rough idle

[Specialist]

im having issues with my idle it seems to miss and is lacking in power when i hit the throttle in gear it stumbles and whenever it spools the miss goes away but will only go to 4100 rpm checked everything and the only thing thats getting a good amount of vacume is the fuel reg its got new plugs wires cap & rotor msd blaster 2 coil iridium plugs it feels like a massive slip at high rpm like it wants to fall on its ass ANY HELP WILL DO! im drained and about ready to sell it if you dont have an idea and are willing to make it your problem ill take 6000 for it

 

[Quickstop [UK]]

Re: rough idle

Sy or Ty? where?

What have you done to it? no vacuum is going to make life difficult. new vacuum lines sound like the first port of call then the usual stuff - wires, cap, rotor, plugs etc etc.

 

[Specialist]

Re: rough idle

fairbanks alaska syclone

 

[davkat]

Re: rough idle

Had a similar problem with mine. All my vacuum lines were okay, also changed to NGK UR5 plugs (haven't had much luck with iridium) and checked the timing which was too retarded. After that those problems went away. Good Luck.

 

[Nitrous]

Re: rough idle

I have a similar issue, I completed a tuneupwith new cap, rotor, ur5 plugs gapped to .035", new fuel filter, new plug wires, pulled and cleaned TB and replaced gasket, replaced IAS and I cleaned the injectors through the rail, set Accufab fule regulator to 50psi and set timing at 0. I now have a slight miss at idle that drives me crazy with a 200 rpm swing. I would almost swear it's a vacuum leak but I've pulled everything and replaced most of the lines with new. I haven't replaced the turbo yet but the tips of the compressor blades are broke and I'm sure this has changes the amount of air entering the intake which could possibly change MAP pressures but I haven't looked at the MAP yet. I'm gonna have to purchase a scanner and tuning S/W to get things running correctly.

 

[turbodig]

Re: rough idle

I have a similar issue, I completed a tuneupwith new cap, rotor, ur5 plugs gapped to .035", new fuel filter, new plug wires, pulled and cleaned TB and replaced gasket, replaced IAS and I cleaned the injectors through the rail, set Accufab fule regulator to 50psi and set timing at 0. I now have a slight miss at idle that drives me crazy with a 200 rpm swing. I would almost swear it's a vacuum leak but I've pulled everything and replaced most of the lines with new. I haven't replaced the turbo yet but the tips of the compressor blades are broke and I'm sure this has changes the amount of air entering the intake which could possibly change MAP pressures but I haven't looked at the MAP yet. I'm gonna have to purchase a scanner and tuning S/W to get things running correctly.

Turbo blades have nothing to do with how it idles... the throttle plates are closed.

Idle issues boil down to vac leaks, IAC, or a bad tune in an aftermarket chip.
You won't always find leaks externally, intake manifold gasket issues are not unusual. I've even seen porous intake manifold castings cause that issue.

 

[Nitrous]

Re: rough idle

Ok, makes sense but I wasn't sure the blade positioning since I can't datalog yet and I'm new to the 4.3 fuel injection. The tune ran fine with the Ultimate chip before the vacuum line replacement and I did spray around the intake to see if there was an increase in idle but found nothing. Another thing, when cold the idle is great and once warm is when the problem starts. Thanks for the reply turbodig

 

[Don W.]

Re: rough idle

Long story short I fought an erratic idle for a long time. Turned out to be the lower (valley) portion of pas side intake. Fixing that cured a bunch of stuff.

 

[HiPerformanceHill]

Re: rough idle

Check your fuel pressure especially at WOT. If its bogging at high rpm it maybe running out of enough fuel pressure? If so maybe your pump is weak. I only say this because that is a separate issue from idle issue. I had some issues in the beginning with mine. My fuel pressure was good. But you didn't mention whether you tested your FP yet. On mine I found a bad coil post and the cap and rotor where bad. My timing also had been retarded about 2-4 degrees as well by the previous owner. Hope this helps.

 

[turbodig]

Re: rough idle

Ok, makes sense but I wasn't sure the blade positioning since I can't datalog yet and I'm new to the 4.3 fuel injection. The tune ran fine with the Ultimate chip before the vacuum line replacement and I did spray around the intake to see if there was an increase in idle but found nothing. Another thing, when cold the idle is great and once warm is when the problem starts. Thanks for the reply turbodig

Makes sense - cold, the ECM is running open loop, and is typically richer than average. Once it warms up, closed loop fueling takes control, and usually leans things out a bunch.

I've chased these problems on dozens of trucks for many years, and invariably, we find a vacuum leak someplace.

It's little consolation for the guy trying to find it, but that's the way it plays out.

 

[NecroWolf]

Re: rough idle

im having issues with my idle it seems to miss and is lacking in power when i hit the throttle in gear it stumbles and whenever it spools the miss goes away but will only go to 4100 rpm checked everything and the only thing thats getting a good amount of vacume is the fuel reg its got new plugs wires cap & rotor msd blaster 2 coil iridium plugs it feels like a massive slip at high rpm like it wants to fall on its ass ANY HELP WILL DO! im drained and about ready to sell it if you dont have an idea and are willing to make it your problem ill take 6000 for it

if the only thing getting good vacum is the fp regulatoer i'd start there either get one of the vac line kits or make your own. there are numerous baisc meatience issues that could cause what you're describing. take your time and test before you replace. i had a rough idle then a no start problem when i got my swap running and it turned out i'd burnt the spring loaded contact for the coil to the rotor bug had melted and the cap/rotor had about five hours total on them.

 

[Nitrous]

Re: rough idle

I didn't mean to hijack this thread but you can never ask for enough info. Martygar8 had a similar problem and itt turned out it was his lower intake. I'll go back through the vacuum lines and if I can't find anything I'll pull the lower intake.

Thanks again guys!