Idle not coming down after rev

[alexwolf1216]

Hi everyone. I just completed my VOD journey, and i was just about to take it for a drive when I noticed some odd behavior.

When I start the car, the idle is fine. It sits right at 775 like its supposed to, but after I rev it sits at 1750ish. No matter what i do I cant get it to come back down. If I turn off the car and restart, idle is fine. To me this rules out the throttle cable, but I could be wrong. What could be causing this?

[alexwolf1216]

http://youtu.be/9IDsLgEXOGQ

[dn010]

Start the car and go to the engine, manually push on the throttle spool to see what is going on, could be an issue with the spool/cable binding or it could be your idle speed motor.

[alexwolf1216]

So why would it start normally each time if it was the throttle spool?

[alexwolf1216]

The pool returns to 0 each timr

[dn010]

I mention the spool so you can rule it out and also see if everything else linkage related is working properly. Otherwise start going over your electrical connections and also check out your idle speed motor.


So why would it start normally each time if it was the throttle spool?

[hmcelraft]

Have you checked to see if the fuel injection throttle plate is sticking. I noticed the 1500RPM idle was not smooth which made me think that it might be open and not in it's rest position. When you turn off the fuel pump the lower pressure would allow it to go back to rest.

[sdg3205]

the engine running vacuum is enough to keep mechanicals from fully closing. It's kind of like starting friction - once the've moved with a blip of the throttle, the game changes.

Taking all the junk apart moves everything out of spec. Sounds like the microswitch isnt being engaged.

[DMCMW Dave]

If all else fails, and you can't push the linkage and have is slow down, it's likely the decel valves are sticking open. When you shut the engine off they will close, but the first time you slam the throttle shut while running they will pop open and stay there. The springs fail and get very weak.

It's covered on a few other threads on the forum.

Exhaust other possibilities first as you have to take stuff apart to prove this is the problem.

[Soundkillr]

I second vote for micro switch. When mine when bad I had fluctuating idle, and it would be fine a start up and after a few minutes would be higher thank normal.

[ALEXAKOS]

if it is the micro switch its easy to see if faulty.
Simply push it down with a screwdriver until it clicks. Then you will know.

I got the same problem.
Dave is right.
The return spring does not help the butterflies to shut 100%
What I did is extend the connection from the spool to the butterflies spring. That solved my problem.
Also lube up the joint of the spring so you feel it snap back tensely. Make sure the lube is not going to make things worse later in time like get hard or sticky.
Vaseline is always a good lube :)

[dn010]

if it is the micro switch its easy to see if faulty.
Simply push it down with a screwdriver until it clicks. Then you will know.

I got the same problem.
Dave is right.
The return spring does not help the butterflies to shut 100%
What I did is extend the connection from the spool to the butterflies spring. That solved my problem.
Also lube up the joint of the spring so you feel it snap back tensely. Make sure the lube is not going to make things worse later in time like get hard or sticky.
Vaseline is always a good lube :)

Mine would never work properly, I ended up having to put a heavy spring from the spool to the back closing panel in order to get it to return/close all the way (Back when I had the original PRV).

[DMCMW Dave]

If you adjust the preload on the link from the spool to the throttle arm you can make that spring help push the throttle closed.

[David T]

If you adjust the preload on the link from the spool to the throttle arm you can make that spring help push the throttle closed.

In a lot of cases you have to go over the whole throttle system meaning:
Lubricate the throttle cable as per SC-01-1/82
Disassemble. clean, lubricate and reassemble the throttle spool
Lubricate and adjust the quadrant link
After 30 years the original lubricant gets dried up and gummy preventing the springs from being able to work properly. Adding more spring is not the answer. On a long drive it can get tiring on the foot. The buttterfly assembly also has a spring in it (besides the springs on the decel valves). After getting everything to work easily and smoothly recheck the adjustments on the throttle stop and micro switch. All too often when there is a problem the FIRST thing some people do is start cranking on anything they can find to adjust. Most of the time that is the exact WRONG thing to do. The adjustments don't change, trying to "adjust" a problem away seldom works but in the process you lose all of the correct adjustments and if you don't know how to set them properly you lost it.

[DMCMW Dave]

In this case the car was running normally until he took the intake off for other maintenance. Now it isn't. There are quite a few parts related to the throttle that go back together "approximately" where they were.

So it needs adjustments to put it back "right". There are many adjustments in the throttle linkage:
--Basic shape of the gas pedal linkage inside the car
--adjustment at the cable end at the throttle bracket
--spring tension on the spool
--adjustment at both ends of the linkage rod
--adjustment on the stop screws for the base idle AND the micro switch

As David T mentions, lots of friction points too. Including one under the bracket where the linkage rod can drag on the bottom of the bracket if you had to force the bracket into position.

[Jonathan]

Here's the decal valves Dave mentioned to give you a visual:

http://dmctalk.org/showthread.php?10336-Assorted-helpful-technical-photos&p=152181&viewfull=1#post152181

Try the test of pushing the lever arm into the idle micro switch and see if that changes your idle or not. Or whether the spool is coming back to where it should be even without actually getting to touch the micro switch. A helped working the pedal while you watch from the engine bay is good.

Also Alex, what's the story with your oil pressure gauge being pegged straight up? And does your battery warning light come on solid when you turn the key to accessories before you start the engine? From your video, it looked like it came on later than I would have expected. Maybe that's related to a different alternator? I don't know about that as I don't have one of those replacement ones that makes the batter light strobe when it's on.

