5.7 TBI - high idle

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EdontheBeach

Master Mechanic
Feb 29, 2012
278
176
43
Indian Rocks Beach, FL
fellas - i have an 83 cutlass cruiser with a 92 350 TBI from a roadmaster. if i drive at anything over about 30-35mph, when i come to a stop the engine continues at a high idle (1200-1300) for 30 or 40 seconds after i stop before settling down to 750rpm. i've checked the gas cable and don't feel it hanging up. any idea what might be the culprit? this is my first TBI car, i don't know where or what to look for.
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
Check your idle air sensor on the TBI. There is a setting procedure, it may just need replaced. I think your Avatar is a bit too much.
 

tc1959

Comic Book Super Hero
Dec 23, 2009
3,963
1,975
113
Surprise AZ.
Three things can cause what you are describing.
1. A worn throttle shaft, This can be repaired by having new bushings installed at a Carb shop.
2 the TPS or throttle position sensor is faulty or misadjusted. You need a DVOM to set it properly.
3 The Idle Air Control motor or IAC for short is faulty or clogged up with carbon. This is the most likely cause of the high idle. It is located on the side of the T-Body and is very easy to replace. it just screws in. It's a good idea to clean the port with some carb spray before installing the new one. Also disconnect your battery for 3-5 minutes to reset the computer and let the car sit and idle for ten minutes so the computer can relearn the idle.


I have no idea what a idle air sensor is. I have never heard that one before. :?
 

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gwhiz

Greasemonkey
Aug 21, 2012
184
0
0
clean the entire throttle body ou real good.i had a 91 tbi that was so gummed up the throttle plates would stick every once and a while.if that dont work look at iac valve.luckily all the sensors on that motor are cheap
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
Well sorry couldn't remember IAC :roll: . I kept thinking IAT, which I knew was wrong. Either way right part, wrong name. Clean out the passage really good as mentioned.
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
Very cool. Your Avatar as a joke was fine :). The TBI is a very good set up.
 
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