Engine idle speed increases with temp. And whistling

[Redsquall]

Dmcmidwest got the car tuned and running well. CO, oxygen sensor, timing, all tuned. The next thing is the idle starts around 750 cold and goes up to around 1400 after about 10 minutes. Throttle not sticking. Also seems to whistle a lot. Ideas? Thanks guys

[Jonathan]

That might not be a sticking throttle, but the symptoms sound the same. It could be that once your engine warms up, it pulls a stronger vacuum and is lifting the butterfly valves off their seal.

There could be a couple things to correct that:

If the butterfly valves are not going back to a good zero position under no throttle, it might mean the lever arm isn't returning all the way. It might still be contacting the idle microswitch with the top post, but the bottom post might be keeping it out too far mechanically and the inside portion of that intake pipe is seeing the valves stay slightly open. This would get magnified once warm if the stronger vacuum is overcoming the strength of your lever arm return spring. You can lube that lever arm spring or take it all apart and ensure it isn't getting caught up on itself from grime or whatever.

The other option is that the idle microswitch is getting engaged initially, but once warm, that same strong vacuum is overcoming the return spring and lifting the post off the switch. Test that by pushing in on the switch with the tip of a pen. You can test it also by pushing the whole lever arm in farther, but that captures both of these two possibilities and you'll want to try and figure out if it's one versus the other.

In any event, it sounds to me like it's a throttle spool assembly adjustment issue, combined with a weak or dirty return spring. Any of that is not hard to correct thankfully.

[Redsquall]

Thanks again jonathan - I'll check this out and respond with findings if it helps someone else...



That might not be a sticking throttle, but the symptoms sound the same. It could be that once your engine warms up, it pulls a stronger vacuum and is lifting the butterfly valves off their seal.

There could be a couple things to correct that:

If the butterfly valves are not going back to a good zero position under no throttle, it might mean the lever arm isn't returning all the way. It might still be contacting the idle microswitch with the top post, but the bottom post might be keeping it out too far mechanically and the inside portion of that intake pipe is seeing the valves stay slightly open. This would get magnified once warm if the stronger vacuum is overcoming the strength of your lever arm return spring. You can lube that lever arm spring or take it all apart and ensure it isn't getting caught up on itself from grime or whatever.

The other option is that the idle microswitch is getting engaged initially, but once warm, that same strong vacuum is overcoming the return spring and lifting the post off the switch. Test that by pushing in on the switch with the tip of a pen. You can test it also by pushing the whole lever arm in farther, but that captures both of these two possibilities and you'll want to try and figure out if it's one versus the other.

In any event, it sounds to me like it's a throttle spool assembly adjustment issue, combined with a weak or dirty return spring. Any of that is not hard to correct thankfully.

[DMCMW Dave]

Whistling is usually a true vacuum leak, usually at the W-pipe just over the thermostat. Either the paper gaskets or even one of the O-rings. Will cause a very high idle too.

[Redsquall]

Jonathan, it is indeed the microswitch – at least part of it. I'm going to put my new micro switch on because after I just of this old one the next day it looks like The switch is not engaging again and needs further adjustment – so I might as will put my new one on.





That might not be a sticking throttle, but the symptoms sound the same. It could be that once your engine warms up, it pulls a stronger vacuum and is lifting the butterfly valves off their seal.

There could be a couple things to correct that:

If the butterfly valves are not going back to a good zero position under no throttle, it might mean the lever arm isn't returning all the way. It might still be contacting the idle microswitch with the top post, but the bottom post might be keeping it out too far mechanically and the inside portion of that intake pipe is seeing the valves stay slightly open. This would get magnified once warm if the stronger vacuum is overcoming the strength of your lever arm return spring. You can lube that lever arm spring or take it all apart and ensure it isn't getting caught up on itself from grime or whatever.

The other option is that the idle microswitch is getting engaged initially, but once warm, that same strong vacuum is overcoming the return spring and lifting the post off the switch. Test that by pushing in on the switch with the tip of a pen. You can test it also by pushing the whole lever arm in farther, but that captures both of these two possibilities and you'll want to try and figure out if it's one versus the other.

In any event, it sounds to me like it's a throttle spool assembly adjustment issue, combined with a weak or dirty return spring. Any of that is not hard to correct thankfully.

[Redsquall]

So the microswitch solve the high idle problem but there is still some whistling here and there. I sprayed starter fluid around the W pipe with no change in RPMs. Is there a better way to look for the leak without a smoke machine? Thank you Dave



Whistling is usually a true vacuum leak, usually at the W-pipe just over the thermostat. Either the paper gaskets or even one of the O-rings. Will cause a very high idle too.

[FABombjoy]

Stick a length of tube in your ear and use the free end to pinpoint the source.

If the W-pipe is suspect, lightly tighten bolts while running and listen for changes. My money is on the bolt holding the splash shield in place.

[David T]

Vacuum leaks are sneaky. I have seen where the "O" rings and or the spacers are missing or mis-positioned on the throttle body. Gaskets torn or missing. Broken bolts glued in place or just left out. One really sneaky one was someone used too long a bolt on the end of the intake manifold for a ground and bent the freeze-out plug on the end. Very common for the injector seals to get old and hard and start leaking. On one car the "O" ring on the cold start valve was missing. The "O" ring on the air pipe under the mixture unit is a regular favorite. Often there is no plug or seal over the mixture screw. Each vacuum leak is cumulative and they all add up to one BIG one. Each one reduces the power of the idle motor to control air and it's ability to control the idle. They also lean the A/F ratio since the air senor plate is not measuring the airflow and adding fuel to the air leaking in. The Lambda system can't make up for it either. The K-Jet system depends on a tight system (no vacuum leaks) or it cannot run right. No amount of tweaking or adjusting will help. Of all the methods I have tried, a hose to listen for leaks, using Propane to make the engine run faster when you put some near suspected leaks, and others, the only one that works and is easy is to use a smoke machine. It makes the invisible visible! It is fast, safe, and clean. The only draw-back is you need a smoke machine!