Hey everyone! Well its been a busty 3 months. After taking the upper half of the 350 apart installing new cam, water pump, belts, fan clutch and some other things the Buick is running great. However Im having an idle issue. Ill go driving and after maybe 5-10 miles when I come to a stop I notice the idle has gone up by about 200-300 causing me to be at like 900/1000rpm idle while in drive and stoped. I have adjust idle screw but that doesn't seem to fix it. Are there some other tests i can run to diagnose? Thank you in advance for any help. Eric
Should be able to lower the idle with the idle screw. You're not adjusting the fast idle screw by mistake?
It could be a small solenoid that is at the end of the throttle lever. It is just a plunger with a spring on it and it was supposed to let your idle come down slow in case you have the air conditioner on and you stab the gas and let off quickly. It was on my 71 350 2bbl with air. There is no electric to this part it is just operated by a spring and a plunger
In 1972, it was an electrical solenoid. Buick called it an idle stop solenoid. It prevented run on. It had nothing to do with the A/C. The plunger extended with the ignition on, and set the curb idle speed. The plunger was adjusted with an open end wrench, it screwed in and out. There was a slow idle speed adjusting screw. Adjustment was as follows. Pull electrical connector off solenoid. Adjust idle IN DRIVE to 500 RPM with idle speed screw. Reconnect solenoid, and extend plunger. Adjust idle speed via the solenoid plunger IN DRIVE to 650 RPM. No, that's a dashpot. Not on 72
no its the idle adj screw, and ill adjust it but it still seems to move up. i dont even have the idle stop solenoid hooked up, so thats not making it change.
Could be the weights in the distributor is sticking causing advance to to be higher at idle which would make your idle go up. Could be weak springs or just worn out and sticking. The small rods that hold the weights can get worn down. Yes Dashpot was the name I was looking for. When the air conditioner was on this did help to keep the engine from stalling if you stepped on the gas and let off quick. Worked good for a couple of years then it started to stick and keep the idle up too much, I had to take it off.
I added new springs to distributor. Only seems to happen after it’s warmed up, and I have gone for a drive. I set idle when engine was at temp and warm. However it still seems to be off a little. Could also be a 50 year old carb that hasn’t been tuned properly.
If the springs are too light, they add timing at idle. That can cause an increase in idle speed when the engine warms up. It is also possible that the throttle blades are sticking a little. Next time the idle speed is higher, grab a hold of the throttle arm and try to close the throttle. See if that works.
Let it run for about 30 mins and adjusted screw a little more. Think i got it dialed in. It was super touchy, 1/13 of a spin made about a 100rpm difference so I adjusted and let sit, reved up, put into gear (idle was 500/550) back to park 700/800. Did that a few times, also tuned off let sit, then turned over and made sure adjustments hold. So far seems to fix it. Didn’t realize how sensitive the adjustment screw was.
Its normal. Your trying to adjust idle speed on a "just" warm engine, its NOT hot as it should be like after driving, thats why your having this issue. My GS does the same thing if I try adjusting the idle without the engine being fully heated(after driving it like 20/30 miles), I'll adjust the idle to 700/800 in gear. go for a long ride (to work) and the idle is 100 to 200 RPM higher. Adjust it after driving and the engine is hot Same thing happens when you cold start a carb'd car on a winter morning, the car starts on fast idle, but after the oil warms, parts warm up, the fast idle gets REALLY fast after a few minutes.
You may also look for vacuum leaks. Spray carb cleaner around the base of the carb and where the manifold meets the heads to see if the idle changes. Unplug the vacuum line to the brake booster and block it off, if the problem goes away, your booster has a leak. Look for broken vacuum lines going to accessories.
If the carb has been taken off recently you could have overtightened it and this can cause the blades to stick open slightly. Adjustment screws are very sensitive, I spend a good half hr adjusting my Holley using a big rpm scale and a vac gauge to monitor both.
