97 suburban missfire p0300 code

[GreaseMonky81]

Ok I have a 97 suburban 1500 4wd, w/ 5.7l and for awhile now I have been getting a -p0300 code-. it started out as a another p03.. code i belive it was seven, and since it has been just the random multiple cylinder misfire. It seems to run rough only when its cold. like you first start up it dosent do any thing, but back out of the drive way and take off, it hesitates and surges, during crusing and normal acceleration, but not under full acceleration. It goes away once it warms up it seems. It started after I installed a superchip powerprogrammer, within days. plugs were done last year along with cap, rotor, wires, and fuel filter. I have also changed water pump ( year ago), fuel pump a few weeks ago, heater core, I smell antfreeze, somtimes since it was bought 3-1/2 years ago. Have changed radiator 3 years ago, rebuilt rear end, 6 months ago, gov lock came apart, I have noticed that the collant line behind alternator, is leaking, whent to the parts store and the gave me a piece of hose and said that was the replacement part, so I am still checking that since it dont look the same. I have read severla posts but none with the exact same syptoms, some one help before i go insane

[wafrederick]

It could be a worn out distribitor gear.GM does have problems with the distribitor gear.Pull the distribitor out and inspect the gear,look for shiney spots on the gear.Mark the distribitor before pulling out,the timing is not adjustable and the distribitor has to be set with a scan tool.The coolant leak could be the intake gasket.Fel Pro has an updated intake gastet set,part no. MS98000 T.The updated ones from Fel Pro are made out of metal with rubber sealing areas instead of plastic

[chuck's]

With the vehicle acting up when it is cold and seems to get better when warm,I'm wondering if the temperature sending unit may be giving a false signal to the computer. The sensor is saying the engine is cooler than what the engine really is.When cold, the engine gets a richer mixture than when it is warm.I hope this will help your problem.
chuck's

[97Burb&99Sierra]

May want to also check the throttle body and fuel injectors. We got this code several years ago, and it ended up being a bad injector, and the throttle body, intake manifold and plenum were all gunked up. Fixed at the dealer many $$$ later. My research at the time and since have shown this to be a common problem.

As far as the leak goes, that could be the heater quick disconnect, connected to the front left side of the lower intake manifold, just behind the alternator. That connection is made out of a very brittle metal that will fail after a few years of dexcool flowing thru it. Also relatively common from what I've seen.

If this is what is the matter with your 'burb, they could be connected problems. If the qd is leaking, that coolant (dexcool = very corrosive) may be getting onto the intake manifold gasket and causing its decay. There is a good thread on this forum for fixing it: http://www.automotiveforums.com/vbul...d.php?t=441290
I did this a few weeks ago -- cleaned everything out really well, the leak has not returned and everything is running smoothly.

Hope this helps, and good luck.