Backpressure on throttle lever at idle

[Fox2506]

I've already posted a similar topic on DMC Help, fyi.

I've been having trouble getting my car to idle properly. When, and only when, the engine is warm or hot, the throttle does not return all the way to the microswitch. Sometimes, I can tap the pedal and it will go down. But when the engine is hot/running, it will never go down, and when I push on it with my finger it is quite resistant. The second I turn the engine off, it returns to home position. Is this back-pressure normal?

The butterfly assy is new.

This issue was present in my last engine. I have had a crate stage II for over a year now, and the problem has resurfaced. Some parts such as the microswitch and idle motor were recycled from the old engine.

[David T]

You probably have play in the ends of the quadrant link. Adjust it so it forces the throttle arm all the way to idle.
David Teitelbaum

[jmettee]

You mean like this?

http://www.youtube.com/watch?v=1OwRpTlfZoQ

Basically, you need to do 2 things.
1) Take apart the throttle spool, clean the bearing surface (the bearing is a plastic flange bearing) & also the ball-sockets on the rod going from the spool to the butterfly linkage. After cleaning, apply a light film of light oil (or dry graphite) to the spool & bearing grease to the ball sockets.

2) Adjust the throttle settings.

I start at the butterfly linkage by backing out the stop butterfly stop screw. I adjust the stop position while feeling the butterfly as I move it back & forth. Without the stop screw functioning, you will feel a stickiness when the butterfly first starts to open. You want to adjust the stop screw just enough until that stickiness goes away, then add 1/4 turn & lock down the jam nut.
Next, back out the microswitch screw to reset it. With the throttle all the way closed, slowly screw it in just until the microswitch clicks. Then screw in further 2.5 turns, & lock the jam nut.
Next, move to the spool. With a 2nd person, adjust the cable position such that the spool contacts & engages the full-throttle switch while your helper is pressing the gas pedal all the way to the floor.
Finally, with the 2 "ends" set, adjust the rod linkage between the butterfly link & the spool such that the spool springs are helping the butterfly springs close (i.e. there should be slight tension on the rod). Without the rod & spool pulling on the butterfly lever, there is a tendency for the butterfly to stick open & cause high idle unless the gas pedal is "snapped" to have it close all the way for proper idle.


As you see in the video, I was having this issue a couple years ago. I decided to start fresh & adjust everything & it worked.

[Fox2506]

Thanks for the info. I do know that procedure by heart.

I ran through the procedure and my throttle stop screw was backed out to the end. I'm sure that was causing the butterfly plates to stick inside the ports. So I turned the screw only about 2 to 4 turns and then set the microswitch screw.

I started the car and it had enough power at idle to move without hitting the gas.

When I tapped the microswitch, nothing happened. When I unplugged the idle motor with the switch engaged, nothing happened (at the previous screw setting, unplugging the idle motor would drop the RPM). I was forced to set the screw back to where I had it.

I am guessing the only reason I am getting a decent idle currently is because I am allowing the butterfly to close more than a healthier idle system would need. Yet that is causing the poor lever return.

I guess it is the microswitch, like I've been told several times. I'm too stubborn. Anymore thoughts?

[jmettee]

You can easily determine if it's the microswitch or not. Unplug the 2 spade connectors from the back of it. At idle, I believe you should have a high idle with them disconnected & if you short them together, your idle should drop (or I may have it backward). This would mean the switch is bad. If nothing happens, you either have a bad connection, broken wire, or some other anomaly in the circuitry.....a stuck or bad idle motor or connection to it....or your idle ECU has an issue. or is toast.

[Fox2506]

I repeated the process again with the engine on and got it idling at 1000 RPM consistently. Steve W. told me that Stage II's should idle closer to that range than 750 anyway, I believe. But when I turned the car on moments later, the rpm was stuck near 2000...

Is John Hervey's microswitch a sufficient replacement?

