to spend 96 bucks for someone to tell me what I already know. Please help me diagnose this and also explain to me what my engine is doing at 2000rpm to change the way it runs (just for my own knowledge). Thank you all very much in advance.

What I have done recently:

Tune up: New plugs (gapped properly)
New wires
New rotor
New Cap
New PCV valve
Last year:
Tranny rebuild
New Cat conv

 

I hope you don't mean you spent $96 to have NTB read that code for you. Advance Auto Parts will always do it for free!

Anyways, I'll occasionally have a similar problem on a day where the weather changed drastically with a large increase in humidity. I believe this increase in humidity affects the spark plugs in that the moist air dissipates the spark.

Don't worry, someone will chime in here soon and clear things up.

 

Yeah that is ridiculus I agree. I went to autozone but they said their reader was broken. I found out that a friend of mine has a reader so Ill get em read tommorrow unless it clears.

 

i had that same problem a while ago it happens to me on the morning but lately is been working fine but i still have no idea what the hell it is. i was getting a ramdom misfire codewell if u find out what it is let me know

 

I got the codes read again today for my SES light and yes again only the P0300 code.....Sheesh

 

same code i was getting

 

Did this ever get resolved? I have an almost identical problem. My truck idles fine, then kinda chokes at the 1-2 shift (didn't notice RPM) and starts the cutting out/misfire at a steady 1800-2100 RPMs. I have replaced plugs/wires/cap/rotor/intake gaskets/egr/coil but still no change. Unfortunately, this problem seems to have 100 different answers on this forum.

 

I have the same Problem on my 2000 TrailBlazer. It always happens in the morning when I am late for work.It pops a vaccum line off It looks like a PCV vavle not sure then it will run fine for a few days. I pretty sure it has something to do with moisture.

 

Anyone having a randome multiple misfire problem should start with this thread:
The dreaded PO300 CAUTION LONG POST

 

I've had basically the same problem with my 99 blazer 4.3 4wd. It turns out on mine, the tranny fluid was leaking into the transfer case slowly over time. I never got the PO300 code, but I had them read it at auto zone several times only to get no codes. I finally broke down and had the dealer look at it. They told me what was wrong the first time. Its nice to get it done for free at Auto Zone, but half the time theyre reader is junk and/or the employee doesnt know what the hell theyre doing