GM Truck Club Forum banner

1 - 2 of 2 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
I am a new member, I would appreciate any help. I have a 1996 Chevy Suburban with the 5.7 Vortec, K1500 4x4. Don't know when the engine was last rebuilt, but the truck has been to the moon and is on it's way back (258,000) About 2 months ago I started getting an intermitent P0507 high idle. That quickly esclated to misfires on cylinder 3 and 4. I changed the plugs and they had some light colored ash on them. Then it ran fine for about 3 weeks. At this time the high idle became constant. I cleaned the intake and changed the throttle position sensor. It got a little better. I bought a good Innova scan tool and found out that the EGR and CAT were not performing their self tests, so I changed the EGR. Now it runs fine if it's in gear, revs high in Park. If I drive slow for a long time and it gets really hot, it will rev high all the time. I did all the EGR resets (disconnected the battery, drove for the specific time at specific speed). I have also done the MMO in the tank, SeaFoam in the tank and flushed the intake (directly in it) with SeaFoam (with the old ashy plugs in it, then changed the plugs). I understand that the inner intake (spider housing) has a drain into cylinder 3 and 4 and that is why I flushed it with the old plugs in it. I also made a smoke machine and blew it in the intake and opened the throttle body all the way and got no leaks (unless its a vacuum leak in the innter intake????) I know a high idle is usually a vacuum leak, but there was no smoke anywhere.
1. If the new EGR and Cat are not self testing, could it be the onboard computer?
2. Could the spider injector cause this? I know these are a common problem.
3. Could the ashy plugs be a timing problem? I had mechanical oil pressure indicator put in about 3 months before this and the mechanic had to do a lot of disassembling at the back of the engine to put it in (there was a short in the dash that affected the CD player and oil pressure indicator in the dash, so I just pulled the fuse on teh CD player and put in a mechanical oil pressure indicator)
3. ANY HELP WILL BE APPRECIATED. Thanks greg
 

·
Registered
Joined
·
269 Posts
Funny you mentioned the dismantling of the engine, because I was thinking the ash and the high idle could be related to a leak somewhere... possibly letting extra air into the cylinders you mentioned. Doesn't it sound like a possible lean issue? Don't take my word for it, though... I'm just guessing off of the minimal amount of info you gave and the minimal amount of knowledge I have.
 
1 - 2 of 2 Posts
Top