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throttle body problems

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Bobby62G

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I own a 1990 k5 and I get 7mpg around town. it seems to idle about 1500rpm. how can I lower the idle and could this be part of the reason of such poor mpg? I live in ca. an it just passed smog so I think it's in tune somewhat.I am running 33x12.50's so I don't expect stellar milage, maybe 10 though. Thanks Bobby
 
try a new TPS sensor, (Throttle position sensor) they're usually only a couple bucks at the local parts store
 
mpg

what mpg should I expect? had the k5 2 mos. 5.7 ,400r , 33x12.50's pretty stock with flowmaster and k&n filter. I really like this truck but my 74 fj 40 gets more than twice the 7 mpg around town. Thanks 1990 full size
 
high idle could be a vacuum leak, the throttle body gaskets on those are common for leaking ...
 
There is definatly something wrong. Unless you have a heavy foot you should be getting better than 7 MPG.
Check the base TB base gasket as said above. Also all the vaccum lines.
When was the last time it was tuned up, and the fuel filter changed? Any trouble codes?
Does the check engine light come on?

I get 15 mpg average city/ highway commuting driving no problem in my 89 K5. But i dont live in a big city where I sit in traffic and idle a lot.
I am lifted and on 33s ,350, 700r4, 3.73 gears, headers, flowmaster, ect
 
Yeah i would def check out your vac lines. then if there all fine i would check your intake gasket and the tbi gasket. (with the motor running spray some carb cleaner around the intake and listen to see if it idles up, if so you have a leak. also do around the tbi)
 
I will check this out today. thanks for the tips, I really like this truck but gas is 3.40 a gallon in San Francisco
 
I forgot that when driving at freeway speeds for 15 min or so it throws a service engine light untill I turn it off for awhile. on the freeway I get 11 mpg just 7 around town
 
As stated check Vacuum lines and for leaks around the TBI, Check to make sure the Line to the MAP is not cracked, It is usally cracked where it connects to the MAP. Check the wiring to the MAP and also the IAC make sure the connectors are seated well.
Do you have or access to a scanner?
It sure would help to know what the code is.
I would replace the gasket on the base of the TBI, Cheap and easy to do. Less than $3 bucks at NAPA.

How dirty is your TBI,, Look at your IAC port (Back left side) is it full of soot, dirt etc.. With the key on engine off look down the port to see if you can see the pintle of the IAC. Start the motor, do you have a load hissing sound coming from the IAC port? Plug the IAC port with your finger. Does the idle come down?

Do not mess with the idle adjustment!!!!! It is plugged for a reason. I do have the proper procedure for adjusting if needed. But I think your problem is vacuum or IAC related. Bad IAC and MAP or Vacuum will cause you to run rich and poor MPG.

Pull a plug to see what it looks like. Is it black and sooted up?
 
If your CEL is coming on You really need to check the trouble codes. It may be a code that puts the ECM is bypass or "Limp Home Mode" If that is happening, usually it will run rich. With only enough timing advance to run the engine. That will kill your gas milage.
Here's how to check the codes and what they mean: http://www.troublecodes.net/GM/
The data link is under the dash by the steering column. Check the codes and post them up.
 
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