Author Topic: Chasing my Idle (Read 10615 times)

awolff280sl · « **on:** May 07, 2014, 13:26:29 »

My car has a recurrent problem of maintaining a stable idle rpm that happens after it has been properly adjusted and appears stable, but only for a few weeks.
For example, I recently did a full tune up with new oil, plugs, filters, etc. I used an AFR to adjust the idle (as well as checking the mid-range/high range under load).
I adjusted the idle only after giving the car a good work out. The WRD is working fine. The car runs great, and the idle remained good, but only for a few weeks.
Over a period of a few weeks, the idle has become lower and lower, so much so that it is on the verge of stalling. It is not related to driving style, distance, speeds, etc. It may be weather/temperature related since it is getting hotter and more humid here.
This problem has happened several times in the past, and I have compensated for it by readjusting the idle. Once readjusted, it will stay stable for a few weeks or months until it needs to be readjusted again. Sometimes after readjustment it will then intermittently idle too high.
Is this unusual? If not, how do others deal with it?

stickandrudderman · « **Reply #1 on:** May 07, 2014, 16:47:08 »

Leave your AFR in and it will tell you a lot about why the idle is slowing down.

Cees Klumper · « **Reply #2 on:** May 07, 2014, 17:59:11 »

It sounds very unusual to me. One clue could be - is the required adjustment always the same / similar? (Ie always need to increase air, or decrease it, or what have you)? If so, then that would point us in some direction.

franjo_66 · « **Reply #3 on:** May 07, 2014, 22:10:50 »

You may have a faulty Constant Speed Solnoid?

I have experienced the same symptoms. Rebuilt injector pump, linkage adjustments, tune-up, new 123 distributor, new coil, etc
Car would run great but then after a few weeks, idle revs would drop, sometimes when I came to a quick stop, the engine would stall

Rechecked everything until we looked at the CSS. Tested it out and noticed that it was not working consistentlty
So just recently bought a good second hand unit and will be putting it in within next few weeks

Worth checking !

garymand · « **Reply #4 on:** May 07, 2014, 23:31:41 »

Not a bad idea, You can just look at the device and visually see where the butterfly. If you can't see it or push it and be sure, I would split the linkage and varify its the air side or fuel side.

awolff280sl · « **Reply #5 on:** May 08, 2014, 00:01:47 »

Thanks to all for the ideas. I have a 4 speed so it's not the CSS.
I will check the AFR now at low idle and take note of what is out of balance and report back.

ja17 · « **Reply #6 on:** May 08, 2014, 06:12:12 »

Hello Andy,

Check your ignition point dwell reading right after the tune up then when the problem begins. Your ignition points may be "settling in" or closing which changes the dwell and the ignition timing thus lowering the idle as the timing becomes a bit more retarded. It is not un-common for new ignition points to "settle in". Worn or rough rubbing cams on the distributor or failing to add distributor lube to the cams can accelerate wear of the rubbing block on the points causing the points to close and the ignition to become more retarded. If you set the ignition points with a dwell meter during the tune-up, check the dwell now.

awolff280sl · « **Reply #7 on:** May 08, 2014, 11:49:28 »

Thanks Joe, but I have a 123 distributor in there just to try to avoid what you mentioned.

Larry & Norma · « **Reply #8 on:** May 08, 2014, 13:05:46 »

AFR? What's that some sort of CO measuring device

awolff280sl · « **Reply #9 on:** May 08, 2014, 14:16:46 »

ok. I ran the car around with the AFR hooked up.
At idle, the AFR was 16.5-17.0 and rpms about 100. This is quite a change from a few weeks ago where the AFR was 14 and the car maintained 850rpms over several weeks until recently.
Re-adjustment required 4 CW clicks on the FIP and about a turn and a half CCW of the idle air screw. AFR is now 13.9 and rpms 850 at idle. There is a obvious "hiss" at the idle air screw.
I cannot account for this need to readjust. I will report back if things change again.

