Seems to me that the only way to get a backfire through intake system is
either a stuck valve :(, or the ignition timing is off due to
malfunctioning computer or sensors. I saw a number of posts recommending
sensors to check, but how about the MP SBEC? If you still have your
stock SBEC, you might try swapping it back in and see if the problem
remains. While your at it, you might check that all of the connectors to
the SBEC look clean and are firmly attached.
jeff
98 RC 4x2 V8 5spd 3.55SG flares
Michael Clark wrote:
>
> Hey guys I was wondering if anyone would have any ideas for this. I
> have a sporadic rough idle that usually occurs after a warm restart
> (usually after the engine has cooled down for about 45 minutes or so,
> and then started back up). But the other day it did it from a cold
> start. The magnums have a rough idle to begin with, but this is way
> more. When it happens the idle will get VERY rough and labored, I guess
> a way to describe it would be that is sounds almost like it has a full
> race cam. It will make a loud sucking sound in the throttle body (I
> believe this is the AIS motor opening all the way up to keep the engine
> from dying, but not sure) After 20 - 45 seconds it will clear up like
> someone turned a switch off and idle perfectly normal. Now if you try
> to drive it during one of these rough idle episodes it will hesitate,
> surge, and sometimes even backfire (through the throtle body) then after
> that everythings fine.
>
> To date these items have been replaced to try and correct this:
>
> new AIS motor
> new EGR valve
> new O2 sensor
> cleaned the throttle body (thouroghly cleaned it inside and out)
> new throttle body gasket
> new fuel filter
> new plug wires
> new cap and rotor
> new plugs
> couple dozen bottles of fuel injector cleaner
> switched back to stock computer, still did it
> No trouble codes
>
> I have run out of ideas of what it could be. Right now I'm thinking it
> may be an injector sticking open, or maybe even a valve sticking, but I
> really have no clue. Any ideas on what might cause something like
> this. Fuel pump? Intake leak? After it clears up, it runs as good as
> the day I drove it off the dealers lot, so I don't think it could be
> anything major (at least I hope not). Seems to me to be something
> electronic, but what?? Any help greatly appreciated on this. The
> dealer will be the last step, but I'm sure they will blame my bolt-ons
> for the problem. Oh yeah, it did this once before with stock exhaust
> manifolds, so headers are not it....
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