the Mistery deepens, expert needed

[86sebring]

I need help with my carburated 302. This is starting to drive me nuts. It started when out of the blue it would not idle anymore, just shut off. It would either idle at 2000RPM or not at all. I checked the timing which was good at 10° at 1000RPM and about 38° at 3000. So I rebuilt the edelbrock carb, checked everything and put it back together, but the condition was still the same, no idle and very good top end power. I installed a holley carb-- same situation.
I played with the vacuum advance in the distributor and suddenly it idled fine, I thought it was fixed, but after driving for a while the condition returned, no idle, slight stuttering in low RPM's, but good top end power.
Last night I switched to a Mallory electronic distributor. It idled fine right off the bat, but after driving for a while when it got warm, the condition returned.
So it is not the carb, it is not the distributor, I checked for leaks around the intake and carb, the timing is set correctly, what gives??? What other components influence the idle
I don't know what else to check

 

[69Rcode_Mach1]

HAHAHAHA this sounds like the same **** that I am going through. I am eager to hear the answer. Hey atleast you can get your timing straight I can't even get that. First time engine builders woes.

 

[2nd Mustang]

Do you know how much vacuum you were pulling at idle when it was running well? How about fuel filter? Believe it or not, but a poster had a similar problem a long while ago, it turned out to be his clogged air filter.

 

[bnickel]

sounds like you have a vacuum leak. try spraying carb cleaner all around the carb and intake to see if it changes the idle at all. could also be a bad timing chain but you would normally see that with the timing light since the the timing would be jumping around all over the place. i'd bet good money on a vacuum leak

 

[rbohm]

a few other possibilities;

1: a dying fuel pump

2: a clogged fuel line(it has happened to me)

3: vapor lock

 

[2nd Mustang]

Did you check for vacuum leaks around the area where the intake manifold connects to the heads? This sometimes is overlooked as a lot of people assume it's tight. I know I did that.

 

[Hissing Cobra]

sounds like you have a vacuum leak. try spraying carb cleaner all around the carb and intake to see if it changes the idle at all. could also be a bad timing chain but you would normally see that with the timing light since the the timing would be jumping around all over the place. i'd bet good money on a vacuum leak

This is very good to do. I had a vacuum leak on my '93 Ford Escort that I had to find myself. First I took it to the Ford dealer and they tried to tell me that the catalytic converter was clogged $300.00+ to replace it.) Then when I took it there for them to fix it, they called me back and said that it was fine and that the MAP sensor was bad ($100.00+ to fix it.) Fortunately for me, they didn't have one in stock so I went and picked up the car (paying them $20.00 for "diagnosing" my problem.)

Well, the bastards lied! When I went home, I popped the hood and could hear a "hissing" sound. With my wife pressing on the gas and me spraying carb cleaner, I found out my intake gasket was gone. Everytime I sprayed around the intake, the idle would smooth out. Five dollars later (new gasket) and an hour's worth of my time, and I was back on the road without a problem. Because of this, I will never go back to that Ford dealer again.

I also recommend looking for vacuum leaks. Good luck!

 

[66_stang]

same exact thing happened to me, turned out the gasket on the carb had come loose. There was a huge loud hissing noise though in my engine bay, not sure if u have that or not. Im willing to bet its a vacuum issue,.

 

[86sebring]

I got it, finally thanks for all the help
I replaced both vaccumhoses and the PCV valve, and "voila" idles like a champ
Hopefully this info will help somone else with the same problem.
It has been a very frustrating time, I was ready to lock the garage and loose the key, but now that this thing runs, I will again enjoy it
thanks again

 

[chrua]

I had the same problem. Cleaned out the fuel line and had gottennew intake manifold a few months earlier and had not plugged up a hole in the back of it.

 

[hungrymonkey]

I had the clogged air filter about 4 years ago.

It would idle fine, but would die with any amount of throttle.

Then I would pull the air cleaner and try to figure out what was going on, then it would run fine.

It took about an hour to realize that it was the air filter killing the truck, and not from me sitting behind the steering wheel.