Help with rough idle while in gear

[dbuie]

She idles near-perfect until you put her in drive or reverse. Then she idles rough. No amount of playing with the timing, mixture, or idle screw seems to make a difference. I even cranked the idle screw way up and as soon as I put her into gear it's back to rough idling. I checked all vacuum lines this morning and did discover one that had been damaged by a ground wire mount. I fixed this and no affect. What could be causing this?

Thanks.

[brad_fsj10]

Engine should Idle at 500 with stop solenoid disengaged (unplugged) and at 600 with the solenoid engaged (plugged in). Adjust the carb with engine warm, solenoid engaged (extended), and EGR, air pump diverter, and CAP plugged.

After that, when it idles smooth in gear, start plugging things back in to find a leak. I suspect your EGR valve may be leaking due to vacuum at idle. EGR Should be ported vacuum, not manifold.

[tgreese]

Not sure about the '89, but the earlier models of EGR valve are very sensitive to carbon buildup. The carbon buildup will hold the valve open and cause a rough idel (the valve should be closed at idle). The fix was to pull the valve and wire brush the pintle (the part that sticks out and blocks the exhaust flow when cold). You'll need a new gasket.

The '89 has some extra stuff in the EGR circuit that I am not familiar with, but the EGR carbon problem may still apply.

[dbuie]

OK, I will check this. Thanks.

[dbuie]

No dice. Even bypassing the EGR (by plugging vacuum line) it still idles rough. And now it does it even when not in gear. Yesterday she ran perfect even with temps in the 30's. Could it be ignition-related? I recently replaced the cap, rotor, and plugs. I haven't replaced the wires yet and I have no idea how old mine are. Could it be the ignition box or pickup in the distributor?

[brad_fsj10]

Check for fuel dripping through venturies at idle... search on verturi for the fix (new gaskets, and opening up circuit).

[tgreese]

No dice. Even bypassing the EGR (by plugging vacuum line) it still idles rough. And now it does it even when not in gear. Yesterday she ran perfect even with temps in the 30's. Could it be ignition-related? I recently replaced the cap, rotor, and plugs. I haven't replaced the wires yet and I have no idea how old mine are. Could it be the ignition box or pickup in the distributor?

Disconnecting the vacuum line won't make any difference if the valve is stuck open. You have to remove the valve from the top of the manifold, clean off the carbon on the interior part, and put it back. Nothing else will make a difference, if carbon build-up is the problem.

Another possibility is the ignition wires. Bad wires will behave differently depending on the humidity. If the weather was different yesterday, the wires may be at fault.

[dbuie]

[quote=tgreese]Disconnecting the vacuum line won't make any difference if the valve is stuck open.


How right you are. I will try this as soon as I can but with it getting dark at 5:30 it may be a while. Thanks for giving me a refresher course.

[dbuie]

Check for fuel dripping through venturies at idle... search on verturi for the fix (new gaskets, and opening up circuit).

Brad, I think that I'm going to take her to a carb guru here locally and have it rebuilt. I can smell fuel and the exhaust smells like pure gas anyway. Of course it did this before she started running rough but I will report back with an update as soon as I have one. Thanks.

[dbuie]

Update-Fixed

Tonight I decided to bypass my HDC CTO and NLV and used a diagram that someone had posted here before that used a simplified vacuum setup. This setup uses ported vacuum to the distributor and the Spark CTO. It definitely cleans up the front of the manifold. I also tested my purge valve on top of the charcoal canister and it held vacuum.

Well, after doing all of this I fired her up and she now idles smooth as silk, even when I put her in gear. Must have had a vacuum leak somewhere is all I can figure. I am still going to have my carb rebuilt by a local carb guru since she runs too rich. The idle mixture screws don't seem to make much difference and I've read here that the power valve could be dumping too much fuel.

Thanks to all who replied.