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Throttle body and cable problem

8

86redMed

Guest
Hi everybody,

my Vette seems to have a problem with the throttle cable: when the engine is off, the throttle pedal is smooth. But once the engine has cranked, when I try to push the pedal, it is first really hard to push and then smooth like when the engine is off. So, I cannot control the acceleration...

I've checked the cruise control cable and I really think it is not involved in that problem. I've lubricated the throttle cable and adjusted the T.V. cable with no effect.

To my mind , the problem comes from the throttle body: when the throttle valve is closed, you have to make a real effort to open it, but once the air can flow , it is less difficult. Perhaps my throttle body needs to be repaired? Or perhaps is it a normal condition ?

I need an advice...
 
C

c4ever

Guest
Have you cleaned the throttle body assembly? They recommend cold immersion type cleaner. DO NOT IMMERSE ENTIRE UNIT. TPS,IAC,seals and gaskets can not be immersed. Remove these items if you intend to soak unit.
Best of luck. Hope it helps some.;)
 
B

Bill C

Guest
86

I had the same problem! I completely disassembled the throttle body (TB) and cleaned it. The EGR gas ports are directly behind the throttle blades and make a real mess on the back of them. If you have not ever cleaned them, your best bet is to remove the throttle body. While it is off you can clean the IAC (idle air control) valve pintle,, seat and ports and the inside of the upper plentum. They will be really guncked up. I used brake parts cleaner and carb cleaner. Dont soak any electrical part. Just wipe them off. I also replaced any vacuum lines and hoses that were accessable. The little plastic vacuum lines are very easy to break. If you remofe hoses off of them I would slice them off rather than twisting them off. :)

**BE VERY CAREFUL WITH THE COOLANT PASSAGE SEREWS** I soaked mine in "B-Blaster over night and they were fine. If they show any signs of being stuck **LEAVE THEM ALONE** A friend of mine rung off all of his and had to drill, tap and helicoil it.

Upon re assembly and prior to bolting up the TB I lubericated the throttle shaft (inside and on the outside) with a spray lithium grease and worked the throttle shaft open and closed until it was nice and free. Wipe off any excess from the inside. You dont know what that stuff will do to yoyr O2 sensor! :0 For the outside I just sprayed it through the spring and it flowed in just fine.

One last thing... I by-passed my TB coolant passage by hooking the coolant hoses together with a piece of hardware store brass pipe and it made a tremendous difference in how cool the upper plenumn stays. Cooler air means more horse power!!!

Once you clean the TB the first time the correct way, every other oil change or so, I block open the throttle blades and spray carb cleaner in and manualy wipe the blades down with a rag wrapped around my finger.

I have not had a problem since. You will also notice that you will also have a smother idle and less idle surge!!!!!!!!!!!!!!!! That has to be worth all this effort! :) ;)

GOOD LUCK!

BILL C
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
The removal and cleaning is an excellent idea. However, before you spend too much time cleaning it, hold it in your hand and watch the movement between the throttle shaft and the blades. It is also possible that you have excessive wear in the bushings allowing the throttle blades to wiggle side to side in the bore. When you first fire and run the car, the added vacuum of the engine behind the blades may cause them to bind up on the wall. You will be able to tell if something is wrong when you remove it because there will be fresh clean scraping look at a corner or top area next to the blades.

If this is the case, you might be able to dissasemble, drill and machine new bushings, or just replace the unit.

This is worst case. Otherwise my money would be on it just plain full of carbon and crud.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
All good advise

I'm betting a worn out throttle body...

Grab it from the cable pull side and wiggle it, if you can life is bad.

The good news, I had mine rebushed for 100.ish

Remove the MAF sensor and look down the throats.. if you see scuff marks.. AND have the wiggle, problem solved... well almost!

I would be VERY careful using carb cleaner around the intake.. that stuff is DEATH to the CAT's.

Spray a little on a rag & wipe..let it evaporate
BEFORE starting..

I sprayed just a tiny bit on my 84 Bronco to free up the the choke.. 2 weeks later.. new CAT needed! It plugged up from just that.


