Have a 98 1500 (360), its fine at start up but after running a few minutes (varies) it starts to sputter and sometimes backfire, also get a loud vacuum sucking sound. Only last a few seconds to minutes (varies of course) then is fine again. Doesn't always do it but most of the time, anybody have any ideas? Doesn't make idiot light come on but my thinking is a questionable ECM or body control mode? Any and all help greatly appreciated.


On a side note is there a ground on passenger side around the kick plate thingy? or behind glove box area, still have some gremlins in that area.

 

The vacuum sound is normal, its the IAC allowing more or less air into the throttle body. You could have a plugged cat, remove the front 02 sensor and see if the problem gets any better. Have you checked for a blown plenum gasket ?.

 

I'll try the 02 sensor and see what happens, haven't really checked anything yet, would be surprised if plenum gasket is bad because is runs fine (actually great) except for those few seconds/minutes when its not.

 

Try disabling the front O2 sensor first. (just unplug it) See if that makes a difference.

 

I have the same problem on my 98 1500 5.2l. When this happens the short term fuel trim on my scan tool goes down to -33.6% Front o2 reads .900 rear is .120 Seems to not stumble as bad or at all if I run the air conditioner at startup. Truck runs great after 5 mins. Should I replace Front o2 senor or look somewhere else?

 

Sounds like the front O2 isn't getting ready fast enough, maybe the heater has gone bad/gotten weak, or some such. Unplug it, see if the problem goes away. If it does, replace it.

 

Before I could unplug the front o2 sensor I ended up getting a p0132 code. I disconnected it this morning and seems to be running a lot better. My question is it ok to drive without it for a week? I only drive around 25 miles a day. Thanks

 

Yeah, it won't hurt anything, it'll just run a little rich with the O2 unplugged.

 

Just changed my upstream o2 today.. I had similar problems and all is good now. My truck is a 97 with 318 but it needed the 18in wire... I made the 12in work and saved $30