High RPM's
Thread Starter
Intermediate
Joined: Apr 2022
Posts: 47
Likes: 16
From: Illinois
2022 C3 of the Year Finalist - Unmodified
High RPM's
First, thanks to all that helped me with my leaf spring bushing project. This problem is something that I've had since owning the car. When the AC is on and I come to a stop the RPM's are high and take their sweet time coming down to 900-1000. They're between 1200-1500 when the car initially comes to a stop. i've played with the idle stop solenoid and that doesn't not have an effect on the slow drop. It changes where the RPM's start, but then there is the slow drop. If I set it to start at the 900-1000 mark, they drop is down to as low as 500 and the car stalls. So, I've set it to where it's at the 1200+ mark and it will eventually drop to 800. This happens with the AC off, but it's not as dramatic. With the AC off, the RPM's might be 1100-1200 but come down to 900. It's not instant, but it's a lot quicker than when the AC is on. Any ideas what is causing this?
Race Director
Joined: May 2006
Posts: 18,743
Likes: 2,585
Have you tried setting it based on the instructions on your emissions decal? As an example a 1978 L82 with automatic you set the solenoid to 750 in Drive with AC on. You then turn the AC off and set the idle speed screw to 700 in Drive. Then you adjust the mixture screws and recheck rpm settings.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Where is your timing set at?
Long time to come back to idle is almost always a vacuum leak........get an unlit propane torch and "sniff" all around the intake and carb.....as well as vacuum hoses for headlights......notice if the idle changes....
Jebby
Long time to come back to idle is almost always a vacuum leak........get an unlit propane torch and "sniff" all around the intake and carb.....as well as vacuum hoses for headlights......notice if the idle changes....
Jebby
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Kid Again,
You need to isolate the carb from another possible source, to verify it truly is the carb.
Unhook the throttle cable and bracket at the carb. Start it up. Act the same? Or did it improve? How are the return springs?
While the cable is still detached, hold it straight up in the air. Apply a little of your favorite lube and work the cable inside the sheath. You should hear the gas pedal moving. No binding.
You need to isolate the carb from another possible source, to verify it truly is the carb.
Unhook the throttle cable and bracket at the carb. Start it up. Act the same? Or did it improve? How are the return springs?
While the cable is still detached, hold it straight up in the air. Apply a little of your favorite lube and work the cable inside the sheath. You should hear the gas pedal moving. No binding.
Thread Starter
Intermediate
Joined: Apr 2022
Posts: 47
Likes: 16
From: Illinois
2022 C3 of the Year Finalist - Unmodified
@MelWff thanks, but I wouldn't even know where to look for that. Also, it runs really well with the carb set where it is, so I don't want to mess with the mixture screws anymore. I'm going to try some other suggestions and see what happens.
Thread Starter
Intermediate
Joined: Apr 2022
Posts: 47
Likes: 16
From: Illinois
2022 C3 of the Year Finalist - Unmodified
@Jebbysan Thanks. I know I have a leak as the lights don't go up together. I've seen that method posted before so I'm going to give it a shot. As for the timing, I don't have a clue. I've had 2 mechanics in 2 years of ownership work on it and neither brought the time up in conversation or billing. The first one missed installing the solenoid and second messed with the carb "to improve it" and I ended up redoing the fast idle screw, choke, fuel mixture screws and solenoid to get it running better than either of them with the exception of the revs coming down slowly. Hopefully your suggestion will work.
Thread Starter
Intermediate
Joined: Apr 2022
Posts: 47
Likes: 16
From: Illinois
2022 C3 of the Year Finalist - Unmodified
@HeadsU.P. Thanks. I've considered getting new springs as someone else mentioned that to me too. I never considered lubricating the cable, but will look into it as well.
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