Mike
 
8

86redMed

Guest
Thanx for your advices...

...Unfortunately it is what vigman suspected: the throttle shaft has an excessive play !!

I'll try to do a complete cleaning perhaps in a few days.

But, where can I find a new TB ?
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Merde!

Looks like mail order por vous!

I have NO idea in France where you would get Vette parts....


Look in the C-2 section and contact some of our British pal's they might know where the Vette Euro connection is.

I would try the Web sites for Mid America, Ecklers, Summit etc and check out their prices.

I have an 86 TB assy ready to go ( old but usable ) but I have no idea how much shipping ( etc ) would be.


Mike
 
8

86redMed

Guest
Of course vigman !

All of my parts are bought in America (Zip,Ecklers, etc...).

But what is the size for a stock throttle body ? 42 mm or 52 mm ?
 

FrankM

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
86redMed said:
Thanx for your advices...

...Unfortunately it is what vigman suspected: the throttle shaft has an excessive play !!

I'll try to do a complete cleaning perhaps in a few days.

But, where can I find a new TB ?

While the throttle shaft may have excessive play, it takes alot to make a difference.

You can take the throttle body to a carburator shop and they can rebush it. I paid $20 for teflon rebushing. No drilling needed.

Also, before I actually would go the rebush route I would, after cleaning plate and bore, reset the minium idle. Over time the set screw wears and the plates stick in the bore. Its noticibly only when running. If the minium idle is correct the plates are unable to stick in the bore due to the needed gap for minium idle.

try it!!!:_rock
 
B

Bill C

Guest
Frank has an excellent suggestion!!! Few people know about the minimum idle setting and even less know how to properly accomplish it. Its in the repair manuals. Too bad, it's an easy thing to do and can fix alot of the driveability problems that are associated with most high mileage TPI systems. Don' t forget to adjust the Throttle Position Sensor (TPS) after the min idle is set. My car has 175K on the meter and I have a little bit of shaft wobel too. I cleaned it, set the min idel and it worked out GREAT!
Bill C
 
8

86redMed

Guest
Well, mine has "only" 76.500 miles...

But, I will study all your advise . Thank U very much !!!
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
Would a sticking TB plate cause a slow-to-fall idle? When cold, and I stop at a traffic light, my idle will be around 1600 RPMs but over the next 30 seconds or so it'll drop back down to 900. Doesn't happen as much after the engine is warm, but it does occasionally. No, there's no free play in the shaft.
[RICHR]
 

FrankM

Well-known member
Joined
Nov 4, 2001
Messages
154
Location
Derry, NH
Depends on:
if you are driving the car every day and this happens it could be a sticking IAC. Its on the side of the throttle body.

if you just replaced the battery or took it out of storage the ECM could be learning its idle strategy and will get better in a
day or two.

if you have a vacuum leak this scenario could happen too
 
B

Bill C

Guest
Sounds like you have a vacuum leak. To help locate them I use a one gallon jug connected to a small hose that can flow a small stream of water and let the water flow over all of the gasket areas. If there is a leak when the engine is at idle it will SUCK the water in and the idle will change a bit while the water is sealing up the leak. Check all of your vacuum lines too. If they are all good you may need a good throttle body cleaning.
Bill C
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
Thanks, guys. I'll check for a vacuum leak this weekend. I've also got a vacuum gauge, but I'm not sure what the readings should be in various locations.
[RICHR]
 

69MyWay

Well-known member
Joined
Jul 3, 2001
Messages
4,364
Location
Auburndale, Florida
Corvette
1969 Killer Shark
Here is another great vacuum leak check.

If you smoke, or have a friend that smokes, have them puff away on a cig, then blow into a vacuum port on the intake (The PVC hose is a good one because it is large and goes into the base of the intake). Now, watch the intake. You will see a whisp of smoke come out where there is a leak!
 

Ken

Gone but not forgotten
Joined
Jan 30, 2001
Messages
8,236
Location
Hermosa Beach, CA
Corvette
1987 Z51 Silver Coupe
Propane works too; the rpm's will increase if there's a leak. ;)

_ken :w
 

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