86, 5.0L, AOD, 177K miles. This "problem has been slowly getting worse over the past few months. After coming off the freeway, sitting at the off-ramp light, it starts to shudder. Like it's got a somewhat lumpy cam. If I shift into "N" it idle surges up around 8-900 then settles right back to 600. Shift back into gear and it drops to 500 rpm and starts shuddering again. I strongly suspect a bad injector(s). I just had the codes pulled and there were none. But i guess it could be a simple as bad gas. Ethanol blend on the last tank. I'm ready for another fill-up so I think I will go for name brand mid grade and maybe drop in either octane boost(?) of some sort of injector cleaner. The last cleaner I ran thru was Lucas brand. Could my plug wires be crossed incorrectly? New wires just over a year ago (Nov), same with the plugs. I have advanced the timing to 14 degrees BTDC and opened the gap to .0054. Related? Thanks in advance.

p.s. I did do a search but most "shudder" problems were at higher speeds/rpms.
At freeway speeds or just cruising around town, it runs fine.

 

If your idle is glass smooth when you take it out of gear, your plug wires are not crossed, you'd have some very evident signs if they were. I'd bleed the system and change the fuel filter first, just as a precaution, I'm not sure it is affecting your idle shudder. If it has been awhile since you've done it, I would change the filter anyway. When you put on new wires and plugs did you change the cap and rotor. With the high energy ignition systems you get an awful lot of spark generated there. I'd take a look under the cap and check for carbon tracing which can lead to an electrical path other than normal. I just changed my cap/rotor today as the mileage called for it in my over-compensating preventive maintenance. I keep the last cap/rotor as a spare and discard the oldest one on hand. Cost was all of $14.75. The IAC may be affecting the idle. Have you ever cleaned it? If not it's not complicated and may help your issue. If you have a Haynes or Chilton Manual you can see what it looks like. Take it off and use carb cleaner in the two ports and clean out the gunk. Try this for a starter. Good luck.

 

New cap/rotor when I put the new plugs/wires in(Nov.03). I changed the fuel filter last summer. I also cleaned the IAC last summer and put in new TPS last weekend. It does idle smooth when not in gear, but after several minutes(ten or so), it acts like a lumpy cam. The new motor, to the best of my knowledge(assumption) has a stock cam.

 

Kinda sounds like its suckin air from somewere check vac. lines.
You said its ok in N just acts up when in gear ?
Do a compression check you might be losing a ext.valve.
Wouldnt surprise me at 177k.
Also read your plugs when you check compression check.

 

MinnMan, Its only 177k on the tranny. I put in a reman'd motor in Nov 03. The egr is suspicious. My poking around with the stethescope indicates some minor leaking where it mounts to the TB. From what I've checked vacuum lines wise though, is that all are ok.

 

Charger Fan,
Sounds like you're on the right track then. Once you check your EGR I have a feeling that you'll gat a handle on this. Have you checked for a vacuum leak yet. I kinda doubt it has one or it would be idling irregularly.

 

Today, new fuel filter, air filter, breather filter, cap/rotor, and full tank with 10 oz. of Lucas fuel system treatment. I guess I'll see in the morning when I get off the freeway if anything has changed.