A10 510 engine surging in neutral

[IsaacHeink]

Hey all, my car's engine is surging to 2,500 RPM when I put it in neutral, then idling at 2,000 after the initial surge. Ordinarily, my car idles between 1,100 and 1,500 (high, I know). Does anyone have any ideas what the problem could be? I replaced the fuel filter on October 1st, and it is currently at 239060 and is due for an oil change at 239090, which will happen this weekend, come hell or high water. 

I've done some reading on here and in my Haynes manual, and it seems like this is a fuel system issue, likely a carburetor? Does that sound right?

Thanks in advance.

Edited November 8, 2019 by IsaacHeink

[datzenmike]

Idle is way too high. Have you turned the idle speed screw down? Try that first.

 

Take the top off the air filter when the engine is warmed up and look. Is the choke fully vertical and open??? If not the fast idle cam will probably be on as well. Choke plat must be vertical to be off.

 

Next is a stuck fast idle cam. Choke may be off but fast idle cam is stuck, Try spraying all the linkages with WD-40. Hold throttle half open and work the choke plate open and closed. The fast idle cam looks like this...

 

 

Make sure it's free to move.

 

Last...

 

Find the BCDD. It looks like this...  It may be too sensitive and not shutting off after a deceleration.

 

The round thing at the top with the 6 screws and the small rubber plug in the middle. Pull the rubber plug out and turn the screw inside counter clockwise one or two turns. Keep track in case this doesn't help and you can put it back. Counter clockwise lowers the sensitivity of the BCDD and keeps it from staying on.

[IsaacHeink]

43 minutes ago, datzenmike said:

Idle is way too high. Have you turned the idle speed screw down? Try that first.

 

Take the top off the air filter when the engine is warmed up and look. Is the choke fully vertical and open??? If not the fast idle cam will probably be on as well. Choke plat must be vertical to be off.

 

Next is a stuck fast idle cam. Choke may be off but fast idle cam is stuck, Try spraying all the linkages with WD-40. Hold throttle half open and work the choke plate open and closed. The fast idle cam looks like this...

 

 

Make sure it's free to move.

 

Last...

 

Find the BCDD. It looks like this...  It may be too sensitive and not shutting off after a deceleration.

 

The round thing at the top with the 6 screws and the small rubber plug in the middle. Pull the rubber plug out and turn the screw inside counter clockwise one or two turns. Keep track in case this doesn't help and you can put it back. Counter clockwise lowers the sensitivity of the BCDD and keeps it from staying on.

Thanks so much! I'm excited to get some feedback and some stuff to try.

 

I haven't! To be honest, I haven't done much work on my car in the past. I do the easy stuff (oil changes, radiator care, fluid levels, fuse changes), but have never worked on my car in any real capacity because I am scared I'll mess something up. I've always wanted to learn, so I'm starting now. I have the perfect tool (a workable car with some issues) to learn. Anyway, I will try adjusting the idle first thing on Saturday after I change my oil! Is it odd to you that it is only starting to surge even though I've had the idle so high for so long?

 

Truthfully, I'll have to do some reading about the choke and fast idle cam to understand their function and location before I mess with them, but I'll do that tomorrow night so I can check on them Saturday. 

 

I'll try lowering the sensitivity to the BCDD as well. Should I do this while my car is idling and listen for changes in the idle? 

[datzenmike]

The BCDD is set by a sudden deceleration from high rpms. It opens a small 'carburetor within the carburetor' and allows a small amount of gas and air in to prevent a severe lean condition while slowing down. This will burn properly and not just go out the exhaust as unburned hydrocarbons. When the vacuum level returns to normal it should close and reset but it can stick giving a fast idle.

 

One thing I forgot is the surging. This can be a vacuum leak around the carb gasket on the intake manifold. A previous owner probably just turned the idle speed up so it would drive.

[scooter]

like mike just said, check for leaks. if you have any rubber hose nipples that are open or cracked vaccuum lines that could help cause this. get a 12mm wrench and make sure the carb is actually tight on the intake. from what i remember about the stock carbs a couple of the nuts are a little hard to get at but if they are finger tight that could definitley cause this. i have had them back off before to the point that i could just pick the carb up right off the motor.

[IsaacHeink]

Hey guys, I just changed my oil, warmed my car and inspected my choke, and it was totally vertical. Something I noticed when observing the car while I warmed the engine before changing my oil: It does idles at a stable 1300 rpm and runs smoothly, which made me realize, the surging and high idle only happens when I am driving it. 

Sorry to be such a novice, but how do I manipulate the throttle? And can you point in the direction of the idle speed screw?

 

[datzenmike]

Idle speed should be around 750-850.

 

See the Philips screw just to the left of the lower left corner of the red square? That is the idle speed adjusting screw.

 

On a warm engine, choke off, turn the idle speed screw down as low as it will go and still run. Now turn the other screw at the bottom center. This is the idle mixture screw and adds or removes idle fuel. Turn in or out slowly a 1/4 turn at a time, giving it a few seconds to register a change in idle. Adjust until you have the smoothest fast idle you can. I assume the idle is stronger now and has gone up, so turn the idle speed back down. Repeat the mixture adjustment. You'll have noticed there is about 1/2 or 3/4 of a turn where there is no change but idle quality drops off on either side? Just roughly set in the middle. Keep adjusting for the best running speed and keep turning the speed down until you are at around 800 RPM and you can't improve the idle quality any further. The idle speed is now correctly set.

