1985 Idle increase
Thread Starter
Instructor
Joined: Feb 2014
Posts: 145
Likes: 5
From: Dunkirk Md
1985 Idle increase
While running my 1985 C4, I increase RPM all is fine I let off the gas and the idle stays around 1100 to 1500. If I tap the gas pedal it will idle down to 600. Take off again same thing. I have the Factory Manual and nothing there! any ideas?
This started after I replaced
8 new bosch 3 Injectors
all sensors on eng
New throttle Body
A lot of new connectors that were cracked
New fuel pressure regulator dia
Plugs
Cap Rotor
This started after I replaced
8 new bosch 3 Injectors
all sensors on eng
New throttle Body
A lot of new connectors that were cracked
New fuel pressure regulator dia
Plugs
Cap Rotor
Safety Car
Joined: Aug 2009
Posts: 3,751
Likes: 276
From: Melbourne, Victoria, Australia
Hi
yes as John has mentioned check the throttle body, remove the cables
from the throttle body and fit one at a time.
See which one is too tight and won't let the throttle body to return fully.
Note. Do not adjust the idle screw, It needs to be set following the base idle procedure in your shop manual.
I would also check the cruise control cable how much page there is,
if it is adjusted to tight it will cause what you are describing.
You can adjust it at the Cruise control, loosen the nut and turn clockwise half to one turn to take the tension of.
Then your Throttle body should return freely and fully
yes as John has mentioned check the throttle body, remove the cables
from the throttle body and fit one at a time.
See which one is too tight and won't let the throttle body to return fully.
Note. Do not adjust the idle screw, It needs to be set following the base idle procedure in your shop manual.
I would also check the cruise control cable how much page there is,
if it is adjusted to tight it will cause what you are describing.
You can adjust it at the Cruise control, loosen the nut and turn clockwise half to one turn to take the tension of.
Then your Throttle body should return freely and fully
Drifting
Joined: Jun 2013
Posts: 1,590
Likes: 60
From: ft myers FL/Munising MI
when I got my 85, the tb and plenum were full of carbon....hard to believe the butterfly could ever close right.....i'd be spraying some tb cleaner up in there.....at least put a eyeball on the inside of the tb..
Team Owner
Joined: Jul 2004
Posts: 28,467
Likes: 3,288
From: Hartford WI
Get the car to an autozone and borrow their scanner. By then the engine should be at operating temp. First thing you want to do is to reset the IAC.
Get the IAC counts from the scanner and see. If it is over 20, it means the IAC is opening up to allow more air in. Screw in the adjustment screw. If it is under, it means the reverse and do the reverse. Once that is set, check the TPS to be at 0.54V.
NOTE: This is all done after you are sure that the timing is correct and there are no leaks in the air lines.
Get the IAC counts from the scanner and see. If it is over 20, it means the IAC is opening up to allow more air in. Screw in the adjustment screw. If it is under, it means the reverse and do the reverse. Once that is set, check the TPS to be at 0.54V.
NOTE: This is all done after you are sure that the timing is correct and there are no leaks in the air lines.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 145
Likes: 5
From: Dunkirk Md
1985 C4 auto all stock- no vac leaks!
Got back to trouble shooting this issue. Here is what I did with no results there is new behavior. With the engine running I shut ignition off and engine shut down, the throttle body in all cases below released!
In all cases above as soon as I shut the ignition off and engine shuts down the throttle body would close . I checked with engine off no binding >
I am at a loss! If the throttle body was binding it would bind with the engine on or off
Got back to trouble shooting this issue. Here is what I did with no results there is new behavior. With the engine running I shut ignition off and engine shut down, the throttle body in all cases below released!
- Disconnected all cables, gas pedal, auto trans cable, and Cruise control cable. Ran engine problem still there.
- Disconnected and plugged vac line to pass side valve cover, no change
- Disconnected water line and plugged , no change
- Disconnected TPS, reinstalled checked voltage per chop manual, no change.
- Disconnected IAC. No change
- Disconnected Mass Air sensor and Intake Air duct, no change
In all cases above as soon as I shut the ignition off and engine shuts down the throttle body would close . I checked with engine off no binding >
I am at a loss! If the throttle body was binding it would bind with the engine on or off
Last edited by agillings; Dec 14, 2014 at 02:56 PM.
Instructor
Joined: Nov 2011
Posts: 147
Likes: 0
From: Florida
Are you saying that after you shut the engine down the Throttle plate in the throttle body would close????
If the TP in the TB is open with nothing touching it, it is defective. Ask for a refund. It should return to a shut position easily. It should do that with or without the engine running.
If the TP in the TB is open with nothing touching it, it is defective. Ask for a refund. It should return to a shut position easily. It should do that with or without the engine running.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 145
Likes: 5
From: Dunkirk Md
Are you saying that after you shut the engine down the Throttle plate in the throttle body would close????
If the TP in the TB is open with nothing touching it, it is defective. Ask for a refund. It should return to a shut position easily. It should do that with or without the engine running.
If the TP in the TB is open with nothing touching it, it is defective. Ask for a refund. It should return to a shut position easily. It should do that with or without the engine running.
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Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
1985 C4 auto all stock- no vac leaks!
Got back to trouble shooting this issue. Here is what I did with no results there is new behavior. With the engine running I shut ignition off and engine shut down, the throttle body in all cases below released!
In all cases above as soon as I shut the ignition off and engine shuts down the throttle body would close . I checked with engine off no binding >
I am at a loss! If the throttle body was binding it would bind with the engine on or off
Got back to trouble shooting this issue. Here is what I did with no results there is new behavior. With the engine running I shut ignition off and engine shut down, the throttle body in all cases below released!
- Disconnected all cables, gas pedal, auto trans cable, and Cruise control cable. Ran engine problem still there.
- Disconnected and plugged vac line to pass side valve cover, no change
- Disconnected water line and plugged , no change
- Disconnected TPS, reinstalled checked voltage per chop manual, no change.
- Disconnected IAC. No change
- Disconnected Mass Air sensor and Intake Air duct, no change
In all cases above as soon as I shut the ignition off and engine shuts down the throttle body would close . I checked with engine off no binding >
I am at a loss! If the throttle body was binding it would bind with the engine on or off
Thread Starter
Instructor
Joined: Feb 2014
Posts: 145
Likes: 5
From: Dunkirk Md
The throttle shaft or housing is worn and it is binding in the throttle body from the force that is on the throttle blades, which is created by the engine vacuum at idle. You turn the car off the vacuum goes away and the throttle body closes. I had this same problem and I sprayed some WD 40 on the throttle body to throttle shaft bores and the throttle would work fine for a few months and then I would have to do it again. You can take the throttle body apart and clean out any dirt that is in there to fix the problem. If the throttle body is worn you may have to bush the throttle body or replace it to fix the problem. (FYI at 15" of vacuum the force on the throttle body shaft is 40 lbs)
So I ordered a replacement we will see what goes on after I receive the new one
Thanks Art
Last edited by agillings; Dec 15, 2014 at 02:27 PM.