bxd76

Hi all.

1978 Delta 88 with the Olds 350 in it.
110,000 miles.

Starts well. Accelerates well with 1/4 throttle or more.

But when I’m on the throttle lightly it surges.

Engine slightly loses power then surges back. Its not an extreme bucking but I can definitely feel it.

Things that have been taken care of lately:
Spark plugs
all vacuum hoses
tune up (timing. Mixture screws. Idle.)
air filter
Fuel pump

The only other symptom I’m having is after I start the car, it’s on fast idle like it should be when cold.
Doesn’t matter how long I wait, when I put it in gear the first time it wants to stall. If I shift real quick back to park, I can save it from stalling. Then I try to go back to drive and it will be OK.
If I don’t catch it and it does stall, I restart it and it goes into gear just fine. I mean it doesn’t stall. Not sure if this is related to surge or not.

Appreciate the feedback!!

Brian

gs72

Disconnect the egr valve vac line and plug it. Then drive it and see if the surge goes away.

Sugar Bear

After the EGR try it with the distributor vacuum advance disconnected. If that stops the surge the distributor pole piece wires are failing.

bxd76

I disconnected the EGR hose at the EGR valve and stuck a golf tee into the hose to plug it.

It felt smoother at throttle tip in, and the surge issue was much better.

So I need an EGR valve? I’m sure it’s the original one. I hope the bolts aren’t seized. Will soak them the night before with PB Blaster.

Whats the disadvantage of leaving it unhooked and plugged like this? I drive this car less than 1,000 miles a year.

I’ll have to see tomorrow morning with a cold engine if this fixes the cold start/fast idle stalling issue too.

Thanks for the help!

olds 307 and 403

The stalling is probably choke setting or pull off adjustment related.

gs72

If you are not worried about it being bone stock / correct. Leaving it disconnected will not do any harm. If it runs better, go with it. Agreed You should double check your idle and choke settings for the stalling issue on cold start gear engagement. Also does it stall in reverse engagement or just in drive?

bxd76

It will stall on reverse or drive. I’ve never adjusted a choke before so I’m going to have to learn the process. Thanks!

bxd76

Do you think it’s coming off choke when I put it in gear and leaning out too fast? Maybe I can have someone sit inside the car while I watch it.

If Yes, would I need to loosen the screws on the choke and turn it counter clockwise to richen it?

if I do need to turn it, about how much is a good first adjustment? 1/8 turn? 1/4 turn!

olds 307 and 403

The choke pull off is also adjustable and may need adjusting as well. Check the choke tension when completely cold, resistance depends on temperature. It may need adjustment as well. I have also seen a few failed hot air choke coils apprenticing in a shop and seen plenty of leaking choke pull offs over the years.

bxd76

Trying to learn about chokes and choke pull off adjustment. This video taught me some things. Leaving link here for others who may benefit.

bxd76

After disconnecting the EGR, not only did my surge go away but my stall problem is fixed. I wanted to be absolutely sure of this before I posted so I tested yesterday and today. Both days the car went into drive and reverse and never missed a beat.

I will replace the EGR after the car comes out of winter storage, unfortunately no time right now.

Hope this helps someone else who has a fast idle / cold start stall issue.

Thanks for everyone’s help. I’ll try and update this thread in the spring on whether everything is still good with a new EGR.

rocketraider

Unless you're in an area that requires tailpipe smog testing on a 1978 car, plug the EGR's vacuum source at the valve and disable it permanently. A BB pellet is perfect for this. Push the BB into the vacuum hose and then reconnect the hose to the EGR. It will pass visual.

Provided you can even find an EGR valve or the other components associated with the 1978 engine, breaking the attaching bolts loose after 45 years of hot-cold cycling might be an adventure.

EGR valves and passages get blocked with carbon and soot. They can be cleaned if you can get the valve off. Sometimes that's the problem, sometimes the valve's vacuum diaphram, sometimes the temperature-sensitive vacuum delay valve if it has one.

