Car I am driving daily has this problem that comes and goes and I cant figure out what it is.

First off Dist was replaced last year after ignition module went out. carb was rebuilt twice about 3 and 4 years ago.

The problem is this, every now and then and right now is when it is happening again the engine wants to lope at idle in gear like it has a cam you hit the throttle and it wants to run horrible with hesitation and the engine just shakes like crazy running rough. You put the AC on it wont even idle with the step up solenoid active.

When I did some diagnostic couple weeks ago when this came up I found out engine vacuum is low and if you put the AC on and put it in gear when it barely runs engine vacuum is bouncing around at 0 - 5 inches of vacuum. With the engine running in neutral with AC off vacuum was at 16 inches with the ac on with step up solenoid bringing RPM back up to where it was without the AC on engine vacuum is down to about 11-12 inches of vacuum.

Ive already played with timing and played with adjusting the carb but this comes and goes which has me confused to the point that I think its just time to pull the old 2V carb off and put a new one on.

I want to ask has anyone here ever heard of a screwed up carburetor acting like this where when it barely runs it wants to have no vacuum when under load like putting the AC on?

I hate to fork over nearly $400 for a reman carb and find out this isn't it. I just don't believe it could be anything with the engine itself because it wouldn't come and go as a failure mechanically is the end of the line. I don't know if there is something in the carb that is causing this or if its the vacuum leak that it has around the throttle shaft due to worn throttle shaft bushings or if its just compounded by a lot of things.

All I know is I want to fix it but I have never seen anything like this. THe way it acts, it acts like its a lack of fuel to me but I am unsure as I have never seen engine vacuum act like this before.

 

What engine is this? Does it have the ignition module bolted to the base of the distributor? If so, it could have failed again. The Ford TFI module in this configuration is notorious for overheating. This causes poor running as you described. In this state, the engine will likely not generate much vacuum, so you can't really trust that reading.

I relocated my TFI module to the inner fender on my Mustang:

https://photos.google.com/share/AF1Q...F5VW82R0FnSGF3

I never had any problems, but this is cheap insurance to prevent it from happening.

 

Not exactly a ford engine. I didn't want to go into too much detail on the specifics but this is a old carbed 3.3L V6 with one of those dualjet 2V carbs.

When the ignition module went out last time it did have random bouts before it finally failed and wouldn't run anymore. But it was dropping dead it wasn't running rough and doing what it is doing now.

 

I did some checking cause now its here to stay and hasn't gone. engine runs fine at rpm but is sluggish and wont idle for ****. I checked the EGR valve to see if it was maybe hung open but nope its closed. I manually opened the EGR valve by hand and it ran even worse.

I don't think its spark related because when I power break it and put my foot to the floor the rpm wont go much over 1,200 rpm indicating a lack of fuel/air. I also checked the tail pipe today at idle the exhaust coming out is scolding hot telling me that the thing is either running rich as hell and making the converter work over time or its running lean as hell.

I have a ignition module coming in a Delphi unit from rock auto but I am going to order a reman dualjet carb today from summit as its cheaper than else where with the core and going to swap it in.

 

Low vacuum at idle, might be a stuck EGR valve. Vacuum at idle should be high. You've got a vacuum leak somewhere

 

I noticed you said the throttle bushings are worn. STart thr engine and then spray starting fluid around the throttle shaft bushings and listen for a change. Also, you may have a pin hole leak in your EGR valve. Does it only happen when the engine is warm?

 

The low vacuum comes in when I put the engine under a load. With no load and at idle the vacuum is over 15". But when the engine barely runs in gear from being put under a load the vacuum goes to crap. I thought it might be a stuck EGR valve but I pulled the EGR valve and poured water in it to see and it didn't leak any water. I also manually opened it as I can push on the diaphragm itself and when I opened the EGR slightly there was a quick change in the engine running worse. Right now the engine is steadily runny horrible its not longer coming and going from time to time. The exhaust coming out of the tail pipe is scalding hot which tells me the engine is either running lean or rich. If I didn't have a converter then I would say running lean but with a converter a rich condition would make the converter work over time. Another thing I noticed is where my engine should be running 180 - 190 degrees in this 80 - 90 degree weather the engine is actually running 160 - 170 degrees. I know a lean condition results in higher cylinder temp and a rich condition a lower cylinder temp. It would explain why under no load closing the choke smooths the engine out but while under load it stalls out. Most likely whats happening from what I am seeing is one circuit is running way too rich for idle but off idle its fine.

