Rattle/ popping sound in exhaust plus idling rough

[danieldialtone]

I have an 85 tercel 4wd 5 speed wagon and it starts up and runs great and after driving it for a half hour or so it starts idling real rough and it almost dies unless i hit the gas real quick right before it feels like it is going to die and while its doing that it makes this popping sound in the exhaust. Also when it makes that popping sound is when i am not giving it any gas at all going down a hill or coasting under 30 MPH with the engine in gear or going up a hill or having the pedal down far trying to pass someone (under 35 MPH). It mostly does this when the engine is running pretty warm but if i drive like grandma on sunday and keep it smooth and slow it does not make that noise. One of my friends thinks it might be the catalytic converter. Another friend thinks there is raw gas getting in to the exhaust system causing the popping. It also has not been getting the best gas mileage and i just gave it a tune up not even 400 miles ago. Any ideas?

[dlb]

sounds like the ignition timing is incorrect. disconnect and plug the vacuum hoses that attach to the distributor and then use a timing light to check the timing. stock is 5* before top dead center, 10* BTDC is better. remember to reconnect the vacuum hoses after you're done. did you do the tune up or did someone else do it for you? if the timing was adjusted then, the bolt that keeps the distributor in place may not have been tightened enough and allowed the dizzy to turn, in effect adjusting the timing.

while you're at it, check to make sure all vacuum hoses are correctly hooked up cracked and broken. use the vacuum diagram on the underside of the hood to figure out what is supposed to go where. i think those are the best places to start.

[tercel4wdrules]

When checking the timing, if you have difficulties getting it timed correctly, I would check to make sure the distributor was installed and operating correctly. It's possible to install a tooth off and have issues like what you're describing. The backfire in the exhaust on deceleration could also be caused by a vacuum leak. Besides checking all of the vac hoses, the intake and exhaust manifold bolts tend to work themselves loose and cause massive vacuum leaks. There's one of those bolts you can't get to (one in the middle that's hidden under the carb heat shield) without either bending the shield or removing the carb. I've even had cars that were missing those bolts!

[Petros]

welcome to the list!

all above suggestions are good, I would also make sure the idle speed is set properly and the device opposite the throttle cable on the throttle shaft is set correctly. it is a vac operated diaphragm that prevents the throttle from closing too fast (lowers emissions), it is a simple adjustment.

Also, right next to this device is the AAP diaphragm (auxiliary acceleration pump) that runs a vac line to the bottom of the vacuum thermal switch on the water outlet on the head. These can leak fuel into the intake manifold and cause poor economy and run too rich at low speed. pull the vac line, if it is full of fuel it needs to be replaced, temp fix is to cap both ends. See the FSM on instructions how to find and test it. fairly easy fix if you have a replacement diaphragm.

good luck.

[danieldialtone]

thanks for the suggestions. Also in regards to what tercel4wdrules said, my manifold bolts were loose. also, I found a vacuum line that was completely disconnected that went from the bottom of the distributer to somewhere else. i put it back on and added some oil and now it has a very small occasional miss.
thats it. so i will see how it goes. thanks