Rough idle

[jbstan]

It's finally cooler down here in Texas to do some work on my '82 Wag. Bear with me as this is a long post.

I recently had the Wag inspected and it failed because the idle was too high at around 1500rpm. I lowered it to pass, but the engine idles roughly and seems likely to stall when the idle is set below 1500rpm. If I have the idle low and start up the engine cold, it will stall and even stalls when coming to a stop without sufficient warm-up time. The engine runs great otherwise when driving around. My impression is the engine should be able to idle at ~600rpm without issues, so I suspect vacuum leaks and other issues.

The PO claims the engine was rebuilt, but the vacuum lines don't match the service manual. Diagram of the 82 vac lines below:



The smog stuff on the exhaust manifolds and the air pump are all gone. Vehicles older than 24 years old in Texas do not have to meet emissions as far as I know. The diagram below is what the vacuum lines on my Wag looks like right now at the moment.



I used a little vacuum pump to check for leaks and the charcoal canister purge holds vacuum so it is OK.

I found that the EGR doesn't hold vacuum so I pulled it out and could tell it's closed so it's not running stuck open at least. I'm able to move the pin up/down by pushing on the diaphragm. Though, the EGR doesn't hold vacuum nor does any vacuum action cause it to move at all so I think it's bad? Any suggestions on a source for a good inexpensive replacement?

I plan to fix the vacuum lines for the EGR by routing it through the dual CTO and the TVS, so the EGR doesn't activate when the engine is cold or it's cold outside. I tested the TVS with the vac pump and it allows vacuum to pass through freely when warm, and then I stuck it in a fridge for a while then did the vac test again and it is closed - the vac doesn't pass through as much so seems OK.

The VSD vac dump valve is long gone - do I need it? Service manual says it's for preventing the EGR from activating when manifold vacuum is low during hard acceleration.

Is there any difference in the 2 ported vacuum ports on the carb? The diagram shows a E and S port and the actual routing to EGR or distributor advance uses the opposite ports.

The 3-port side of the dual CTO valve seems leaky - the top port is supposed to be closed off when engine is cold but right now it doesn't hold vacuum. I think I'll need to replace it if I plan to use it again.

If I understand the service manual correctly about the two CTO valves for distributor advance, the advance receives manifold vacuum when engine temp is below 155F for faster warm up, or when engine is >220F to keep it cooler? "Modified" (ported) vacuum is applied when engine is between 155 and 220F. The nonlinear valve creates a modified vacuum that appears somewhere between ported and manifold when the load is light, so at idle the dist advance receives more vacuum than ported would provide.

Sorry this post is long, but I figure by giving a complete picture of the vacuum lines so I could get better guidance on what I should do about it. My goal is to replace all the vacuum hoses with new ones (suggestions for sources?), get a new EGR and find another dual CTO valve.

Would I have to readjust the timing after all the vacuum lines are redone?

Another thing I'm suspicious is not working is the fast idle cam because the engine doesn't really idle high when first turned on, it just tries to stay at the set idle point I have it on so I usually pump the gas pedal a little to keep the engine running as it warms up. How do I check this fast idle?

[FallonJeeper]

If you've checked all vacuum leaks and set the base timing and found nothing it's likely that you just need to adjust your carb.

With the original idle @ 1500, you were running in the "power circuit" of the carb. This means your idle mixture may have been out of adjustment and you would never know. Also, because you were idling so high, your fast idle for the choke wasn't being used as designed.

The first thing I would do, with the engine cold, is press the throttle all the way to the floor, to set the choke. This closes the butterfly and set's the fast idle cam. Check the butterfly, it should be cracked open about an 1/8th of an inch. Adjust as necessary. Start the engine and adjust the fast speed idle when the adjuster is sitting on the cam to the specified rpm. This will prevent it from stalling when the engine is not quite warmed up. That's it total pupose.

Second, once the engine is warmed up, I would press the throttle again to bring it off the fast idle cam. Now with the engine at the lower rpm, adjust the idle mixture/idle speed.

Re-check everything. FYI timing is a mechanical function related to engine speed. Adjusting the carb will not change timing unless the carb adjustment radically changed the engine rpm.

Wouldn't hurt to do a compression test either.

Now you should be all set. Good luck, hope this helps. If I missed something, I'm sure some of our fellow FSJ'ers will speak up.

[jbstan]

I took a look at the fast idle cam. Took a picture and annotated a few things here.



So first thing I noticed was there's a notch in the body of the bimetallic coil. The service manual mentions rotating the choke coil relative to this notch. When I first looked at it, the wire connector was on the left side and after I took off the whole thing I could see the fast idle cam action. With the gas pedal depressed all the way in once, the yellow plastic lever that holds the curb idle screw stays in place regardless of the choke actuator pulling in or not. When I start up the engine, the actuator pulls the choke all the way open. I suspected the bimetallic coil wasn't tensioning the lever enough so I rotated it so the wire connector lines up with the notch, but the choke actuator is still strong enough to pull the choke all the way open (about 3/8" from the back of the choke valve to the opening).

When I push the throttle a little, the yellow plastic lever drops down against the metal lever - that's the only time when the curb idle screw looks useful - and the engine idle drops. The choke valve never changes position and still remains wide open.