[DMCMW Dave]

2524 Good

2525 Bad

Take the W pipe off the back of the engine and open the throttle wide. If the decel valve springs appear collapsed in the center you need to replace the throttle body. I've seen this a few times, and when I have an engine where the idle speed won't set down this is always the problem.

I've never really figured out what causes this, no particular VIN sequence etc. But it will fix the problem if your springs look like the picture on the right.

I've heard tell of soldering the valves closed, but that will cause stalling issues.

[Fox2506]

That's also good to know, as I wondered about that. But I pulled out my old mixture control unit and butterfly, and the springs were in perfect condition. The new engine is only one year old, so I doubt those springs are bad either. Maybe I'll pull it apart later. My point is that this problem is EXACTLY the same as what I was dealing with before the crate motor.

Frankly, I'm down to
-microswitch
-idle motor (unplugged with MS tripped = nothing. unplugged with MS untripped = RPM drop)
-ECU

Thanks for the input guys

[DMCMW Dave]

With the engine running pull the connector off the idle ECU that's closest to the center of the car. Idle should take off to 2200 rpm and settle back down immediately when you plug it back in. If not, the ECU is bad or the motor is stuck/sticky. Or bad.


At any rate, this is a good fast test of the idle motor and ECU as to basic function.

[Fox2506]

Started the car and it ran at about 800 RPM and sounded alright.

Unplugged the center-most connector on the computer and the RPM shot up to about 2900 (or so the tach showed).

Plugged it back in, RPM went to 1200 with frequency valve active for about 10 seconds, and noticed a rich exhaust smell.

Though the throttle had never been touched, I pressed it down firmly. When I let go and stepped away, the idle would be at 1000 for a couple of seconds and then 1200 for several seconds back and forth. This repeated continuously as I stood back. I didn't hear any clicks or frequency valve action during the fluctuation--just up and down idle.

[Bitsyncmaster]

The idle system is set to 775 RPM. If you adjust the curb idle screw or open the bypass screws to increase the idle higher than 775 then the idle motor will stay closed (almost) and not have anything to do with idle speed.

[jmettee]

With the engine running pull the connector off the idle ECU that's closest to the center of the car. Idle should take off to 2200 rpm and settle back down immediately when you plug it back in. If not, the ECU is bad or the motor is stuck/sticky. Or bad.


At any rate, this is a good fast test of the idle motor and ECU as to basic function.

Dave, similarly, would unplugging the O2 sensor throw the ECU into default state & prove that it's functional in another way....or does this prove exactly the same thing as unplugging the ECU? (I know uplugging the ECU can smooth out a hunting condition).

[DMCMW Dave]

Disconnecting the O2 sensor goes to open loop, if reading with a dwell meter you see 45 degrees.

If you ground the O2 sensor lead going to the ECU it will go full rich (85 degrees) and if you put a 1.5 V flashlight battery with the + to the ECU and the - to ground it will go to full lean (typically about 18 degrees). This test is actually in the manual at the very end of the fuel injection writeup. If it passes this test the ECU is working. You will hear changes in engine tone as you hit the extremes (you can do this test by jumpering the RPM relay with the engine off and you can hear the frequency valve change tune.

[jmettee]

Disconnecting the O2 sensor goes to open loop, if reading with a dwell meter you see 45 degrees.

If you ground the O2 sensor lead going to the ECU it will go full rich (85 degrees) and if you put a 1.5 V flashlight battery with the + to the ECU and the - to ground it will go to full lean (typically about 18 degrees). This test is actually in the manual at the very end of the fuel injection writeup. If it passes this test the ECU is working. You will hear changes in engine tone as you hit the extremes (you can do this test by jumpering the RPM relay with the engine off and you can hear the frequency valve change tune.

That's what I thought, but I'm away from home (& my shop manual). Just trying to get some easy tests so he can prove his ECU is working or not.

[Fox2506]

Ever since unplugging the ECU, I've been getting a lot of rich exhaust fumes.

[Bitsyncmaster]

Which ECU are we taking about here? I thought we were checking the idle ECU and then we got into the O2 sensor.

