Rough idle

[alec_b]

So ever since I got the regal the idle has always been just a touch away from smooth. Once in a while it'll be perfect, but more often than not it feels almost like the lope of the camshaft when you're sitting in the car, if that makes sense.

 

I've done a complete tune-up on it with good parts, copper plugs and a good Belden wire set. Fuel filter is new, air filter is new. I was tinkering with it tonight and I found that unplugging #6 (I think, looking at the motor it was the front right injector, so maybe #5) didn't effect the idle at all. But anything off idle it would make the motor miss, which it doesn't ever do off-idle.

 

Seems like maybe poor injector flow at idle? Or should I do a compression test? I've hooked up a vacuum gauge to it at idle while it's acting up and it hold a dead steady 15 in/lb. If I'm not mistaken the needle should shake if I've got say a burnt valve right?

 

I'm going to try and look into it tomorrow but I doubt I'll have time. I want to pull a plug and see if that might help narrow it down.

[91GPLQ1]

Most likely one or more bad injektor?

Lift Upper intake manifold, unplugg the electrical connectors from injektors an measure the ohm´s over the pins.

Resistance should be within a few tens of ohms at all injektors.

[mfewtrail]

There are some TSB's for 3800's regarding clogged/partially clogged fuel injectors. I don't know if the TSB specifically applies to your year, but that's always a possibility. Rough idle, chuggle, misfires, etc. can be caused by a problem like that.

[Jssuper]

It does sound like a partially blocked injector to me too. Seafoam..? I'd prolly try that before harder labor.. My luck is such that more often than not the easy fix doesn't work.

 

Its probably worth a shot though

Edited December 12, 2010 by Jssuper

[Galaxie500XL]

What's bothering me is the steady vacuum readings. Misfires usually show as fluctuating vacuum. Wasn't there an issue with some of the 3.8's with harmonic balancers that went bad, because the rubber debonded? That would definitely cause some interesting vibration issues.

[mra32]

Sounds similar to my issue. Which I have partially documented my progress in a thread I made in the powertrain section. Ive checked or every single sensor that I know of with the exception of the knock sensor and the CPS. I've replaced dubious spark plug wires, set the correct gap on the spark plugs, checked compression on all cylinders, measured vacuum, everything is fine. I know that I should replace the ICM and coil packs, but I've had less and less time to do some diagnostic work on my car. I think whenever I get a free couple hours, I'll pull the plenum and check the injectors. I think i might have one that is a little messed up.

 

An interesting factiod: My car sat from friday afternoon till monday afternoon and started in 1 crank, like it used to, but when I go to start it after like 4-12 hour periods of sitting, it takes a few cranks. Im thinking maybe an injector is dumping fuel in one cylinder, hence the poor mileage and rougher idle.

[alec_b]

If my car sits overnight it starts on the first crank, even in freezing cold. It also starts right away on hot restarts. Anything other than that and it takes a few cranks for it to fire and it coughs just a little bit once in a while. That will happen after about 1 hour of sitting until the next day then it starts right up again.

 

Oh and the balancer is brand new.