Dynoking

I would check the EGR thermal vacuum switch (EGR TVS). This is supposed to not allow the EGR valve to open by preventing vacuum flow to the EGR valve until the engine is warmed up. The location of the TVS can be found on the tune up spec label usually located on the radiator support or fan shroud. The TVS can be easy tested with a vacuum gauge connected to the vacuum hose at the EGR valve. If vacuum is present doing cold engine start up the TVS is bad. If you do not have a vacuum gage you can try to feel for vacuum by holding your finger over the end of the vacuum hose, or see if vacuum will hold a small piece of paper to the end of the hose.
If in fact the TVS is stuck open your bigger problem may be finding a replacement. If you want to leave the EGR valve disconnected be aware of ping at part throttle/light loads. Some manufactures added ignition timing to compensate for the effects of EGR.
Please keep us informed of your progress.

bxd76

Hello!



Original poster here with update.



So the 1978 Delta 88 is out of storage and back at home. I noticed on the drive home, that the stumble just off idle is getting worse. Almost felt like it was going to stall out at times. Had to goose it extra to get going from every red light. Once rolling, it seems to have good power, transmission kicks down and car accelerates hard. The idle itself seems good to me too, never a stall or drop in RPM.

It’s just as you dip into the gas pedal off idle it really hesitates and stumbles.



I looked at the EGR hose that I had plugged with a golf tee last fall. Starting at the EGR valve, that hose runs to the area just behind the water pump where it goes into a small black and yellow plastic canister. From that plastic canister the vacuum hose heads up to the carburetor itself, front bottom right port.



The emissions label on the fan shroud does not show where the EGR TVS would be on this car. When I look at rock auto it looks like the switch has two ports on it, but I can’t find it. And the EGR goes to the carb. Any thoughts?



When I started it today, I let it idle for about four minutes. Then I put it into gear and it immediately stalled out. When this happens I immediately restart the engine, put it back in gear and it never stalls the second time!



So I guess unplugging the EGR wasn’t the fix I had previously thought it was.



Those are my only two symptoms.


I found that the coolant temperature sensor was unplugged by accident. But this being a 1978, I assume that doesn’t explain any of my issues? Since there’s really no computer?



Thank you for your patience with me. I’m watching a lot of videos and trying my best to learn. It’s so different than most of my experience with 1990+ fuel injected cars.

Sugar Bear

Could be from sitting, maybe run it low on fuel, fill it with premium and a fuel treatment such as Techron. If you add Techron add 1 ounce per gallon of gasoline, run that tank low before topping it off, otherwise the Techron gets diluted and weaker.

I'd also try revving the fully warmed engine to approx 3k rpm and forcing the choke blade closed and release the choke blade before it stalls. Repeat 3-4 times with the fresh fuel.

Sugar Bear

The disconnected temp sensor isn't related, you are correct. Does it reach full temp 195, degrees?

bxd76

Don’t think it’s from old fuel. Did the same thing last summer after multiple tanks of Shell Premium with Techron concentrate added.

Here’s what I did today:

1. Checked front and rear vacuum break diaphragms. Both hold vacuum.

2. Confirmed I get two solid squirts from the accelerator pump into the carb as soon as I move the throttle. There is no slack or delay in this linkage.

3. Checked my fuel mixture screws. I put my Bosch pressure gauge on the carb’s PCV port which should be manifold pressure. Fully warmed and in Drive, I started with screws at 3 turns out. Was reading about 16. I turned them out one at a time to maximize pressure. I found that one additional turn out got me to about 17. Past that, I turned them a few more turns and it just stayed at 17, engine never started stumbling. How many turns does it usually take to get so rich it stumbles?? Somewhere around 6-7 turns out, with no change happening, I chickened out and went back to around 4-4.5 and left it there.

It was reading about 17 everywhere from around 4-6 turns, but I felt the engine subjectively sounded best around 4-4.5.


I watched a lot of videos online to see what else it could be. I was tempted to try a new cap and rotor next, I think they are very old. But Uncle Tony’s Garage said that a stumble off idle is usually not distributor related because the weights haven’t shifted yet?? Not sure if that’s correct. I’m still tempted to do a cap and rotor. I’m not sure how old they are.

olds 307 and 403

The idle fuel is limited on these carbs, why more turns don't change it much. Check for vacuum leaks and make sure the mechanical and vacuum are both functioning properly.