[Fox2506]

Just an update. I confirmed that my microswitch is bad. I was told that the microswitches should remain grounded even when fully depressed. Mine is only grounded when pressed to the point when it clicks.

[tonslawed]

Maybe that's how problems will start.

[kings1527]

2524 Good

2525 Bad

Take the W pipe off the back of the engine and open the throttle wide. If the decel valve springs appear collapsed in the center you need to replace the throttle body. I've seen this a few times, and when I have an engine where the idle speed won't set down this is always the problem.

I've never really figured out what causes this, no particular VIN sequence etc. But it will fix the problem if your springs look like the picture on the right.

I've heard tell of soldering the valves closed, but that will cause stalling issues.

Hi Dave,

I think I might be having a problem with my decel springs. And thanks for the pics you provided. Here are mine:

150511505215053

I'm currently stuck at an idle at around 1000-1100 when warmed up to operating temp, and about 775 on the money during first start-up. What's your best opinion? I feel like I've ruled out just about everything else (at least with my knowledge base). Thanks again for all your help.

Alex
6575

[DMCMW Dave]

Definitely bad.

[Elvis]

The weekly idle thread :-)


Alex - you say when the engine is warmed up the idle goes up ?
when you turn it off and back on without touching the pedal - will it immediately
go up again or stay at 775 rpm ?

You did you make sure the idle motor is working properly, right ?

[kings1527]

The weekly idle thread :-)


Alex - you say when the engine is warmed up the idle goes up ?
when you turn it off and back on without touching the pedal - will it immediately
go up again or stay at 775 rpm ?

You did you make sure the idle motor is working properly, right ?

Hi Elvis. Yes, I know you've had quite a hand in fixing awnry idles!

Yes, the idle will go up once the oil gets heated up. I'll start at 775 and go up to about 1000 when it's at operating temperature. When I turn it off and then back on, I want to say it goes right back to where it left off. I'll have to double check on that. I did adjust the throttle linkage so it pushes the butterfly valves closed all the way.

As far as the idle motor goes, I'm going to clean it when I get back from my trip this week. I'll flush it with some electrical connection cleaner to make sure everything is ok with it. But I haven't taken it out and twisted it fast to make sure it's free inside.

Alex
6575

[Bitsyncmaster]

Those springs look just like my bad springs. I had the same problem, 1000 RPM after it warmed up even with the curb idle screw fully backed out.

[kings1527]

Those springs look just like my bad springs. I had the same problem, 1000 RPM after it warmed up even with the curb idle screw fully backed out.

Thanks Dave. I know we touched on this a few months ago but I've had all kinds of projects going on with the car. I shouldve followed your advice a long time ago!

It'll be a good time to get a new throttle body anyway. The PO broke off one of the brass screws so it'll be nice having it look normal again.

Alex
6575

[Elvis]

All I want you is to push the butterflys to fully close when the idle is high again.
When the idle goes down it's the shaft / vacuum problem that I seem to be only
one worldwide who has seen this on 3 cars so far (3 cars I worked on).



How to electrically test the idle motor has also been described so often that I don't
want to repeat it anymore.

[Bitsyncmaster]

Thanks Dave. I know we touched on this a few months ago but I've had all kinds of projects going on with the car. I shouldve followed your advice a long time ago!

It'll be a good time to get a new throttle body anyway. The PO broke off one of the brass screws so it'll be nice having it look normal again.

Alex
6575

Don't think a new throttle body would have the brass screws included. A used one may have them.

[mluder]

Don't think a new throttle body would have the brass screws included. A used one may have them.

It doesn't... I ordered one as well to hopefully correct the same problem though I haven't had a chance to install it yet. I'll be curious to see if it solves the problem here.

FYI - Also ordered the brass screwas though they only have one type available now.

Interrestingly the lever on my throtle assembly (which attaches to the the throtle arm) has a bend in it. It appears intentional. Does anyone know if there were different versions of this assembly?

Cheers
Steve