3.8 running rough only at idle

[johnson350]

Hey guys, I'm having a problem with the 3.8 in my 84 Regal. Motor is running with CCC. Has all compnents except I removed the EFE grid under the carb.
The car ran fine yesterday. This morning whenever I fired it up, I let it warm up till the choke came off, then it wouldn't idle worth a crap. It has no lack of power while accelerating, doesnt sputter or anything while accelerating like it always has been. It only stumbles over itself at idle and will die if I don't keep on the gas. Had to double pedal it at stop lights on my way to work today.

Could this be an EGR problem or something to do with the timing? I'm not sure, tell me what you guys think.

 

[joesregalproject]

3.8s can be finicky but it's usually small stuff. Take the path of least resistance first. Try cleaning out you PCV valve in some gasoline first. See if that helps.

 

[Peter]

id put my money on there being a vacuum leak somewhere, check around the base of the carb and all the lines

 

[johnson350]

Agreed joe, they can be finnicky motors. It was rebuilt about 40k ago and had some better internals put in for more power and durability and this is the only time it has ever acted up.

Just like you said, I'll go through it all this afternoon when I get home. And I'll be sure to check the many vacuum lines. It's time for maintenance anyway. Just hope the problem is not expensive 8)

 

[johnson350]

Ok so I checked it all out last night. First thing I checked was the spark coming from the distributor. All have good spark Except for #4. Its getting spark, but only about half the time, and its really weak when its getting it. Gonna pull the distributor cap this weekend and find out whats going on under there.
I've been having a very slight misfire too for about a month, it was almost nonexistent, could barely feel it. Guess its getting worse.

 

[johnson350]

So I pulled the cap off and everything looked ok. I cleaned up the contacts with some emery paper, checked the wires with an ohms meter (and they were fine), changed the rotor because the old one looked pretty worn, and changed all the spark plugs. Nothing changed except you can feel the miss even more. It seems like it may be getting worse.
Keep in mind this is only happening at idle. Its fine above idle, no miss. Also its only happening on cylinder #4. All the others run fine. That's why I believe it is an ignition problem.
Could it possibly be the ignition module starting to fail?

 

[King_V]

Only cylinder #4?

WARNING: I am NOT an expert by ANY means . .

But, that said, could it be a hydraulic lifter that's starting to fail? Like, perhaps it's leaking out a little, and it behaves as "collapsed" only at idle, but once it picks up speed, it's holding enough oil for the car to run normally?

Just a guess...

 

[johnson350]

I'm gonna say it's probably not that due to the fact that the engine was rebuilt about 40k ago. The motor doesn't make any strange noises at all, sounds normal. It had a high volume oil pump put in with the rebuild, so I know it's getting oil. It doesn't feel like anything mechanical failing, idk. :?

 

[jetsetw31]

So I pulled the cap off and everything looked ok. I cleaned up the contacts with some emery paper, checked the wires with an ohms meter (and they were fine), changed the rotor because the old one looked pretty worn, and changed all the spark plugs. Nothing changed except you can feel the miss even more. It seems like it may be getting worse.
Keep in mind this is only happening at idle. Its fine above idle, no miss. Also its only happening on cylinder #4. All the others run fine. That's why I believe it is an ignition problem.
Could it possibly be the ignition module starting to fail?

The problem your describing "Miss only at idle" sounds more like a fuel problem in the carb or a vacuum problem. I say that because Your problem is a "sometimes" issue (only at idle). When the ignition has a miss, it does not go away. That miss is there through the whole rpm range not just part of it. Also the module usually goes bad when heated and it shuts the ignition down completely every time the module gets hot. Same goes for the pick up coil.
But since your say the number 4 cylinder is missing, Maybe your not feeling the miss that much at speed.
How did you test the cylinders? How old are the wires?

It may be the wires. Even though you tested the wires you could have gotten a false reading on them. Discoloration in the wires is a tell tale of a bad wire. If you test it away from the other wires it may test the same because it's not resting up against any metal to make it arch. Also a ohm meter puts out a small current that won't go through the worn insulation. It'll detect a broken insulation though. I'd go through the wires again.
Now if the wires are new and the cap does not have a crack in it or carbon tracks. It's not an ignition issue. Your back to the air /fuel.
Also Mechanical issues are not sometimes either. A lifter fails it stays that way until replaced.
T

 

[King_V]

I'm gonna say it's probably not that due to the fact that the engine was rebuilt about 40k ago. The motor doesn't make any strange noises at all, sounds normal. It had a high volume oil pump put in with the rebuild, so I know it's getting oil. It doesn't feel like anything mechanical failing, idk. :?

I'd agree . . though I suppose that, with crappy luck, you could've gotten a new lifter that was semi-defective or marginal when it was new. Long shot, I'll admit. I was thinking along those lines because your investigation indicates that it's only a problem with cylinder #4.

It may be the wires. Even though you tested the wires you could have gotten a false reading on them.

Now that this was mentioned, I'd pursue this first . . can you swap the ignition wire with one on another cylinder? If the problem "moves" to the other cylinder whose wire you swapped with #4, then it's a bad wire.

If only #4 is still an issue, it's not an ignition wire. . . and . . uh . . more digging is required. 🙁