Larry: AFR is AIR/FUEL ratio. Ideal at idle or cruise is about 14.1:1 See here: http://www.innovatemotorsports.com/products/lm2.php

stickandrudderman · « **Reply #10 on:** May 08, 2014, 17:11:36 »

Interesting observations.
Personally I would have split the linkage and added 1/2 a turn of length to the throttle rod since it appears that your mixture is getting richer.
I have seen a similar phenomenon where the car would idle perfectly but the AFR would change as soon as I put it in gear (auto) and it was play in the ball joints of the throttle mechanism that was allowing the CSS to open the throttle butterfly slightly before opening the rack hence the mixture change.
I realise that you have manual but still worth a look.

awolff280sl · « **Reply #11 on:** May 08, 2014, 18:40:07 »

Stick,
My linkage is very tight, no slop.
I was thinking that I could lengthen the throttle rod as you said, and I will try this next if the idle starts to drift again.

stickandrudderman · « **Reply #12 on:** May 08, 2014, 20:19:58 »

Actually, having re-read your post your fuel mix is getting weaker, not richer, but the advice remains almost the same!

awolff280sl · « **Reply #13 on:** May 11, 2014, 12:35:24 »

Follow-up on my idle issue, I still cannot find the cause, but what is happening is now reproducible.
After re-adjusting the idle, the problem recurred. I started from scratch by redoing the engine linkage. I followed Joe's tutorial, and I did make some minor adjustments to the all of the rods. I then readjusted the idle.
This is what is happening: The idle stays good while drying around town at relatively low speeds. However, after coming off of the highway, the idle drops to about 400-500. BUT THEN, if I tap the gas pedal the idle goes up to 850 and will remain stable as long as I do not rev too much. This sequence is reproducible.
This sounds to me like the linkage is "hanging up" somewhere but I cannot find where. If I push on various spots on the linkage while the car idles at 850, I cannot get it to drop to 400-500.
The throttle and pump rods are on their stops. The throttle dampner is not holding anything up, nor is the solenoid for the AC. The progressive linkage roller is in the right spot. Nothing is bent, everything moves freely. The linkage pivots are lubricated.

Cees Klumper · « **Reply #14 on:** May 11, 2014, 14:44:28 »

Air venturi flap on the intake manifold hanging up?

Otherwise sounds like you have the usual suspects covered.

Oh, what about the distributor - advance mechanism / flyweights getting hung up? Changing the ignition timing has a big impact on the idle RPM as well.

stickandrudderman · « **Reply #15 on:** May 12, 2014, 17:11:34 »

Is the return spring fitted at the butterfly and if so is it the right one?
To test for this you would simply push the bellcrank at the butterfly towards the closed position. If it slows the idle down then you have found your problem.

garymand · « **Reply #16 on:** May 12, 2014, 18:10:26 »

I agree. You will have to locate the culpret and the mechanical advance could be it. I'm thinking you could pull the vacuum hose to the distributor and reconnect. That may not change the weights, but it should repeat and check the vacuum advance.

I've had binding of the weight/spring/point cam lobes that you can only fix by pulling the cam and cleaning and re-oiling the shaft. That is what the felt oil sponge is for in the center of the cam under the rotor:keeps oil in and moisture out. If it is the cam, just by manually rotating the rotor, you can force the weights out against the springs and possibly feel a frictional hangup. I make it a habit to do this now after finding this problem on 3 or 4 distributors. Pull the cap, grab the rotor, rotate to stops in both directions. The start and stop should be mechanically smooth and repeat perfedtly. It should be a smooth transition as the cam engages and then pushes the weights out. Then when you release your force, the rotor needs to come back freely under spring pressure to exactly where it started. no farther, no less.

Maybe too, the FIP rod is not freely coming back to idle position.

awolff280sl · « **Reply #17 on:** May 12, 2014, 21:57:43 »

Thanks to all for the input.
I am using a 123 distributor, so I do not think that the mechanical advance is involved.
The throttle butterfly return spring is correct, and the butterfly appears to be fully closed to air at idle in all cases.
The FIP rod is not hanging up, but I am curious about the setup of the length of this rod. I used the alignment hole on the bracket attached to the intake manifold, so that the ball head at the intake manifold end is dead center in the middle of the alignment hole. (Interestingly enough, the distance from the ball on the FIP to the ball on the control arm measured 233mm). HOWEVER, the FIP is not quite on its idle stop with the FIP rod connected. Not sure if this is important.
Anyway, I have to ride around a few more times and see if I can spot something under the hood when the idle drops. And maybe the AFR can tell me something at that point as well.

