Got a 307 here that will not idle. So far I have replaced the fuel pump, cap and rotor, and rebuilt the carb. As long as I keep my foot on the gas it runs fine but let off of it and it dies. I'm thinking maybe water in the gas but I'm not sure. Tomorrow I will be running it off a gas can with known good gas. Any thing else it could be?
Vacuum leak is first on the list. That engine is new enough to have an EGR valve, and if it does, it could be faulty.
Sounds to me like a va***e leak. Is it the stock carb? does it have a adapter? Rare but it could be the intake manifold gasket. EDIT: Elpolacko beat me to it
My first thought was a vacuum leak also. Did you have this problem prior to doing all of the work on it? Jay
Yeah, it was running and driving fine a couple of weeks ago, felt a surge and started losing power for a few seconds. Did the work. Wouldn't idle then or now.
It could be one of the three things mentioned above ,I never even thought of a Egr stuck open .To me it could be a carb problem .First thing I would do is a complete tune up wires and plugs ,I doubt now its your egr and distributor .Read your plugs for color and get back to us .
How much throttle does it need to keep running? Take and slowly close the choke with one hand while keeping it running with the other, and see if it will idle when the choke is partially closed. If so, how far closed is it? This would indicate a vacuum leak someplace or a fuel supply/flow issue in the carb. If it dies as the choke goes closed...even with the slightest closure of the choke, this would indicate a rich condition. Pull off the PCV or whatever vacuum line you have that is the biggest...does it idle, or at least run without holding the throttle open? If so, you have a rich condition? Does this do this when cold or does it only do it when it is warmed up? What carb does it have? What ignition system does it have?
As the choke closes, it dies out. Fuel supply is good always getting fuel where it needs to be. Will not idle with PCV off. Both warm and cold, Quadrajet, Stock ignition with MSD cap and rotor.
I just thought of another thing...you mentioned it surged and lost poewr...then would not idle. Check the timing. Just this past weekend my neighbors o/t chevy truck with a 4.3 v6 did the same thing. It stumbled as he called it, and then ran sluggish for a minute and then ran fine. He got home, went to leave the next morning and it would start, but die unless he feathered the gas to keep it running. He fiddled with it, replaced the in tank fuel pump, cap, rotor, wires, plugs and it still acted up. He called me up and I went to look at it. I noticed it seemed a little slow when he'd rev it up, checked the timing and I could not find the mark anywhere near the timing tab. Did some more checking, and the timing had jumped. The gear was worn and chain stretched enough that it jumped time by what appeared only 1 tooth. we put a new timing chain and gear set in it, runs like a top again. Not saying this it it, but worth looking into.
Sounds like you blew out the rear seal in the intake and it blowing oil. It wouldent make a va***e leak in itself but it could have been sealing a little corner of the intake or something. Cheak your plugs to see if it is running lean in any or all of the cylinders.
forgot to mention that both times the intake gasket blew it also started to smoke AFTER it warmed up.
You say it dies when you close the choke? One possibility is the piston for the primary rods is stuck. (It could happen). Does it run any different if you disconnect the vacuum advance and plug the line? What year 307 and Q-jet?
A lot of them had aluminum intake manifolds that, over the years, would either leak past the gaskets, or the EGR p***age would burn out and develop a hole.
Check timing, Olds are bad about skipping a tooth on the timing chain when they have around 80K miles because that is when the plastic coating on the cam gear starts getting hard and chipping. Not uncommon for it to only jump one tooth. The surge was probably when the chain jumped.
I had a similar dilema with a 307 Olds. The internal part of the Q-jet idle circuit was the culprit. The idle metering tubes are very small and a speck of "something" would plug it (only one of the two tubes) and cause it to idle on 4 cylinders only. Had the carb apart several times. Finally, aggravated enough by now, tore down the carb one more time, and with 120psi air pressure blew through both idle metering tubes for a solid minute each one. Must have dislodged the speck and sent it into space (or somewhere), ***embled the carb and never had the poor idle condition again.
My neighbor wasted several afternoons replacing gaskets, etc. on a pickup acting exactly the same way. Finally he replaced the carb and the problem magically disappeared. (And it was a $20 junkyard carb that he installed!)
Before you tear it too far apart check the timing and if it appears off advance it a bit and see if it will start to idle better. My first thought was like everyone else in that it had a vacuum leak but I'm another one who had timing chain issues with an Olds engine and the symptoms were similar but I had a 2bbl and point distributor in that one. I'd be looking at every vacuum line and connection too as you might have knocked one loose or broken a brittle one when you were moving things around doing the tune up.
It was the intake manifold gasket. The ***es that rebuilt it didn't install it right. The manifold bolts could be taken off by finger and the rubber end pieces were not there. They had used a tube of Half *** Gasket (tm) and it had blown out. Redid it the right way and it fired right up and idles like a champ. When I drive it though it surges along but doesn't want to stall, so thats good. THIS IS A PUBLIC SERVICE ANNOUNCMENT: NEVER USE UNITED ENGINE SPE******TS IN WICHITA!!!!
Glad to hear you go *** figured out. A lot of professional mechanics (including myself) don't often use the included intake manifold end seals for use in V-type engine configurations. I was taught by someone I respect a great deal and found to be incredibly knowledgeable that in his experience the best way to handle the ends of the intake was to use a small punch and 'dogtrack' or dimple the intake where the seal would go. Then lay a bead of RTV along it prior to installation. His theory was that the 'dog-tracking' gave the RTV something to bite into. I've done it dozens of times without ill consequences. Jay
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