Some of you were already helping me with a sticking throttle problem a few days ago.
I got a lot of good feedback and checked most of it.
I thought I had the problem solved after finding a vacuum hose off under the throttle body After taking the car out of the driveway and out for a good drive this morning I realised that the throttle still sticks. Possibly not as badly but it does still stick.
This is the previous thread.
http://forums.corvetteforum.com/showthread.php?t=889367

CFI-EFI, you mentioned the throttle shaft.
Could you tell me a bit more about this throttle shaft and how I check to see if this is the problem?

If anyone else has any ideas of what it could be please help.
Thank you.

Jeff

 

This is probably too obvious, but did you check the throttle cable itself to make sure it is properly seated and no strands of cable have broken and rubbing on the thingie it attaches to?

 

I just read the thread and in light of everything thats been suggested and checked I was wondering this myself. Where the cable rides that little half moon groove, if there is any cable fray or wear it could catch up there. Also , that long oval cruise control cable connection at throttle body could hang up and cause a stick if there's a burr or any obstruction. One more thing, are we sure the return spring is good and is not binding or played out?? Sometimes we dive into the difficult checks and overlook the simple. Just my .2 cents

 

The throttle shaft rotates in the bores drilled in the TB housing. As the car gets older and accumulates miles, the shaft and the TB casting can wear. This can be the cause of a vacuum leak and/or the shaft binding in the egg shaped bores. Mind you, I'm not speaking of the throttle bores, but the bores in the TB that the butterfly shaft passes through. It is possible that the binding will only occure with the engine running, the air flow "loading" the shaft in the bore. This is a common carb problem too. You may have a local carb/TB shop that can check the shaft, and bore, bush, and ream the shaft holes to cure the problem.

Checking it could be harder than curing it. You would have to remove all the external pressures on the shaft and check for excessive play. PART of the external pressure comes from the return spring. I would be inclined to use some dedutive reasoning. Remove all cables and linkages from the TB. First make sure the throttle arm moves freely, and that the TPS isn't hanging it up. Then run the engine and see if it sticks. If there are no outside forces and it sticks, I think you've narrowed down the problem.

RACE ON!!!

 

I have the same problem, it's periodic though. It seems like it's gotta be IAC or something computer controlled letting air in, but it can hang open up to 2000 rpms or so.

Does yours stick ALL the time?

 

I tracked my similar problem down to a throttle cable binding near the gas pedal.

 

Thanks guys,
The throttle cable is not frayed anywhere it is visible, I can't speak for inside the sheath or tube it runs through. It does seem to slide freely in and out.
92corvette, how did you diagnose the cable to be sticking near the gas pedal?
The spring seems good because it works very well when the car is off.
Really quite a good resistance when I press against it to open the throttle but much more so when the car is off than when running.

CFI-EFI, I am going to check to see if there is much play in the butterflies. If there is I would assume it's the throttle shaft.
I don't live in a city so finding a good carb/TB shop is going to be tough.
If I do diagnose this to be the problem it may be cheaper to find a good used throttle body on ebay or somewhere.
It wasn't that I was ignoring your advice before, I just really wanted it to be something else.
With the number of people who are going to larger ones it should be easy to find a good stock one.

Skateparkdave you asked about the spring, is it possible that the spring became unwound slightly when the throttle body was off the car and it was off the throttle body? Maybe it simply needs to go around one more time? I didn't take it off so I don't know if this is possible or not.

Centralcoaster, it seems to stick all the time when I let go of the throttle fairly gently like if I'm just cruising. If I am on and off the gas fairly heavy it does not seem to stick.
It does seem to be the same with the rpms It has stuck as high as around 1900 for me.

I think I may need to take this one to a shop.
I like to tinker and I love the feeling of accomplishment when I fix something myself, plus the money I save.
The thing I hate is that so often I go to a shop and I get the feeling that they are guessing, just replacing parts, or that I could have done it myself.
I would bet many of you feel the same way.

 

Sometimes sticking is caused by a buildup of carbon on the backside of the butterflies, but, if I remember correctly, you had someone clean the TB, right?

Did he clean the backside of the butterflies?

If you remove the accordian which connects between the MAF and the TB and open the butterflies by hand, you can look inside and see if there's a carbon build-up.

Speaking of accordian, make sure the clamp tightening gizmo isn't position in such a way as to interfere with the TB lever. I believe that if the clamp is placed incorrectly it'll only effects WOT, but you might as well check anyway.

