1999 Vortec 454 Rough idle

[montess85]

Having a hell of a time figuring this out. My truck has had this rough idle since I bought it. It idles rough and stumbles until it gets about 1500-2000 rpm. No engine codes are stored. It did have a hard time starting and backfired a little a few times but it hasnt done that again. It only popped a little but I could hear it. It was a cold start when it did this. It seems to run ok every once in a while at random. Still not 100% but better than normal. Here is what is done to the truck.

Fuel Pressure Regulator
New 98-00 LS1 injectors
Plugs
Wires
Cap
Rotor
Fuel FIlter
Fuel pump
Ive swapped out the MAF with a know good one

Still has the same issue. I though for sure after changing the regulator and injectors I would solve this. The old ones were rusty and the nozzles even looked rusty, but still the same issue. I have access to a scan tool and I have checked the history codes. Nothing there. The Long term fuel trim is off. Its -15 on bank one and 11 on bank 2. What am I missing. I have looked for vacuum leaks as well and cant find any. Any ideas

 

[Mangonesailor]

I thought there was a way to disable the IACV and spray ether to find vacuum leaks easier. What are your O2's telling you? How many miles? This is the 454 in your 'hoe, right? What injectors were in there before you changed them and, if they were different, did you re-tune? What fuel pressure are you running? Have you performed a leak-down test?

Unrelated: What headers do you have? Is your truck 4wd or 2wd?

 

[JScott23]

If you replaced MAF, Cap, Rotor, Wires Plugs, Fuel Pump, Fuel Filter, Regulator, & Injectors. The only other thing i could think of would be the o2 sensors... there is a pre and post cat o2 sensor for each side.. also the cats can become clogged easily, the only other thing could be that the distributor itself is bad. I can't think of anything else..

What's the engine's mileage? Mine is at 204k and has issues with stumbling at low RPM idles and doesn't want to rev past like 2k. I'm doing plugs wires cap & rotor this weekend.

 

[brycebba]

I have been plagued with problems like this for months. I also bought ls1 injectors and the first set they sent were an old style and didn't run great, second set has had 2 injectors go bad in less than 3 months. These were said to be new but I have my doubts. Basically don't be so sure it isn't a defective part... Especially the injectors since they are a common cause of that problem. Any hard start issues?

 

[montess85]

My truck has 92,000 miles. And sorry its not my Tahoe. Its my 1999 K2500 CCSB. Its starts right up most times. Had a couple hard starts with some backfires out the exhaust. Today took it for the first drive in about 2 months. Now it spits and sputters under load. Pops and backfires as well. Seems to get worse when it warms. I checked the Cam retard and its at 8-9 . Isn't it supposed to be + or - 2 ?

 

[montess85]

Also it had the factory injectors in it. I was told they were changed by the previous owner but they were pretty rusty so I have my doubts. I also changed the O2 sensor on bank one. I had a lean code bank 1 sensor1. I put the O2 in and did the tune up along with the injections and the FPR. Code hasn't come back. But it still runs like craps. Prior to all that work the Long term trim was pegged at -25 on bank 1.

 

[montess85]

I wish I checked the dam distributor when I had everything apart. I keep reading the gears are know to go bad.

 

[JScott23]

I was told that you can try and twist the rotor side to side and if it moves easily the distributor is bad.


Thats a wierd problem with a engine with 92k..

 

[montess85]

Going to pull it apart tonight to check. Along with du checking my other work. Maybe I missed something.

 

[JScott23]

Good luck!