[IsaacHeink]

I turned the idle speed screw down (counter-clockwise) and the idle speed never decreased. I turned it eight whole rotations until it felt like the screw was going to come out of it's fitting. Is this normal? To see no change like this? 

I don't know if this fact is consequential or not, but my engine does not shut-off right away when I turn the ignition off. It runs and shakes for up to 15 seconds after I remove my key.

[IsaacHeink]

I took the air filter body off so that I could check the fast idle cam, and it moved freely as I opened and closed the choke. The only thing I noticed was that when the choke was all the way open the cam wasn't all the way down, if that makes sense? Like there was some distance between the cam and the arm that moved it in accordance with the choke plate. 

After the air filter was off, I did make some troubling discoveries. 

First, the hose that runs from the air filter body the engine was severely cracked. I'm going to replace it before re-installing the air filter body.

Second, one of the nipples on the carb was "mucky" and cracked. I think this actually might be my problem, so I'm going to replace it and see if that helps. 

Lastly, I saw that some wires going into the manifold directly below the car are broken and disconnected? I don't know their function or how long they've been disconnected, but it was quite shocking to see them in such disarray. 

I've been taking pictures and I will post them later, but I am racing against the sun right now. 

[datzenmike]

The idle speed screw should allow the primary throttle plate to close completely. So air must begetting somewhere. Use a flashlight and look down the secondary barrel. It should be closed. I had an unexplained fast idle I couldn't adjust away and it was the secondary throttle plate stuck partly open. Try pushing it down with a pencil. Once closed the idle dropped and it worked after that.

 

Check the primary throttle plate for an obstruction that's holding it open.

[IsaacHeink]

47 minutes ago, datzenmike said:

The idle speed screw should allow the primary throttle plate to close completely. So air must begetting somewhere. Use a flashlight and look down the secondary barrel. It should be closed. I had an unexplained fast idle I couldn't adjust away and it was the secondary throttle plate stuck partly open. Try pushing it down with a pencil. Once closed the idle dropped and it worked after that.

 

Check the primary throttle plate for an obstruction that's holding it open.

The secondary throttle is closed but opens fine with some pressure. 

 

The primary plate is closed as well. 

 

I'm puzzled and stuck. Can you think of anything else?

[datzenmike]

 You're sure it's closed because no air = no running.

 

 

At the top, the thing with the 6 screws and the rubber plug in it. Pop the rubber plug off and turn the hidden screw inside counter clockwise a turn or so but keep track so it can be put back.

[IsaacHeink]

25 minutes ago, datzenmike said:

 You're sure it's closed because no air = no running.

 

 

At the top, the thing with the 6 screws and the rubber plug in it. Pop the rubber plug off and turn the hidden screw inside counter clockwise a turn or so but keep track so it can be put back.

If the secondary throttle is the plate inside the hole next to the whole with the choke, then yes, I'm sure it was closed. And I'm assuming the primary throttle is beneath the choke? That one was closed as well. However, I did not check these while the car was running. Should I start my car then check the primary and secondary throttle plates?

 

Oh yeah, I forgot to tell you about the BCDD! I found the BCDD on my car, but it doesn't have a rubber stopper, but actually has a hose running from it instead.

[datzenmike]

It isn't much that it has to be open to cause a fast idle. My carb had been sitting and there was a small amount of rust. Once pushed closed it cleared.

 

I haven't had that style apart. Carefully take the cover with the hose to it off and see if thee is an adjustment screw underneath.

[IsaacHeink]

I've been doing some reading in my service manual, and I think the cracked hose running from the air cleaner was running to the A.B. Valve, do you all think that could be causing my high idle? I've posed a picture of the cracked hose and a picture showing the valve its hose runs from. 

I went to Advance Auto and found some generic hose that seems like a good fit, however, the hose on the car has a metal piece inside of it that looks like a valve of some sort, and I'm not sure if I want to cut the original to get the valve out before I have a sure-fire replacement.

https://imgur.com/mFfxT73

https://imgur.com/eqjAbiZ

 

Also, Mike, here is the BCDD on my carb. I gave it a good look-over and I don't believe it has a adjustment screw. 

https://imgur.com/EioDJud

 

If I have any light tomorrow when I get home from work, I am going to re-check that my secondary throttle is completely closed. 

[datzenmike]

 

Pull the hose off and plug the hose end see what happens. I guess on that style of BCDD the vacuum line comes from a valve that tells the BCDD to open and close. Maybe it's not working correctly?

 

 

 

Anyway. For the idle to be high more than just extra air is needed. It also must have fuel. So a gasket leak won't speed up the idle by itself.

 

Definitely check the throttle plates are closed.

[IsaacHeink]

I checked the throttle both throttle plates on Friday and they were both closed. 

 

Last week it ran better - shorter surges and idling around 1500 rpm. I didn't check the BCDD because I went out of town and didn't have time. I got back into town last night and when I went to start it this morning it wouldn't start. It sounds good when I crank it, but it just won't turn over.

I am going to try to start it when I get home and if it starts I'll try plugging the BCDD. If it doesn't start, I suppose I'm just SOL.