Have you tried spraying WD-40 on the shaft?

Sorry, I sold my stock 48 mm TB to someone who was having a similiar problem. He thought he had a worn shaft too.

One more thought: Was the throttle body doing this BEFORE you had it worked on or is this something that began AFTER?
Jake

 

Thanks Jake,
I sprayed WD40 on everything on the outside.
I will do the parts where the Butterfly rotates or rests.
As far as cleaning the back of the butterfly I can only assume that it was cleaned too so I will check it.
It definately started after the work was done. I'm scratching my head trying to think if it was the same time or two days later but it was somewhere between the two.
The accordian is out of the way.
Thanks again

 

I agree with CFI-EFI - he says it all.

My throttle is as he described, only binds with engine running, because the load of air rushing through bends the spindle or jams it in the worn out housing. It will get so sticky I have to bang the throttle pedal to accelerate (not a good idea, it's plastic)

I take the air boot off every 2 - 3 months and spray lithium grease, using the thin tube supplied with the can, into the spindle bore from inside and out, 2 or 3 times - that's both sides of the ends and the centre column. Sometimes this blocks the IAC hole so I give that a clean with carby cleaner spray.

For a while the throttle will be 'smooth as', then will start to get stiffer until I re apply the grease.

Hope this helps.

Solution is either a new TB or have bushes or bearings fitted to existing TB as I plan to do. I want to see if I can buy a new spindle, haven't located that yet.

S'nut

 

Thanks S'nut.
Sounds exactly like my problem.
I figured CFI-EFI knew what he was talking about but like I said earlier I was willing to try everything else first because I didn't wan't this to be the problem. I knew it was a little toughter to fix when I didn't really understand what he said.
Lithium grease...should have some of that around here somewhere.
I'll let you all know how I make out.
Thanks

 

I guess anything is possible but since I've never had mine off I'd be lieing if I said either way. What I do know is that springs typically have a life span and after however many cycles get "sprung", or at least lose strength. Now the ones on our C4's must be outstanding because it's not a common trouble. I'm just wondering if, like you said, because it has been grease monkey'd with (mechanic) that maybe it did get stretched or unwound or sprung a bit. I'm not sure how you could check short of replacing..Who knows ? I'm like you in that I'm just shooting fish in a barrel on this one..just thought it may be something to check. Best of luck.

 

Now that you understand it, can you help me? How might I have explained it more clearly?

RACE ON!!!

 

Here's another thought, I cleaned my throttle body, was very dirty and the blades were sticking closed. Afterward, it picked up a whistling around the shaft. Believe I cleaned out the gunk from around the shaft at the bushings and created an airleak where before the crud had the throttle shaft bores sealed. maybe you have kinda the same thing, cleaned out and now shaft bores are misshapen. I just got a new throttle body from Superior Chev. Price was within a few dollars of a rebuilt one,

 

These are the WORST types of problems to bring to a shop. They'll do the same as you, except start from scratch dicking around with everything and charging you a helluva lot for it. The only times outsourcing your repairs should be considered is when the problem has been identified, and when the repairs require specialized training or equipment.

Do you really think the service tech will be any better at tinkering with your car than you will?

 

If the throttle body was off for cleaning and wasn't torqued down at 18 ft lbs...even if just one bolt is tighter or more loose, the TB will be twisted and effect the shaft...triple check the torque on the 4 bolts and WD40 the shaft behind the spring. also, a temporary test would be to add a reasonably stiff spring and she if the idle returns when it should.

One other thought...next time she is idling high, leave it running and open the hood. Look for a space or gap that might indicate that the shaft isn't returning to the stop.

 

I was at wits end with my '86 and it's idle problem:

http://forums.corvetteforum.com/showthread.php?t=868977

After having my TB rebuilt with roller bearings on the shaft and checking EVERYTHING on the outside of the motor, I decided to live with it... Then I went on to change my intake manifold gasket, a BIG job, because it was leaking coolant at the right rear near the distributor (first thought was to use that Bart's stuff to cure the leak but decide to do it the right/hard way). The lower base manifold gasket appeared 'wet', i.e. as though it was leaking from the inside of the lifter valley. In addition, spark plugs were extraordinarily clean as though engine was running lean with some having black splashy deposits on the insulator, which woiuld be consistent with ingesting oil from the lifter valley. While I was at it I also had my injectors cleaned and tested at Cruzin Performance (weren't in bad shape to begin with based on the before/after test results) and also replaced my EGR although I did not suspect the original was bad (just did it while I had everything apart). Anyway, after cleaning and assembling everything and readjusting the TPS & min idle air, the HIGH IDLING PROBLEM WENT AWAY COMPLETELY Been driving around for a few days now with no recurrence of the problem -- even open the hood sometimes to check the threshold of throttle shaft binding with a hot running engine and it doesn't have any tendancy to bind as it had in the past. Did not lube the throttle body or even clean it since it was still shiny from the rebuild. I believe that I had a significant intake manifold leak that was causing the problem although it wasn't evident on a vacuum gauge.

