I'm not a newb at this or anything, but I have a slight stumble in my idle that I cannot pin down. Fuel pressure is normal, timing is set correctly, I'm pretty sure there are no vacuum leaks, TPS is set right, the O2 is new, and I just cleaned the IAC and throttle body. The only thing I can think of is that I picked up a set of used injectors from someone who claimed they were 19#/hr injectors from a GTA with a 350. If they are indeed 19# injectors I can see the problem (mine should be 22# stock), but I thought that all 350's came with 22's. Anyways, can anyone think of anything else to do before I go out and buy some new injectors?

EDIT: I forgot to mention this but the coil, cap, rotor, wires, and plugs are all less than a year old. I did go through a few months with some serious fuel problems(Bad fuel pump and injectors) so maybe the plugs are no longer good. I'll check them next I guess.

 

The plugs show some signs of aging, but are not bad enough to cause a stumble at idle. Compression is good and I did both the carb cleaner at the intake seams trick and the listen with a hose trick to check for vacuum leaks both turning up nothing. Is there something I'm missing or should I order those new injectors now?

 

I kinda feel like I'm talking to myself here, but I used seafoam and got no improvement on the idle. Any suggestions?

 

Did you adjust the minimum air rate after cleanng the IAC?

 

I didn't think that would effect the stability of the idle, but I'll do it anyway for the hell of it. I'll readjust the TPS while I'm at it of course.

 

Without the IAC connected, my idle moves between 400 and 600 RPM and even stalled once. Trying to set the minimum idle RPM under these conditions is impossible. The stumble in the idle does not seem to be attached to any individual cylinder so I think my air fuel ratio is off. We'll see.

 

Check your MAP sensor as it could be carboned up, as a speed density car needs a good reading. Also check your EGR valve and vaccume lines for the same issues.

If they are 19lb injectors it will run a little lean at idle and very lean up top. None of these will cause a bad idle unless its very cold out.

Just some more insight

Faded

 

I'll try cleaning the MAP sensor tomarrow. As for the EGR, the hose broke and I subsequently plugged the vacuum line for now. Unless it is stuck open or the vacuum from the line holds it closed, I don't think thats the problem. I'll probably clean the EGR and fix the vacuum line to it anyway when I get some time.

 

I cleaned the MAP with carb cleaner and it dramatically increased the throttle response, but had no affect on the idle quality. I'll probably remove the plenum to clean the EGR and fix the hose and I'll clean everything out and relocate the MAT sensor while I'm at it.

 

you may have a very slight vacuum leak. even a small one can cause a slight hesistation at idle. i know my runner gaskets and my exhaust manifold gaskets are leaking but my car still idles almost perfect.