But the thing that is confusing me is normally a flooding condition when you power brake it the engine will stumble then as it clears out it will want to race up. This engine foot on the floor while power braking wont go over 1200 rpm. But going down the road you floor it, there is a pop back through the carb which I have always been under the impression is a lean condition the engine slowly builds rpm but after 1200 - 1500 rpm the engine takes off accelerating normally up to 4500 rpm before shifting. Which is not a symptom of lack of fuel as if that was the case the engine wouldn't want to do anything but idle.

As far as vacuum leaks, I already checked there is none and there is no point in wasting time as a vacuum leak doesn't come and go. If it only did it when hot or cold then sure but this is all the time now and it doesn't matter how cold or how hot the engine is. I even checked the vacuum modulator to make sure the hose wasn't broke and just sucking air since the transmission shifts hard. But now with the engine running like it is now like pure crap the transmission shifts smooth now go figure.

I have a brand new Delphi ignition module just incase if there is something going on there that might be causing that but I keep coming back to this old carb that's been rebuilt atleast 2 to 3 times already and has wear that a rebuild kit wont correct. If there is trash in the carb that some how got past the filter its also possible that's why it came and gone twice but now is sticking around, probably nothing more than a piece of trash in the system.

Yep they are worn, that's why I ordered a reman vs trying to rebuild this thing yet again. I can physically feel and see the shaft move side to side when I move the shaft forward and backwards to the front and back of the carb. When I initially was diagnosing this problem when it came up a couple weeks ago I thought vacuum leak as closing the choke manually caused the engine to speed up and smooth out the idle. Spraying carb cleaner on the throttle shafts resulted in the same increase in rpm and smoothing out. Spraying along base of carb, around EGR valve, around vacuum hoses, ect did not result in a change. I futhered my diagnostic by having the car held in gear with the AC on where it was barely idling even with the step up solenoid which I have preset to 1200 rpm in neutral to give me 700 rpm in gear. Closing the choke the same amount resulted in a instant stall. Which is why I think there is something going on with the carb itself which is causing my problem.

I already replaced the dist last year as the ignition module went out and being a 30+ year old unit it was cheaper to buy a whole distributor than just the module itself. The problem then was a random dropping dead for no reason that would come in randomly with no clear pattern to denote what it could be. That is till the module finally burned up and it stayed dead.

In this case it wasn't dropping dead randomly it just did this to me twice and cleared up. First time I left work it was doing it I nailed the throttle a couple times and by time I got home it cleared out and was running fine. A couple weeks after that it came up on a Saturday when I was adjusting the choke and choke pull off as the choke wasn't adjusted right and the pull off was too much so engine wouldn't go on a proper fast idle. This is when I diagnosed it as best as I could since it stayed this way. I couldn't figure it out nor make heads or tails of it outside of thinking it might be a carb problem. Needless to say I drove the car to work Monday nailed the throttle a couple times didn't clear out, on my way home at lunch time nailed the throttle a couple times and it cleared out again. Drove it another couple weeks or so and it happened again this time on a Friday leaving work nailed the throttle numerous times and it didn't clear up. As of now nearly a week later as its already Thursday the engine is still running the same way with no power, shaking on take off idling way lower than it was before and don't even think about turning the ac on as even with the step up solenoid which is set at 1200 rpm in neutral wont even keep the engine idling.

Right now the car idles in gear with the AC off like it has a cam in it. Reminds me of the old trick of closing the choke slightly making the engine run slightly rich to get a artificial lope to make it like you have a bigger cam than you do. This reminds me of that.