 

I've posted this before, but here's what I'd do:

I'd remove ALL three cables from the TB, the cruise, the trans and the throttle cables. This will eliminate them as a possible cause.

I'd then start the engine and let it warm up to the point that you'd experienced the sticking before.

I'd then operate the throttle BY HAND, slowly, watching for and sign of sticking or binding.

If there is NONE, then I'd tend to think it's one or more of the cables that is keeping the butterflies from closing properly.

The cruise control would be my first thought. If it's set too tightly it can cause the butterflies not to close properly. It's easily adjusted right at the servo (above the battery)

If the sticking/binding STILL OCCURS, then I'd gradually loosen the four bolts that attach the TB to the plenum. Loosen each one a little, then check for binding. If it still binds, loosen each one a tad more.

If the binding goes away, then you'd tweaked the TB.

If NOT and the butterflies STILL BIND, I'd next look to the minimum air flow setting.

I just posted on this on another thread, so not wanting to write it all over again, the short version is: If the butterflies are set TOO tight, that is TOO MUCH in the closed position, the blades, themselves, will be in contact with the TB bore and this WILL cause sticking/binding.

Use the minimum airflow setting precedure (IAC disconnected) and set Min Air Flow to give an idle RPM of 550 rpms. The ECM will compensate for this change. Then re-adjust the TPS voltage because it changes when you move the torx screw.. This may cure it.

Keep us posted.

Jake

 

Thanks Guys,
I couldn't get to a computer yesterday.
CFI-EFI, you likely explained it fine, I just didn't know what the parts were that you were referring to.
I just learned what a throttle body was this summer.
Going inside it was beyond me. As I said I had someone else take it off and clean it for me. Looking at it now I would likely attempt it.

I didn't have any lithium grease but I had some teflon lubricant.
I tried to wiggle the butterflies to see if there was any movement. I figured this would tell me if the fitting had become worn.
They didn't move at al. I then sprayed the lubricant around where the butterfly touches the TB and took the car for a drive.
Nothing changed.
I would even say that it was worse. It didn't seem to stick as long but it would stick at higher rpms.
I have tried taking off two of the three cables because I wasn't sure how to disconnect the throttle one. The other two made no difference so the cruise control cable is off the list. I need to go bakc and figure out how to disconnect the throttle cable to see if it is the culprit.
Process of elimination seems to be the only way to do this.
The throttle body bolts were quite loose when I checked them.
I tightened them back up to 18 lbs.
I could try loostening and tightening them one at a time.
I suppose it could also be possible that the butterfly got bent or out of shape a little if to much force was used to clean it. This could cause it to rub a little in the bore.
Not sure how to check this but maybe with a mirror.
1986Z51 that looks like a lot of good information.
I started reading the thread you linked me to but will need to get back to it.
I would say I have the exact same symptoms as you did.
1300 rpm is what it usually idles at until I blip it. On the highway I have had it stick over 2000 rpms now and it seems to be climbing.
I'll be back.
Thanks

 

I just tried disconnecting all three cables that hook up to the side of the throttle body.
With all three cables disconnected the throttle would still stick while running.
Again I tried to wiggle the butterfly but there is no play in it. If the points where the butterfly rests or the butterfly itself were worn wouldn't there be some play?
I disconnected the tps as well to see if it had any effect but there was no difference.
I'm not sure if this indicates anything, I was hoping someone could tell me.
Next I'm going to play with the 4 bolts that hold the throttle body to the plennum. I'll see if loostening and tightening these in all different combinations makes any difference at all.
I'm still looking for lithium grease to see if a good lube will stop the sticking. (I've looked everywhere but the store so far)
I have been avoiding the electrical testing because this gets a little trickier for me. If the bolts and the grease do nothing for me I'll start checking voltages of the tps and whatever else you people suggest I check.
Thanks