Bad idle/stall when in drive

The last month or two I have noticed my idle getting a little rough when I am in drive. When I idle in park it is pretty smooth and consistent. If I am sitting in drive in my driveway with foot on the brake, the idle gets a tad rough at times but not bad enough so I would think that the car is going to stall. When I am driving and I coast to a stop and then sit there in drive (like at a stoplight) the car tries to stall out from time to time. Then when I accelerate from the stop the car hesitates at first and then takes off. I started looking for vacuum leaks, checked the PCV valve checked fuel filters/lines. I am going to check the vacuum line to the modulator on the trans tomorrow. The carb floats are working fine and the level is perfect. Anybody have any ideas what could cause this kind of rough idle that only happens when the car is being driven? This problem is getting pretty especially when there is traffic.

Thanks

Scott

Vacuum leak, when was the last time the fuel filter was changed?

I was thinking vacuum leak too. I didn't notice any leak when I was spraying the ether around. I am going to check again. I just changed the fuel filter tonight.

Scott

Check your timing as well. If your like most of us and have found the need to merge rather quickly, your timing may have moved.

I am going to throw the timing light on it again. I checked it about a week ago and it was where it was supposed to be. I wasn't thinking in that direction... good idea.

scott

Hi Scott,

If you've got points and condenser, then check those aswell.

DJ

I like the feedback, my car is having similar problems so I'm learning some stuff as well! I'm thinking mine has a vacuum leak.

I am having a similar problem, going to look at changing my fuel filter. How would I go about testing for a vacuum leak on my 73?

Incorrect idle mixture setting

Heat soak/vapor lock

I have a pertronix flamethrower 3 and ignitor 3 coil on the mustang. I installed these parts last weekend but the trouble started well before I did that.

Scott

As for the vacuum leak you can spot shoot some starting fluid around the vacuum lines and intake gaskets to see if the RPM's pick up. If they do, there's your leak

If there are no vacuum leaks and the timing is correct, it may be that go/varnish/dirt has gotten into the idle circuit and or the idle air bleeds. This would cause it to run rich at idle and "load up" (gas foul the plugs). Just a thought. Chuck

I had a similar problem and it was driving me nuts. Turns out the brake booster was the vacuum leak. I would disable your and see if the symptoms go away.

Guys, thanks for all of the input. I have checked the vacuum lines and booster. No leaks. I thought the booster might have been the culprit because I did replace that recently. That turned out to not be the problem. I checked the timing again and it is spot on. I replaced the fuel filters and checked the float level. Everything is good there. I recently installed an a pertronix flamethrower 3 and ignitor 3. I never did anything with the gap of the spark plugs. Could that be an issue? I am getting to the point where I will rebuild the carburetor again in the hopes that there is something in there. I am running out of simple little things to check. Worst case scenario is that I take the car over to a local garage here. The guy is an old school hot rodder and I have seen him do some really great things with cars that were acting up. I would rather figure it out myself and try to learn something but it looks like this is outside the realm of my knowledge.

Scott

if you have a holley richen up the idle air bleed screws turn both to 1.5 turns out as a start.

I am thinking that that is what is happening. I just pulled my spark plugs and 4 out of 8 are fouled. I just put them in 5 months ago. All 8 also have a pretty good amount of oil on the threads. I don't think I like where this is headed.

Scott

well if it was running well before the petronix III that is one thing.

oil on the threads, means valve stem seals need to be looked at. Big job as far as work involved. I did mine this summer took a full day and i did not enjoy it even with help from the engine builder. that is if the plugs are fowled with oil

if the plugs are fouled with fuel, that means weak spark or incorrect timing.

I do not know exactly what you are running on your engine but i will give you this direction to look into.

If you changed to the petronix III and used the petronix Coil and changed the ignition wires. what ignition wires did you change to?

if you changed the ignition wires to the recommended petronix 8mm spiral core or what they claim are shielded wires, take them off the car and throw them out.

Get a regular Ford Carbon filament standard set of V8 ignition wires. start the car and let it run to burn off the plug fouling, then check the timing you will see it changed. reset the timing to what you want and go for a spin.

I went through this i had some 8 and 9mm MSD wires and the engine ran like pure garbage until i advanced the timing to the moon. miss on acceleration, ran rough,etc... changed out the aftermarket ignition wires for old school regular ignition wires. instantly the engine ran almost perfect.

before you start to freak out about the plugs being fowled which is more a symptom of a spark problem, look into the ignition wires themselves then the carburetor.

I personally hate the petronix III. the I or II work better with our cars if you have the stock tachometer.

i hate high powered coils also they cause all kinds of radio interference issues.

before you go nuts, first see what ignition wires you have. anything other then stock, throw them out, and grab a set of regular ignition wires no frills no special insulation, no special silicon wrappers. just good old carbon filaments, install them and see what happens i'm sure there will be tuning required but you want to see the effect on your car.

If you have an air compressor, changing the valve seals is not that difficult. It's just time consuming. Go to your local auto store and get the seals, air adapter that screws in where your plugs are(I use 80 lbs.) to hold the valves up, and a spring compression wrench (K-D 912)

OK, thanks for the tips. I have basic stock autolite ignition wires in the car now. Had some of the aftermarket ones. Put the new plugs in today as well as the new stock wires. Started the car up and let it idle for a while. It is raining out now so I didn't take the car out anywhere. It looks like there is still that idling problem from what I could see in the garage but I will know more when I can get it out on the road for a while. I am also going to throw the timing light back on it tomorrow and see what it is looking like.

No AC in my car so at least that is one less thing to go wrong. I was sticking to the seats in the car all summer long though....

Scott