Rough/low rpm idle, bogs and dies around 400 rpm

[fffutr]

My '87 started just running rough on low rpm's and it wants to bog and die at stoplights. I took the air filter cover off and I immediately heard a sucking sound. Figure it must be a vacuum issue, and read that I might have to cap off the AAP. Thing is, it gets really cold up here in Iceland, and I thought I might need it. Someone mentioned turning up the idle, but I can't find an adjuster screw, can someone please post a photo of it?

Also read that a carb rebuild might cause more problems than it solves, would you guys recommend finding a used one or even buying a new one for like $120 instead of the $50 rebuild?

I hope someone has time to point me in the right direction tonight, we have a hurricane force storm coming in tomorrow afternoon and I would love to not be stuck =)

[Mark]

Sounds like a vacuum leak to me. I'd look carefully around the carb and see if there are any hoses that are disconnected. Some of them come off pretty easily. There is one that is connected to the bottom of the air cleaner. That one usually pops off on mine when I remove the air cleaner. Even if none of the hoses are leaking, a diaphragm component could be leaking internally (like the AAP). You could disconnect the vacuum hoses to each of these one at a time and plug the end of the hose with your finger. If the idle smooths out, you've found the component with the vacuum leak.
By the way, the AAP only works when the engine is cold. If that is the leaking component, you could disconnect/cap it and plug the hose and just let the car idle for awhile before driving to warm it up. That way the AAP doesn't even need to be used.
It would be a shame to go to the trouble of rebuilding the carb, when the problem might just a vacuum leak.

[fffutr]

Sounds like a vacuum leak to me. I'd look carefully around the carb and see if there are any hoses that are disconnected. Some of them come off pretty easily. There is one that is connected to the bottom of the air cleaner. That one usually pops off on mine when I remove the air cleaner. Even if none of the hoses are leaking, a diaphragm component could be leaking internally (like the AAP). You could disconnect the vacuum hoses to each of these one at a time and plug the end of the hose with your finger. If the idle smooths out, you've found the component with the vacuum leak.
By the way, the AAP only works when the engine is cold. If that is the leaking component, you could disconnect/cap it and plug the hose and just let the car idle for awhile before driving to warm it up. That way the AAP doesn't even need to be used.
It would be a shame to go to the trouble of rebuilding the carb, when the problem might just a vacuum leak.

Thank you so much for your guidance, Mark. I feel way less worried now =)

[xirdneh]

when you hear the sucking noise it most likely is the hose that attaches under air filter housing (comes out of carb base on driverside and attaches under housing)

[fffutr]

when you hear the sucking noise it most likely is the hose that attaches under air filter housing (comes out of carb base on driverside and attaches under housing)

Thanks for the heads up, I'll look for that. Also, you're right about that road noise! Really want to see about putting down some polyurethane under the carpet up front

[irowiki]

When you say "low RPM's" what RPM is it exactly?

[dlb]

Also read that a carb rebuild might cause more problems than it solves, would you guys recommend finding a used one or even buying a new one for like $120 instead of the $50 rebuild?

when you buy a used carb, there is no guarantee it doesn't have more problems than your old one -- why pay money for another set of problems?

i believe all the 'new' carbs are actually remanufactured, and people on the forum that have bought them have noted leaks from the throttle shaft (just like all the 'old' carbs), which happens with age. so i don't know that it's worth the extra money.

rebuilding the carb shouldn't cause any more problems, as long as you are thorough and follow the instructions.

all this being said, i agree with the others that it is most likely a vacuum leak. make sure all the hoses are connected and properly routed.

[irowiki]

Does it only do this when cold, or when warmed up too?

[Petros]

it is normal to hear a sucking sound with the air clean assembly off. the carb works by sucking air down the barrels, and it is normal to hear a "hiss" with the air clean assembly off the carb.

With the air filter assembly on it, verify all of the vac lines are connected and routed properly based on the vacuum line routing diagram for your car. follow each one from start to finish to verify it is working okay, no cracks or leaks, and goes tot he correct location

You can also check for vac leaks using some carb spray, with the engine running spray it around the vac lines, base of the carb all gasket lines, and vac operated components. the vac leak will suck in the spray and change the speed of the engine (some brands will increase the idle speed, some will slow it down, depending if it is flammable or not).

the idle speed adjustment is on the crank where the throttle cable attaches to the carb, next to the body of the carb. There is both a cold idle speed adjustment, and a normal warm idle speed adjustment, which is the larger of the two screws. This is presuming you have a similar carb where you live as the one on the North American cars.

Good luck.

[fffutr]

When you say "low RPM's" what RPM is it exactly?

Struggles to maintain 500 rpm's, dies at 400.

[fffutr]

it is normal to hear a sucking sound with the air clean assembly off. the carb works by sucking air down the barrels, and it is normal to hear a "hiss" with the air clean assembly off the carb.

You can also check for vac leaks using some carb spray, with the engine running spray it around the vac lines, base of the carb all gasket lines, and vac operated components. the vac leak will suck in the spray and change the speed of the engine (some brands will increase the idle speed, some will slow it down, depending if it is flammable or not).

Good luck.

Reseated all the vac-hoses, and now it ticks at 800 rpm's after 20 secs of warmup. Thanks everyone for helpful advice.

[irowiki]

Turn your idle up just a tad too.