I'm thinking the problem is the choke actuator is not supposed to pull in all the way in when the engine is cold because I don't have enough tension on the bimetallic coil. Right now the coil is as if I took it off and then put it back in place without rotating it much at all. What's the proper adjustment for this?

EDIT: I found some notes on automatic choke adjustments here and on the 'net. So I pressed in the choke actuator and adjusted the screw on the back of it until the choke valve closes to about 3/16" between the back of the valve and the opening. Then I rotated the bimetallic coil to close the valve completely when cold.

Now it seems like the actuator will still pull in all the way anyway, so does the coil only resist the actuator action when temps are very cold? It's only in the low 80s here so I may not be seeing the full action of this coil. Now, the engine runs and doesn't seem to stall at all, and the dashpot solenoid for the throttle is all the way off the throttle lever and engine is idling a little high. I don't have a tachometer, but I'm guessing it's around 1200-1500rpm. The curb idle screw doesn't appear to have any effect on the idle. Also exhaust smells very gassy so I'm thinking the idle mix is way off now. Could it be that the idle mix was incorrectly set to provide more gas due to the choke valve being wider open initially?

I've never done a carb rebuild, tweaks, or adjustments before so I'm afraid to touch the idle mix screws without a lot of guidance. This Wag is the first project car I've ever worked on.

[tgreese]

Is the "S" connection on the carb ported or manifold vacuum? You need ported vacuum. If it's manifold vacuum, the EGR will be open at idle, which will give you a rough idle. One function of the missing 5-way CTO is to disable the EGR entirely while the engine is warming up. This improves cold-start performance significantly.

The EGR can also cause a rough idle if the pintle is dirty. Take the valve off and wire brush the working end. You'll need a new gasket.

Curb idle adjustment is on the throttle linkage, on the opposite side of the carb. When the engine is warmed up, the choke side of the linkage should do nothing. There is excellent information about the carburetor and adjusting the choke in the FSM.

[hockeydad]

out of curiosity, what will happen if you disconnect the EGR altogether? I have mine blocked off, because I am trying to get it to idle properly, and then I will worry about it at a later date. Dumb question, but was that wrong??

[jbstan]

I found an article on rebuilding the Motorcraft 2150 carburator and read the information on the fast idle cam and the mix adjustments.

After I adjusted the choke actuator to close the choke valve 3/16" as described by that article, the idle was really high. So I decided to carefully mark the positioning of the mix screws and then proceed to screw them in to find the maximum lean setting and turns out they were already nearly all the way in. So I backed both screws out about 1.5 turns and the idle came down to a reasonable amount. I don't have a tachometer on hand and need to get one, but my rough guess is it's still a little high. But the engine sure does idle very smoothly compared to before so I'm quite pleased. Manifold vacuum is about 14-15inHg steady. I have the EGR disconnected completely but otherwise am still using the original vacuum line setup that I intend to revert back to stock.

I took the Wag for a short drive around town, drives very smoothly and has good acceleration. It also doesn't smell gassy after I park it in the garage.

What's the typical RPM with both screws out about 1.5 turns? Right now the curb idle and dashpot solenoid are set to their minimums.

[tgreese]

The mixture screws are not supposed to affect the idle speed. You can stall the motor if you make the idle mixture too lean, but above that point, they should have little effect on the speed.

If you can't slow the engine to a stall by running the curb idle screw out all the way, then your linkage is hung up on on something else. Check that the choke fast idle stop is not holding the throttle open. If you have an idle stop solenoid, that is intended to hold idle speed when energized, and close the throttle to stall when the key is off. If both those check out ok, check that the throttle linkage is not holding the throttle open. You should be able to unsnap the throttle cable from the carb and not affect the idle speed.

[Rich88]

out of curiosity, what will happen if you disconnect the EGR altogether? I have mine blocked off, because I am trying to get it to idle properly, and then I will worry about it at a later date. Dumb question, but was that wrong??

Without properly operating EGR you'll get higher temps and possible pinging.

Read this: http://en.wikipedia.org/wiki/Exhaust_gas_recirculation

[FallonJeeper]

To adjust the idle mixture, with the engine warmed up, you first set the idle to about 850, that way you know you're adjusting in the idle circuit. Back the mixtures screws out a turn or two, until there is no change in the RPM. Then 1 at a time, turn the mixture screw in until you get a 100 RPM drop, and back off the mixture screw 1/4 turn. Repeat for the other idle mixture screw. While it's true that you don't use the mixture screws to adjust the idle speed. The mixture screws, if screwed in, and too lean, can effect your idle speed.

Once your mixture is set. Turn the screws in, again, one at a time and write the number down for each side. Ideally, you want them to be the same and balanced Once you have the numbers, turn out the screws the same number that you wrote down and re-check. Once you have them close to balanced, adjust your idle RPM to specs.

There is another way to do the idle mixture, which involves a vacuum gauge. There are plenty of articles and videos on the internethttp://www.youtube.com/watch?v=Rg8XH...eature=related on how to do all this. If you learn how to do this, and do it one time, you'll be an expert and will have learned a valuable life long skill.