[David T]

if it is the micro switch its easy to see if faulty.
Simply push it down with a screwdriver until it clicks. Then you will know.

I got the same problem.
Dave is right.
The return spring does not help the butterflies to shut 100%
What I did is extend the connection from the spool to the butterflies spring. That solved my problem.
Also lube up the joint of the spring so you feel it snap back tensely. Make sure the lube is not going to make things worse later in time like get hard or sticky.
Vaseline is always a good lube :)

Not in automotive applications. When it gets warm it will just turn into water and run right out leaving a congealed mess. Use something better. Good grease is not expensive and you can buy a small can of it in an auto store.

[alexwolf1216]

It was totally the microswitch. The throttle plate that screws into the top of the thermostat didn't fit on the new water pump so we had to bend a little bit. When we did, we had to adjust the linkage arm and put it one turn too much.

Something still isn't quite right, it idle searches at startup for a few minutes ten settles down, but still isn't idling perfect. I looked for vacuum leaks using the carb cleaner trick but didn't get any result.

[David T]

It was totally the microswitch. The throttle plate that screws into the top of the thermostat didn't fit on the new water pump so we had to bend a little bit. When we did, we had to adjust the linkage arm and put it one turn too much.

Something still isn't quite right, it idle searches at startup for a few minutes ten settles down, but still isn't idling perfect. I looked for vacuum leaks using the carb cleaner trick but didn't get any result.

An unstable idle for a couple of minutes right after start up is "normal". It can be a sign of the CPR out of calibration, worn ignition parts, etc. If it stabilizes quickly with no stumble or other symptoms leave it alone.

[DMCMW Dave]

An unstable idle for a couple of minutes right after start up is "normal". It can be a sign of the CPR out of calibration, worn ignition parts, etc. ...........

Or just being set a tad lean.

[Ron]

For prosperity...
If you have tried the above and still have this problem (especially if it does this >40C (104F)), check that the vacuum lines to the solenoid valve are not reversed. [The solenoid will not vent properly causing it to apply vacuum to the distributor's timing advance mechanism at idle, until you shut the engine off...]

[alexwolf1216]

Also Alex, what's the story with your oil pressure gauge being pegged straight up? And does your battery warning light come on solid when you turn the key to accessories before you start the engine? From your video, it looked like it came on later than I would have expected. Maybe that's related to a different alternator? I don't know about that as I don't have one of those replacement ones that makes the batter light strobe when it's on.

Sorry, I missed this. The oil pressure pegged issue is new. I replaced the pressure sender on the passenger side of the engine with the recommended replacement part, and replaced the copper crush on the sensor on the other side. I also heat shrinked the little wire, and thats when this all started.

I also have a brand new DMC alternator. Something is a little finicky because the clock flickers at startup. I havent gotten to diagnose it, but its on my list somewhere.

[alexwolf1216]

Video of the idle surge

http://youtu.be/CDy_KIm8BWI


http://youtu.be/CDy_KIm8BWI

[Elvis]

nice idle, and of course holding your thumb on a hose to the crankcase will change it LOL


what have you read so far about reasons for hunting idle ?

vacuum leaks ? yes right.

and the other way around ? mixture too rich ?

how to measure the pulse width of the frequency valve ?
and reasons why the mixture is too rich ?

CPR out of calibration ? or not powered by the RPM relay ?

maybe the RPM relay failing because of broken solder joints like
sooner or later ALL of the original RPM relays have ?
(use a solder tool and fix it in 2 minutes)


Every few days the same idle problems here, somebody should
write a how to guide :-)

[alexwolf1216]

nice idle, and of course holding your thumb on a hose to the crankcase will change it LOL


what have you read so far about reasons for hunting idle ?

vacuum leaks ? yes right.

and the other way around ? mixture too rich ?

how to measure the pulse width of the frequency valve ?
and reasons why the mixture is too rich ?

CPR out of calibration ? or not powered by the RPM relay ?

maybe the RPM relay failing because of broken solder joints like
sooner or later ALL of the original RPM relays have ?
(use a solder tool and fix it in 2 minutes)


Every few days the same idle problems here, somebody should
write a how to guide :-)

You know, I am not sure why you feel the need to be so condescending. This is the first car I have ever worked on myself, and yes, I am aware some of my questions are really elementary. I read every single post every day trying to learn as much as I can. I know how to use the search feature, and I regularly speak with my choice of vendor to get a little guidance. This problem is brand new, it never did this before I went into my valley. Yes, I am at a loss and unsure what to do next, but please, if you want to talk down to me because I dont have the in depth knowledge that you do, just keep it to yourself. I dont give two rats shits about what you or anyone else thinks of me. I am here and making progress due to the helpful people on this group, and its the only reason my car is even running.

Thanks again for your super helpful reply.

[Elvis]

I am not condescending, but I'm trying to push people to use the search function
to test things that are being posted over and over again every few days.


Did you open the RPM relay yet ?

A simple and quick task to do, this may solve your problem and may prevent
your from calling AAA.

[alexwolf1216]

My rpm is dave's solid state.

[Jonathan]

I think you got it exactly right, Alex. The part about Elvis talking down to you or sounding condescending. And definitely you got it right about not giving two shits about what he thinks of you. I rarely ever read a post by Elvis where he doesn't come across as a prick, so don't feel like you're being targeted specifically. He feels the need to do this to everyone for some reason.