As far as when it happens, its not a hot/cold thing, it started doing it upon start up and didn't go away with heat. It only went away with nailing the throttle a couple times but now what ever is failing has gotten to the point that it wont clear out now and it just steadily runs like this cold or hot.

as far as EGR goes, Ive had an EGR stuck open before, while it is similar to how this is running I have never seen a EGR valve stuck on a carbed application and actually run on its own. Every one I have seen you had to toe and heel it to keep it running.

Now a pin hole I don't know I did pull the EGR off and poured water in it and nothing came out. A EGR valve isn't that expensive so that could be a next trick to try if the carb doesn't fix it. But even with a pin hole I don't see why it would clear up and work fine for weeks then come back and clear up again then come back and not clear up. A mechanical failure is one and done it either failed or it didn't. Ive seen electrical how ever come and go. Never really seen a carb do that but doesn't mean it couldn't happen. I know the engine builder I know I talked to about how hot the exhaust coming out of the tail pipe is he told me instantly engine is running lean as hell. I told him with my low engine temps that are lower than usual running rich seems to make more sense and the heat is coming from a overworking converter.

In any case the carb wasn't but $300 from summit reman, and this car had a lack of power for a while now so even if the reman carb doesn't fix this running problem if it just brings back the throttle response and performance of the engine I wont complain.

All I know is this is some weird **** that I am trying to figure out and this car nothing has ever been easy everything has been hard to diagnosis as nothing makes sense. Like the whole ignition module, ignition modules usually don't go faulty from time to time they either work or they don't.

 

Little update, I found the problem by luck. the HEI cap is burned through and through again. So I am doing a complete tune up along with replacing the ignition module and the coil. Only things that can burn the cap like this is a missing ground strap in the HEI cap which it isn't, or a high resistant coil/plug wires.

 

Engine runs better but same thing wont idle in gear. Close the choke to a 1/8" opening engine clears up and runs smooth with 20" of vacuum. Let the choke open up vacuum is around 13 to 14 inches and goes to 0 inches when placing in gear as engine stalls out.

I come back to running lean. the passenger side idle mixture screw can be fully seated on the dualjet carb and doesn't make a difference the driver side idle mixture screw gets in about 1" out before vacuum starts to drop and starts to stall out.

Ive used brake cleaner around all the vacuum hoses and no change. Even sprayed it around the intake manifold and still no change. Little in the throat of the carb engine speeds up instantly. So if there is a vacuum leak some where I cant find it. I even unplugged the vacuum modulator on the th250 transmission and the engine wont even run in neutral with it unplugged which tells me it cant be a leak at that hose.

So I am at a loss, I did replace the EGR valve today as I double checked it and brake clean was dribbling out of the egr valve. Only other thing I can think of is maybe the intake manifold has a vacuum leak at one of the intake manifold gasket ports and is leaking internally to the motor but I hate to tear the motor apart for that and find nothing.

 

What carb is on it ? Might try plugging both valve cover holes and see if the idle changes.

 

Its a dualjet, basically its a 2V version of the OE quadrajunk GM used.

Ive made some progress I found some problems and corrected them engine runs smoother at speed and everything but this not idling in gear is what I am still left with.

I pulled the pcv valve hose at the carb base off and plugged it with my finger and no change but that doesn't help if there is a vacuum leak on the inside of the engine.

To plug both valve covers I would have to take and pull the hose at the carb plug the carb, pull the hose at the PCV valve and plug the pcv valve then I can place my hand over the metal tube for the fresh air into the crank case.

 

Ok, I've never fooled with a 2 bbl Rochester, but they were pretty good reliable carbs in their day. The Q-jets were to, till they started having problems.

 

Found the problem. Reason why the engine wont idle is the passenger side idle circuit is blocked off. Summit gave me a bunch of bs about sending the carb back in but with a 8 to 10 business day time frame I cant be that long without a vehicle.

They are sending me another one though.

Carb cleaner through the straw into passnegerside barrel resulted in a increase in idle speed and smoothness. Spray in the riverside barrel there was no change.

Like to know how this so called wet flowtested reman carb got through QC with one idle circuit non functional.