Hello everyone, my '87 305 carbed will not idle. I thought it was the ignition module and replaced that but no luck. Everything else in the ignition system is new.

Is my problem most likely a plugged jet in the carb? That's what it sounds like but I wanted to hear some opinions before I tear apart the carb.

Thanks for any input.

 

Welcome Aboard!

Is the choke operating?

Is the mixture control solenoid active? You should hear a clicking when the ignition is turned on.

Is there fuel in the bowl? You can check by operating the throttle and observing the accelerator pump jets through the top of the air horn.

Have you tried increasing the idle via the stop screw?

 

Well I'm not sure if the choke is operating (the choke light doesn't come on). But when the car use to drive fine, the choke light would sometimes come on intermintently while idling, but the driveabilty did not change. I will check the fuel bowl to see if the bowl is stuck or something rather.Thanks for the help!!!

 

Ok, I looked at it more in detail this time. The engine will idle while cold (choke operating and hovering around 1500 rpm), but as soon as it gets warm, and I give it a little throttle the motor acts like it wants to idle at around 900 rpm, but ends up dying. It kinda acts like un-metered air is getting through the intake. I checked everywhere for a vacuum leak and no dice.

If I hold the pedal at ~ 1500 rpm it runs fine, let go, it dies.

Any ideas?

 

You might also have an EGR valve sticking open, leaking power brake booster, leaking PCV hose, or leak at the carb/intake flange. If there are no vacuum leaks there, start looking into fuel delivery.

If this is a stock carburetor, check the idle air bleed adjustment, M/C solenoid operation, and float level.

 

Yeah I found a bad vacuum hose on the EGR and replaced that but no luck, same outcome.

Where is the idle air bleed adjustment? Does M/C stand for manual choke?

All of this happened when I avoided a car accident and I lost control of the car and suddenly regained control. Right after that is when the car died and does not want to idle. It fires right up, but no idle.

Thanks again for all of your help.

 

M/C = Mixture Control Solenoid

The idle air bleed is on the top of the air horn (Item 12):



You might still want to verify the EGR is sealing internally, and not stuck partially open. Temporarily pinch or plug the brake booster hose to see if that has a vacuum leak.

 

Well yesterday I got it to idle (750 rpm) but it was pretty rough. Then all of a sudden w/o my foot on the gas, the rpms climbed to ~ 1200 rpm, smooth too, and it stayed there for a couple seconds, then went back down to 750 rpm. Did this back and forth for about 5 min until it just died.

I will try the egr and the hose for the brake booster.

So how do I check the M/C? And how do I check the idle air bleed? Just turn it and see if that helps?

 

Bump

I narrowed it down to the egr. If I clamp the vacuum hose coming off of the egr diaphragm, the car runs just like it came off the show room floor. No sputtering, no stalling, perfect. I take the vise grips off and it runs like ish. I thought I was getting a vacuum leak at the egr so i replaced it. No difference what so ever.

Could my problem be the solenoid??

Thanks.

 

Yes, the EGR solenoid may be leaking vacuum, OR the vacuum supply to the EGR solenoid is connected to the wrong vacuum port on the carburetor. The EGR solenoid should be connected to a timed vacuum port. There should be no vacuum at idle, and vacuum should start once the throttle is partially opened.

 

My vacuum source to the egr sol is in the front of the carb, just below where the vacuum line that comes out from the air cleaner housing.

I just got done installing the new sol and it does the same thing. I pinch the same line as before (vacuum line from egr to sol) and it works fine.

The idling is no longer the issue, it does that fine. Now it bogs SUPER bad when I roll onto the throttle from a start, or when I am cruising and try to pass someone. What the heck is the problem here?? It is driving me nuts! Any thoughts?

Thanks.

 

Well...I think it's the EGR system. Check the voltage on the Vac Sensor/Solinoid...it could be a bad wire. There should be 5v between the black and grey {I think}...and the third wire, is an output wire to the ECM that tells the computer how much vacuum there is by voltage feed back...just look it up in the manual or internet.
ALSO....Check the EGR for carbon build up and the type of EGR...Some are run by exhaust back pressure and cause idle problems,..which means taking a look at the cat for damage or plugged.
....Take a squirt bottle of water, set it to SPRAY or MIST. Rev the engine to 2500 or 3000rpm. squirt the whole bottle{or two) into the intake while holding the rpm's. Take the EGR off, it should be full of carbon now....clean it and reinstall it. Do it over. The hydrogen in the water chemically reacts with the carbon splitting it apart and blowing it out the exhaust and some ends up in the EGR. I've been doing this on all my engines over the years....it keeps them clean.

 

Sounds like some good advice. Thank you. But I only have 2 wires total that go to the egr sol. No matter what rpm I'm at it stays at ~14V. A couple of days ago I plugged the same vac line as before and it did not make it run any better. Oh and I have a brand new egr and sol now....

I can kind of improve the problem by messing with the idle air screw but it still does not solve the problem. No CEL either.

I do not know if this problem is related, but the tranny does not like to shift unless I let off the gas for a brief moment, then it shifts. It does this really bad in the 3-4 shift. And when it does this it shifts like it has a shift kit (car is stock), extremely firm.

So I'm pretty sure something is wrong with the carb...no? But I am about ready to drive this thing off of a cliff. Thank god this isn't my dd anymore.

 

Sorry...your right...the solinoid has 2 wires and the Vac sensor has 3. I think the computer reads the vac voltage and tells the EGR solinoid what to do. It should pulse quickly to regulate the vacuum being bled off the EGR. I'm not sure , but it could be PWM {Pulse Width Modulated}.
Check the exhaust system...a new EGR will behave the same way if there is a problem in the exhaust! Ant idea what type it is? My Monte SS has an 'N' stamped on the top for 'Non-Back Pressure'
Also.... I had a bad TPS do wierd things to the idle and tranny....so check that too!
Anyway...keep plugging away...don't give up yet

 

Ok I just got done changing out my carb with an OEM remaned one from Holley that I got from Summit. Car runs excellent. I'm glad that was my problem, and now I can get the car back on the road again.

Thanks again to everyone for your help. It is much appreciated!