garymand · « **Reply #18 on:** May 12, 2014, 22:16:32 »

No no, sorry, not the external FIP rod, the FIP rack internal to the FIP.
1) FIP has to be at it stop. readjust the other rods. Both the throttle and the fip start movement from on their stops. As you open the throttle with the short rod, both the throttle and the fip should just open at the very same time (in sinc)
2) Have you looked at the bottom of your oil cap yet?
3) Did you try rotating the rotor shaft on your 123?

awolff280sl · « **Reply #19 on:** May 12, 2014, 22:42:16 »

Gary
1) Because the length of the FIP rod is adjusted so as to make the ball head perfectly aligned with the alignment hole (on the manifold), I would have to (slightly) rotate the arm on the end of the cross rod to get the FIP to rest on its stop. There is a small Allen screw in the arm, but I do not know if the position of this arm is adjustable.
2) bottom of my oil cap on the valve cover?
3) my timing is is dead on.

Cees Klumper · « **Reply #20 on:** May 13, 2014, 04:48:18 »

Also the 123 distributors need the vacuum line input to effectuate advance. I don't know how it converts the vacuum from the engine to the actual afvance, but it's possible / likely there's a mechanical step in there. Maybe not likely the culprit, but still possible I think.

garymand · « **Reply #21 on:** May 13, 2014, 22:38:41 »

OK, lets backup a little, there are some basics missing:

You don't turn just one ball head at a time, they didn't design it that way. The rod ends are threaded in opposite directions so you loosen both locknuts, one on each head, and turn the rod, not ahead.

Careful about back lash, this is tricky, the gas pedal pushes a rod that eventually results in pushing the throttle off its stop. My point is, there is no backlash and all the balls and heads are pushing the throttle against it spring. When you backup the throttle, the spring presses back. that's no backlash. This is critical because you have a split throttle that must be sync'd mechanically. As the pedal takes up the slack and starts the throttle off its screw (do you know how the screw is set?) the FIP should be exactly lifting off it stop at the same time. And the springs should bring them back to stop at the same time as you back off the pedal. Never push one side or the other expecting both to move in sync, they will not, no matter how tight your ball & sockets are. This is to ensure you linkage is not at fault. (but I have ignored the throttle valuum pot and the electric idle solenoid. you must adjust them too, if you have them.)

Once you get the linkage set we can go on to the FIP Rack, spark timing that is controlled by your 123, and where the water is coming from.

1) When I 1st said ROD, a few messages ago, I ment to say RACK. The rack is inside the FIP. It needs to slide smoothly forward in the FIP with the throttle, but it is lightly spring loaded and must come back on its own all the way to stop. It might be sticking. I thought you might read the manual on how to push the rack back and forth to ensure your FIP is not at fault.

2) sorry about the oil cap. i got your problem confused with another.
3) We are talking about how well your distributor repeats mechanically. If the mechanicals inside the distributor come back to the right place at idle.

awolff280sl · « **Reply #22 on:** May 13, 2014, 23:41:21 »

Gary, thanks for taking the time with your explanation. I re-adjusted my linkage from scratch, including the dashpot, AC solenoid, and accelerator rod off the side of the engine block.
I must have missed something having done it piecemeal before, because now the FIP is at its stop with the alignment through the hole dead on, throttle butterfly set just right, and both throttle and FIP coming off their stops simultaneously. My idle AFR/rpm was then somewhat off and had to be readjusted.
My idle is now much more stable at 850. So far, the rpms only drop (to 600) when turning the wheels (I have PS) while moving at very slow speed. While I realize that this is normal, the rpms do not come back up on their own. The rpms then do come back to 850 (and stay there) after revving the engine a bit. I can live with this.
Thanks to all for your help.

ja17 · « **Reply #23 on:** May 15, 2014, 12:39:00 »

Andy, make sure the pivot on the engine block moves freely. These tend to be the first thing to corrode and bind.

awolff280sl · « **Reply #24 on:** May 15, 2014, 13:06:38 »

Yes Joe, thanks.
Everything is working very well now.
Question: is the roller in the progressive linkage something that needs replacing at times?

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Author Topic: Chasing my Idle (Read 10615 times)