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914World.com _ 914World Garage _ RPMs very slow to drop
Posted by: Tdskip Oct 16 2018, 03:40 PM
Hi guys-hoping to get some sage advice here on what's going on. I am picking at the 1973 1.7 L D-jet car and when I was test driving her today she did not want to return back to idle.
When you accelerate in first gear up to about 3500 or 4000 RPM and then take your foot off the gas the RPMs stay at the same level or climb slightly and then only slowly drift down.
She starts fine and will idle at about 1000 RPM, air bleed screw is close to all the way in.
There is an aftermarket return spring on the throttle assembly but appears to have the right amount of tension. I took the air cleaner off and when I manually actually the throttle it appears to settle down faster than when I do it with the gas pedal.
The pedal does not appear to be binding on the carpet or interior trim.
Any ideas for me?
Thanks!
Posted by: 76-914 Oct 16 2018, 03:56 PM
Hi guys-hoping to get some sage advice here on what's going on. I am picking at the 1973 1.7 L D-jet car and when I was test driving her today she did not want to return back to idle.
When you accelerate in first gear up to about 3500 or 4000 RPM and then take your foot off the gas the RPMs stay at the same level or climb slightly and then only slowly drift down.
She starts fine and will idle at about 1000 RPM, air bleed screw is close to all the way in.
There is an aftermarket return spring on the throttle assembly but appears to have the right amount of tension. I took the air cleaner off and when I manually actually the throttle it appears to settle down faster than when I do it with the gas pedal.
The pedal does not appear to be binding on the carpet or interior trim.
Any ideas for me?
Thanks!
You stated that it returned to idle more quickly when you operated the throttle by hand. What happens when you disconnect the cable from the throttle body?
Posted by: EdwardBlume Oct 16 2018, 03:58 PM
Is the accelerator pedal returning easily? Does it hang up on anything when you test it from the engine side in neutral with the parking brake on?
Posted by: andreic Oct 16 2018, 04:35 PM
1) You must be having some pretty bad leaks if you can not bring the idle down with the screw on the throttle. Replace all vacuum lines and/or test with a carb cleaner spray at all connections.
2) If the problem is not mechanical (throttle plate not returning to idle position by itself) you may also have a problem with the distributor timing advance. One of the two vacuum lines from the throttle body goes to the distributor in order to retard the timing at idle -- this lowers the idle RPM for emissions control. If the advance plate in the distributor sticks, or the canister does not hold a vacuum, it may be slow to retard the timing, so the idle is slow to come down.
Posted by: forrestkhaag Oct 16 2018, 04:57 PM
CARBS..... 
Posted by: adolimpio Oct 16 2018, 07:15 PM
Cable binding?
Posted by: Dave_Darling Oct 16 2018, 08:22 PM
Suspects:
- Air leaks. This includes the possibility that the throttle plate isn't closing correctly. Or that the decel valve is hanging open. Or some other air leak.
- Timing. Advanced timing will raise your idle; if the timing sticks advanced it will keep the RPMs up, then when the timing drops so will the RPMs.
--DD
Posted by: black73 Oct 17 2018, 04:53 AM
Worn throttle cable.
Posted by: jim_hoyland Oct 17 2018, 05:10 AM
Just went through the same thing; I dry-lubed the moving parts on the TB and the accelerator part of the pedal cluster. Seems like I have to do this about once a year.
Posted by: 914_teener Oct 17 2018, 01:15 PM
Hi guys-hoping to get some sage advice here on what's going on. I am picking at the 1973 1.7 L D-jet car and when I was test driving her today she did not want to return back to idle.
When you accelerate in first gear up to about 3500 or 4000 RPM and then take your foot off the gas the RPMs stay at the same level or climb slightly and then only slowly drift down.
She starts fine and will idle at about 1000 RPM, air bleed screw is close to all the way in.
There is an aftermarket return spring on the throttle assembly but appears to have the right amount of tension. I took the air cleaner off and when I manually actually the throttle it appears to settle down faster than when I do it with the gas pedal.
The pedal does not appear to be binding on the carpet or interior trim.
Any ideas for me?
Thanks!
Yes......have you looked at and tested your dizzy from the other thread yet?
Report back.
Posted by: Tdskip Oct 17 2018, 01:17 PM
Suspects:
- Air leaks. This includes the possibility that the throttle plate isn't closing correctly. Or that the decel valve is hanging open. Or some other air leak.
- Timing. Advanced timing will raise your idle; if the timing sticks advanced it will keep the RPMs up, then when the timing drops so will the RPMs.
