I'm worried....my 1st gen has been good to me. I have noticed this problem happening and I need some feedback from you guys to help me decide what to do. This is something that has been going on for a week or two. I've had the car for about two years.

It happens when I'm driving in the city. Minor stop and go. When I approach a light and sit at a dead stop with the clutch in, at idle- the needle bobs up and down as the speed of the engine irratically idles. A light touch of the gas pedal is required to keep it from stalling as I'm sitting there. I've been witness to the RPM's going as low as 500 or so and then I have to apply the gas to keep it going. At that point it still runs irratically and goes back to being smooth once I drive off. This doesn't happen all of the time, but more frequently than I would like. It sounds like this......blub blub blub blub blub blub blub blub blub then when I drive off- bruuuuuuuuuummmmmmmmmmmmmmmmmmmmmmmm. You know

My first thought was that it was the carbuerator that needed some attention. I purchased carb cleaner. Took the filter housing off and cleaned the exterior of the carb which had minimal dirt. Gave it a few shots inside the carb and blew out some carbon. Thought I fixed it at that point, but was driving around today and noticed it doing it again.

My thoughts, correct me if I'm wrong- possible fuel issue (clogging, dirty fuel filter etc) or attention to the carb is required. How will I know if it is something major where say the engine needs to be replaced? The engine is in great shape. All the seals are good, no oil leaks and very clean. Well maintained original engine with approximatly 90k miles on it. I drive it nicely.

What should I do?

Thanks in advance.

Mark in San Diego/CA

 

Sounds like inconsistent fuel delivery.. Pop a new filter in first.. If that doesn't solve it.. Maybe a new fuel pump is in order..

 

I just read this on Atkins Rotary. Would this be the best option to address?
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After my car has warmed up the RPMs keep bouncing up and down, what is wrong?
You probably need a new BAC valve which is located on the upper dynamic chamber on you're intake manifold. You might also need a new Throttle Position Sensor.


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I would have trouble believing it is fuel related because it doesn't irratically idle all the time. There are plenty of lights I hit where it doesn't act that way. The fuel filter was replaced not too long ago.

 

I have a similar issue that I've been working through on my '81 12A.

My idle started to "hunt" (brrr...brrr...brrr...), so I rebuilt my carb. It hadn't been rebuilt in years. The rebuild didn't fix the problem.

I started tuning the Air/Fuel ration screw and idle adjustment screw as it is idling was high at 1,200 RPMs. I am convinced it is a vacuum leak or timing-setting that I can't nail down, as I've done the following:
1. New plugs
2. New fuel filter
3. Carb rebuild
4. New Nology plug wires
5. New leading ignition coil
6. replaced the obviously brittle vacuum hoses.

(I still have the full-emissions junk; except the air pump blows to nothing as I have a Racing Beat header and long primary exhaust system w/ presilencers. This never caused a problem in all the years I've had this setup.)

One thing that made a noticable difference:
I tweaked the distributor clockwise and it almost fixed the "hunting" idle; however, it is still surging at a slightly noticable rate. I'll post more as I can get time to play with it. I also lined up my pulley's timing mark to the second notch, and put my rotor cap to point at the rear before I tweaked the distributor assembly with the car running.

 

this is for a GSL-SE fuel injected 13b engine...from your profile you have a GSL...which doesn't have what is described above

 

Thank you BIZZARO. That sounded pretty intense. I just dont want to replace anything that doesn't need to be replaced. You know. Maybe a local shop could diagnois it?

 

Anyone in San Diego wanna make some extra bucks using their knowledge of putting on a Racing Beat engine torque brace??

 

i'm assuming you are still learning about your car...i suggest you use the forum for the most information you can get out of it before paying someone to do the work for you...sounds like your problem is simple...you just have to find it...keep searching, fix it yourself and you'll appreciate your car alot more when you do good luck

 

I would hope that you can install a torque brace without having to pay someone. I mean as long as you have at least one good hand, you should be able to tackle that mod.

and if you've got two good hands, then it'll take half as long and you can clap when you're done.

 

Thoroughly check for any vacuum leaks before you do anything else. This will cost you nothing and should be done anyway if it hasn't already. You can take a lenght of hose and hold one end to your ear, use the other end to listen around the vacuum lines and you should hear any leaks very clearly (works like a stethoscope).

I don't think its a filter or pump issue, otherwise you would see it at times of high demand, not idling. Could possibly be something with your idle circuit, but save that for later.

If you can't find a vacuum leak, then I would start with all the usual tune up type stuff. Get that out of the way and see if you still have a problem. Keep us posted.

 

That's what I'm talkin about. Thanks Kentetsu. Now I will just have to figure out exactly how to do what you're talking about and where those vacuum lines are to test. I know it's not the most difficult car to work on, but a lot of the hoses and lines and wires I have no idea what they do or how to determine if one or any need attention. Can you give me a general area to locating these hoses for vacuum leaks- where they are and what they're connected to to check for leakage? The stethoscope procedure makes perfect sense to me, but where to plug the end that isn't up to my ear to hear for leaks is what I might have trouble figuring out. Basically where these vacuum lines are. I had a hard time believing it was a fuel delivery problem myself, but you know- since I've cleaned the carb (exterior and interior) with carb spray, the problem seems to be almost non-existent. I have noticed it less. The irratic idling doesn't occur at every light I sit at like it used to. Must have done something. I have almost used a full tank of fuel with carb cleaner additive which might also have contributed in part to fixing the problem. Like you say though- checking for leaks won't cost anything. It hasn't been done, and I would like to do it anyway just to make sure. Explaination of where these lines are would be helpful.

Many thanks

 

Oh, also- your car looks great! Got any full size pictures to send me?? I would like to see a larger picture to see what wheels you've got.

 

The end of the hose that is not up to your ear is the end that you move around. Just move the end along the lenght of any vacuum hose and if there is a leak you should be able to hear it. For fun, place the end right on the engine block and you can hear all of the bearings and everything.

As far as which vacuum line to check.....all of them.

My avitar is just the standard one, not custom. My car looks just like that one, except for the wheels so no idea what they are. Sorry.....

Good luck with your issue, hopefully it won't return...

 

My dad taught me a little trick to check for vacuum leaks.

Take some pliers, pinch each vacuum hose so that it seals itself, and if the idle changes at all (I think if it goes up, then that's the leak. I guess if it goes down or dies, then it must be a fuel line :P), then you've found your problem. To me, that's alot easier than spraying stuff and then having to worry about electrical components and what not. [Especially since the alternator sits right on top.]

I haven't really had much success with the 'stethoscope' method. Of course, then again, I haven't had much success with anything.

P.S. I also remember hearing that if you try to turn the idle mixture or idle speed screw down to adjust the idle some, if it doesn't go below 1k RPM, then it's a vacuum leak. Of course, I have no experience with that, since I don't think I have a vacuum leak, so don't take my word for it.

 

Vacuum leak.

Once found and resolved, double check idle mix and idle speed, adjust as needed.

 

check the west forum. look for chris @ SPDracing.com
Or drive up to LA and I will install it for ya.