| Author |
Message |
random electron
Guest
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 Posted:
Sun Jan 02, 2005 6:11 pm Post subject:
Help: 1988 5.7 TBI GM Engine - high idle |
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Hi,
The idle on this engine is high. My shop mechanic says it is the gasket
between the tbi and air intake. I replaced it and see no difference. Any
other ideas?
tia
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Bret Chase
Guest
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| Posted:
Sun Jan 02, 2005 7:09 pm Post subject:
Re: Help: 1988 5.7 TBI GM Engine - high idle |
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On Sun, 02 Jan 2005 13:11:26 GMT, random electron <fake@fake.net>
wrote:
| Quote: | :|Hi,
:|
:|The idle on this engine is high. My shop mechanic says it is the gasket
:|between the tbi and air intake. I replaced it and see no difference. Any
:|other ideas?
:|
:|tia
|
start spraying around all gaskets and vacuum lines w/ some carb
cleaner... when the idle drops, the spot you just sprayed is where the
vacuum leak (and the high idle) are coming from.
-Bret |
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Jonathan Race
Guest
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| Posted:
Sun Jan 02, 2005 10:31 pm Post subject:
Re: 1988 5.7 TBI GM Engine - high idle |
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The TBI gasket was a good place to start, but not the only thing that could
give you a high idle. The next thing is the IAC (Idle Air Control) valve.
The IAC allow air to bypass around the main air flow path when at a zero
throttle condition - it's position is controlled by the ECM depending on a
number of factors, which in turns adjusts your idle up or down. On a motor
that old, it probably has some crud on the pintle or valve seat not allowing
it to seal completely, giving you a high idle. Either that or it's worn and
won't seat, another age related condition. A new IAC valve will run about
$60.00 and take around 20 minutes to install. Remember to clean the seat in
the TBI before installing the new IAC valve.
After the IAC valve, check your coolant temperature sensor. A faulty sensor
giving an abnormally low reading will make the ECM think the motor isn't
warmed up yet causing it to idle high.
Good luck - Jonathan
--
Jonathan A. Race
Lieutenant, EMS Supervisor
Orange County (FL) Fire Rescue Department
(This message may contain personal opinions and/or information not related
to my employment or employer)
"random electron" <fake@fake.net> wrote in message
news:Xns95D252EB111F0fakefakenet@69.28.186.158...
| Quote: | Hi,
The idle on this engine is high. My shop mechanic says it is the gasket
between the tbi and air intake. I replaced it and see no difference. Any
other ideas?
tia |
|
|
| Back to top |
|
|
Ted Mittelstaedt
Guest
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| Posted:
Mon Jan 03, 2005 3:35 am Post subject:
Re: 1988 5.7 TBI GM Engine - high idle |
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|
"random electron" <fake@fake.net> wrote in message
news:Xns95D252EB111F0fakefakenet@69.28.186.158...
| Quote: | Hi,
The idle on this engine is high. My shop mechanic says it is the gasket
between the tbi and air intake. I replaced it and see no difference. Any
other ideas?
|
Why would it be that gasket? Engine vacuum is present after the throttle
plates not before.
Why is it a vacuum leak at all? Do your plugs show a lean
condition? Have you run through an emissions test station and they say it's
lean?
Ted |
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random electron
Guest
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| Posted:
Mon Jan 03, 2005 4:15 am Post subject:
Re: 1988 5.7 TBI GM Engine - high idle |
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"Jonathan Race" <jonrace@earthlink.com> wrote in
news:ydWBd.15385$RH4.9693@newsread1.news.pas.earthlink.net:
| Quote: | The TBI gasket was a good place to start, but not the only thing that
could give you a high idle. The next thing is the IAC (Idle Air
Control) valve. The IAC allow air to bypass around the main air flow
path when at a zero throttle condition - it's position is controlled
by the ECM depending on a number of factors, which in turns adjusts
your idle up or down. On a motor that old, it probably has some crud
on the pintle or valve seat not allowing it to seal completely, giving
you a high idle. Either that or it's worn and won't seat, another age
related condition. A new IAC valve will run about $60.00 and take
around 20 minutes to install. Remember to clean the seat in the TBI
before installing the new IAC valve.