--DD
First, thanks to all for the ideas.
Dave - I did find that when I was operating the throttle by hand at one point it seemed to close (but with RPMs still too high) but then it further "snapped" back to closed.
Is there a lip or ridge in there that gets worn or gunked up?
I'll try disconnecting the accelerator pedal and then cable to see if that makes a difference.
Thanks!
Posted by: Tdskip Oct 17 2018, 01:18 PM
1) You must be having some pretty bad leaks if you can not bring the idle down with the screw on the throttle. Replace all vacuum lines and/or test with a carb cleaner spray at all connections.
The air bleed screw does impact the idle level, but it needs to be nearly fully screwed in to lower it.
I'm going to dig into the throttle plate first.
Thanks!
Posted by: TravisNeff Oct 17 2018, 01:47 PM
Put a few drops of oil on your distributor felt, the advance arms may be sticking open. Otherwise it sounds like vacuum leaks.
Posted by: Dave_Darling Oct 17 2018, 04:00 PM
Is there a lip or ridge in [the throttle body] that gets worn or gunked up?
There wasn't one when the throttle body was new. There may be one now... The shaft may also have worn the bore that it rides in out of round. And there could be other potential issues that cause that behavior.
Start isolating things. Disconnecting the throttle pedal will remove that from the equation. If you still have sticking, disconnect the throttle cable at the throttle body end. If you still have sticking, the problem is in the throttle body assembly.
--DD
Posted by: porschetub Oct 17 2018, 06:26 PM
Put a few drops of oil on your distributor felt, the advance arms may be sticking open. Otherwise it sounds like vacuum leaks.
You nailed it,sticking mechanical advance...real common issue,as long as the engine idles @ correct rpm or you have other issues as mentioned.
Posted by: Tdskip Oct 17 2018, 06:53 PM
Good tip on the distributor-I'll have to check that.
I'm used to checking for vacuum leaks using starting fluid and listening to a change in RPM. I did check that today and even after spraying all of the hose junction points. I did not get any change in RPM. Does that suggest that I'm OK as far as vacuum leaks go or do I need to test in a different manner?
Posted by: 76-914 Oct 17 2018, 08:13 PM
Good tip on the distributor-I'll have to check that.
I'm used to checking for vacuum leaks using starting fluid and listening to a change in RPM. I did check that today and even after spraying all of the hose junction points. I did not get any change in RPM. Does that suggest that I'm OK as far as vacuum leaks go or do I need to test in a different manner?
That suggests there are no leaks at the hose connections. But there are other places. Did you spray by the injector seals; the intake manifold body and seals on the runners; the oil fill tower; the throttle body shaft bushings, etc. If those bushings are worn enough it would account for both sticking and vacuum leak Disconnect the cable as I mentioned earlier so you can rule out the cable binding.
Posted by: Tdskip Oct 18 2018, 12:13 PM
Good morning. Just a quick update that I did the test routine that Dave another suggested and it looks like my initial culprit is a sticky throttle cable, RPMs drop quickly and correctly with that disconnected.
Posted by: 76-914 Oct 18 2018, 01:30 PM
Then the tube for the throttle cable is severed or loose; split at the end where the cable has worn thru; filthy; or routed incorrectly.
Posted by: adolimpio Oct 18 2018, 03:37 PM
I had a similar problem recently.
The ends of the wires that make up the cable jacket were very sharp and catching on the cable. I bent the ends of each wire at each end to flare them out a bit and that did the trick - see picture below.
Posted by: worn Oct 18 2018, 05:15 PM
I had a similar problem recently.
The ends of the wires that make up the cable jacket were very sharp and catching on the cable. I bent the ends of each wire at each end to flare them out a bit and that did the trick - see picture below.
That is interesting. Harbor Freight sells a cable Oiler that allows you to push oil into this sort of cable. Not sure what people think about that, but I found it helpful. Cable still seems to stick just a wee bit, but for me it is when I try to accelerate. Mine goes back down just fine.
Posted by: Tdskip Oct 19 2018, 05:37 AM
Thanks for the great info and discussion.
Any recommendations on a specific replacement cable?
Posted by: DRPHIL914 Oct 19 2018, 08:09 AM
Thanks for the great info and discussion.
Any recommendations on a specific replacement cable?
You can get a really good cable replacement from any supplyer that advertises here,
GPR, 914rubber, Auto Atlanta, Sierra Madre, etc use one of our site sponsors and those that sponsor the outings like the Okteenerfest, WCR etc
Phil
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