Chevy 5.3 Random Misfire

[Coco]

I recently picked up a 2001 Chevy 1500 with the 5.3. The last week or so, while I am trying to get it to pass emissions and safety, it has been giving me a PO300 code which is random misfire. It only happens when it is cold out, and when the motor itself is cold. It also seems to idle a little rough when cold as well. Then after about 30 seconds it idles normally. One of my buddies is thinking it is the intake manifold ring/gaskets could be leaking, but before I tear into it, I want to see if anyone else happens to know what it may be? Any and all help is much appreciated! I got til the end of February to get it registered, but would prefer sooner.

 

[boogie_4wheel]

Get it warm, clear the code, then go get it inspected = Passed. Or does it do it during every start?

Check all the plugs; look for ash deposits (oil contamination). Could be intake gaskets; did you try spraying something flammable around the intake/head areas at cold start to see if it changes anything?

 

[Trate D]

I would 99% percent agree that it's intake gaskets or a warped intake manifold. It will cause a misfire when cold and seal up when it heats up. When it's cold and running use carb cleaner around the intake ports to see if you can pinpoint the leak. Usually just new gaskets will fix it. If you do them run a straight edge on the intake runners and check to see if it's warped, all of them have slight differences it seems but look for excessive gaps.

 

[Coco]

Thanks guys! It wont throw a code every time (also hasnt been as cold lately as it was last week for example) I cleared the code saturday, and the truck is still going through its readiness tests to be 'ready' to pass emissions. Until then, I can hook it to a machine all I want, but it is will just say not ready. I am thinking it is the intake too, I just wanted to get a couple more educated guesses before I tear it apart, and do it.

 

[UNSTUCK]

I'd use starting fluid to spray around the intake seal. If it leakes and sucks in some fluid you will hear the rpms pick up.

 

[B2-Bomber]

It's likely the intake manifold. It is a rampant problem. I've done several for customers. There is an update/upgrade manifold available. I slight mod is needed for the MAP, aside from that, it's direct bolt on.

 

[UFAB]

Make sure you are running oem plugs. Iridium. AC delco

 

[Coco]

Last night I replaced the manifold gaskets with the best version of fel-pros. No code this morning, and it was pretty cold, so I am hoping (fingers crossed) its fixed, and there isnt anymore issues. Only issue now, is the trans isnt shifting right, I think that has to do with the kick-up wire on the throttle cable.

 

[broncomitch]

I saw your old truck the other day...running grate...just saying lol

 

[Coco]

dont rub it in, I want that truck back more and more.

 

[Coco]

Thre another code today... PO122.... Shows TPS related code... Going to give it a once over, and check the trans shifting issue, as I think they are related, and something I may have missed last night.

 

[skippy]

You should buy Barts Duramax

 

[Coco]

I want another Ford It is tempting though

 

[Bart]

The TPS will play havoc with the shifting.

 

[Coco]

I reset the codes, and double checked the conections, it seems to be shifting good and everything now, so we will see what happens

 

[rondo]

My Silverado had something similar. Can't recall the code, but I found one plug with the insulator cracked. replaced all plugs and wires (it was due anyway) and it runs like a champ. not sure if that helps you or not.