After the IAC valve, check your coolant temperature sensor. A faulty
sensor giving an abnormally low reading will make the ECM think the
motor isn't warmed up yet causing it to idle high.
Good luck - Jonathan
|
Thanks for the advice, I will check this out. |
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Jonathan Race
Guest
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| Posted:
Mon Jan 03, 2005 5:13 am Post subject:
Re: 1988 5.7 TBI GM Engine - high idle |
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|
A leak in the gasket between the TBI and the intake manifold allows
additional air into the intake system outside of the control of the
butterfly valves or the Idle Air Control valve. More air = higher idle. In
1988, the gaskets were fiber based and known to split after 10-15 years or
more, causing the air leak. Although it was a good idea to install a new
gasket - it probably was due even if it wasn't split and leaking already -
but I would have checked the IAC valve first, tested the coolant temperature
sensor next, then moved on to the new gasket. The vehicle in question is a
1988, so I'm betting it's the IAC valve. I put close to 200,000 miles on my
old '88 Chevy C1500 pick up with the 350 TBI, and all three needed replacing
over time before I sold it.
Cheers - Jonathan
--
Jonathan A. Race
Lieutenant, EMS Supervisor
Orange County (FL) Fire Rescue Department
(This message may contain personal opinions and/or information not related
to my employment or employer)
"Ted Mittelstaedt" <tedm@toybox.placo.com> wrote in message
news:newscache$33op9i$8e21$1@news.ipinc.net...
| Quote: |
"random electron" <fake@fake.net> wrote in message
news:Xns95D252EB111F0fakefakenet@69.28.186.158...
Hi,
The idle on this engine is high. My shop mechanic says it is the gasket
between the tbi and air intake. I replaced it and see no difference. Any
other ideas?
Why would it be that gasket? Engine vacuum is present after the throttle
plates not before.
Why is it a vacuum leak at all? Do your plugs show a lean
condition? Have you run through an emissions test station and they say
it's
lean?
Ted
|
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Hayman
Guest
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| Posted:
Mon Jan 03, 2005 7:52 am Post subject:
Very common on GM TBI's |
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|
The throttle body base gasket is a common problem on those trucks. Trick is
(engine off) to climb on top open throttle plates and look down into
throttle body with light. Normally you can see the gasket sucked into the
intake area.
I agree the TB base gasket would be the first place to check on those
trucks. If that looks good then proceed on from there. Now does the
engine idle high all the time??? Did you check of all the vacuum lines
make sure there not cracked or broken. Take a pliers and pinch them off
one at a time right where they connect to the intake to make sure there is
no leaks etc.
The IAC on the side of the TBI can also act up. If old the shaft can gum
up over time etc. Remove it and clean it with carb cleaner and a tooth
brush etc. When you take it out note in what position it is in i.e out or
in.
Have you checked codes?? If you jump A&B on the ALDL and turn on the
ignition the engine service light will flash codes. Also on old GM TBI's
when you jump A&B it cylcles the IAC.
Stop by a parts store and pick a service manual for 15 bucks it has lots
procedures for those old truck.
As for throttle body fuel injection that old GM set up was a pretty good
one. WE didn't make a lot of money off of them. The base gasket problem
and bad distributor cabs is all I can think of that was a common failure. |
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random electron
Guest
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| Posted:
Tue Jan 04, 2005 7:52 am Post subject:
Re: 1988 5.7 TBI GM Engine - high idle |
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Thanks, Jonathan, I'll try it this weekend.
"Jonathan Race" <jonrace@earthlink.com> wrote in
news:870Cd.5382$Cc.3179@newsread3.news.pas.earthlink.net:
| Quote: | A leak in the gasket between the TBI and the intake manifold allows
additional air into the intake system outside of the control of the
butterfly valves or the Idle Air Control valve. More air = higher
idle. In 1988, the gaskets were fiber based and known to split after
10-15 years or more, causing the air leak. Although it was a good
idea to install a new gasket - it probably was due even if it wasn't
split and leaking already - but I would have checked the IAC valve
first, tested the coolant temperature sensor next, then moved on to
the new gasket. The vehicle in question is a 1988, so I'm betting
it's the IAC valve. I put close to 200,000 miles on my old '88 Chevy
C1500 pick up with the 350 TBI, and all three needed replacing over
time before I sold it.
Cheers - |
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random electron
Guest
|
| Posted:
Tue Jan 04, 2005 7:52 am Post subject:
Re: Very common on GM TBI's |
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|
Thanks Hayman,
I'll try it this weekend.
"Hayman" <Hayman@nospam> wrote in
news:daa6fd35314a699056b67e1bd72b3843@localhost.talkaboutautos.com:
| Quote: | The throttle body base gasket is a common problem on those trucks.
Trick is (engine off) to climb on top open throttle plates and look
down into throttle body with light. Normally you can see the gasket
sucked into the intake area.
I agree the TB base gasket would be the first place to check on those
trucks. If that looks good then proceed on from there. Now does the
engine idle high all the time??? Did you check of all the vacuum lines
make sure there not cracked or broken. Take a pliers and pinch them
off one at a time right where they connect to the intake to make sure
there is no leaks etc.
The IAC on the side of the TBI can also act up. If old the shaft can
gum up over time etc. Remove it and clean it with carb cleaner and a
tooth brush etc. When you take it out note in what position it is in
i.e out or in.
Have you checked codes?? If you jump A&B on the ALDL and turn on the
ignition the engine service light will flash codes. Also on old GM
TBI's when you jump A&B it cylcles the IAC.
Stop by a parts store and pick a service manual for 15 bucks it has
lots procedures for those old truck.
As for throttle body fuel injection that old GM set up was a pretty
good one. WE didn't make a lot of money off of them. The base gasket
problem and bad distributor cabs is all I can think of that was a
common failure.
|
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random electron
Guest
|
| Posted:
Thu Jan 13, 2005 7:55 am Post subject:
Re: 1988 5.7 TBI GM Engine - high idle |
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|
random electron <fake@fake.net> wrote in news:Xns95D3E834C3FDBfakefakenet@
69.28.186.158:
| Quote: | Thanks, Jonathan, I'll try it this weekend.
"Jonathan Race" <jonrace@earthlink.com> wrote in
news:870Cd.5382$Cc.3179@newsread3.news.pas.earthlink.net:
A leak in the gasket between the TBI and the intake manifold allows
additional air into the intake system outside of the control of the
butterfly valves or the Idle Air Control valve. More air = higher
idle. In 1988, the gaskets were fiber based and known to split after
10-15 years or more, causing the air leak. Although it was a good
idea to install a new gasket - it probably was due even if it wasn't
split and leaking already - but I would have checked the IAC valve
first, tested the coolant temperature sensor next, then moved on to
the new gasket. The vehicle in question is a 1988, so I'm betting
it's the IAC valve. I put close to 200,000 miles on my old '88 Chevy
C1500 pick up with the 350 TBI, and all three needed replacing over
time before I sold it.
Cheers -
|
Thanks everyone. The TBI gasket fixed the problem. Easy and cheap fix.
Regards |
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parkerea
Joined: 16 Jan 2005
Posts: 3
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| Posted:
Sun Jan 16, 2005 7:05 pm Post subject:
re:Help: 1988 5.7 TBI GM Engine - high idle |
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I have a similar problem -- idle is about 1500 RPM. When I spray carb cleaner where the butterfly pivot rod exits the throttle body on the right (passenger) side, the idle drops drastically and becomes very lumpy, so I assume the bushing is badly worn.
Question: is there either a replaceable bushing in the throttle body, or possibly is there a seal? My fear is that my only option is replacing the throttle body.
Thank you in advance,
Parkerea |
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