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MY 1992 GMC TBI 5.7 IDLE PROBLEM

 
gnomepunter
I love my Chevy Chevette!
Posts: 6
Joined: 03/10
Posted: 03/29/10 10:20 AM

ok lol first off i have recently fixed my egr code and my temp sensor code issues they were causing my truck to not accellerate right and lag badly .well now my ecm isnt throwing any codes (using paperclip) on the port but my truck will not idle when cold i have messed with the timing and the iac and the idle screw on the throttle body but no matter what i do it still dies on cold idle unless i hold the gas down for like 20 or 30 seconds then it runs like new well not like new it still has a very slight skip every few seconds i have noticed a very small leak under the front of intake manifold.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 03/29/10 03:54 PM

first off....    copy and paste this link in a new window..

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/6a/large/0900c15280067e6a.gif

then print the chart...   just looking at it will help you understand..


now... with the engine off...  climb up so you can reach the throttle lever...   open it slightly...    see if it wiggles around..   excessive play in the throttle shaft bore will cause the throttle position sensor to come to a stop at different voltages almost every time you take your foot off the gas pedal...    this confuses the computer as it never knows when you actually have your off the gas...  so it never knows when to start the idle program of fuel control....

now... you are not really supposed to be adjusting the idle stop screw...    with the air cleaner spacer rings off...   take a shop rag.. stuff it with a screw driver in the odd shaped hole behind the passenger side throttle bore...  this blocks the idle air bypass so you can set base idle...   base idle should be about 500 rpms...  there should be no  or almost no leakage around the shop rag stuffed into the cavity..   once the engine is idling at 500 rpms to 600 rpms..  you can pull the rag...

if you had a run away fast idle problem... put the thermostat back in..  or a new one.. 195F please... the last number of the part number should be a XXXX9 to indicate a 192/195F...

what.. why...?????      the engine coolant temp has to come up at expected increments.. and get over 185 for the fast idle to really come down.. if the engine coolant temp sensor does not show that temp... the ECM will command the IAC.. idle air control motor to back out and try to warm the motor..    this is just how gm designed it...

if your engine coolant temp sensor, connector or pigtail is bad..  it may signal the ecm that the engine temp is -20F...

that will usually turn on the check engine light..   but not always...

print out the chart...    find someone with a scan tool... write your actual readings on the chart.. so you can compare them..    look at ECT...  TPS     IAC...  IAT...    

if the base idle is correct.. the idle air counts will be somewhere between 20 and 50... i know the chart says 5 and 50... but i did not print that..      TPS voltage that is different every time you close the throttle is going to cause you problems..

most better equipped carb shops can rebush the throttle body.. take it apart.. NOT THE THROTTLE BLADES>>  take the fuel injector pod off the top..  this will let them just have the throttle base...  be sure to ask if they do it.. not all do..

i have sent a few units in complete.. gotten them back with cleaned injectors.. and the worn throttle shaft bore... saying the injectors were dirty.. and the throttle shaft was OK...

if you are really handy.. i know how to rebush it..  not that hard...

ask for instructions ..  it takes a while to type them out..  

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 03/29/10 03:54 PM

Welcome, gnomepunter (LOL good one)

The issues you mention are consistent with a leaking intake manifold. I'd do an intake gasket job.  
idrivejunk

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 03/29/10 04:18 PM

i may have overshot the situation.. and i drive junk is probably right.. change the leaking intake manifold gaskets..

i only wanted you to check the throttle shaft play...

with a scan tool.. you can tell if the IAC is backing out for cold start.. it should come back between 90 and 130 for a cold start..

when you do have the intake off.. examine the reluctor in the distributer... make sure the magnet is not cracked..  

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 03/29/10 04:21 PM

Naw hell wayne we just posted at the same time... I was laffin  Laugh yers is better  
idrivejunk

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gnomepunter
I love my Chevy Chevette!
Posts: 6
Joined: 03/10
Posted: 03/29/10 05:26 PM

hmmm odd i just went an unplugged my temp sensor on the top front of my intake manifold and it cleared up entirly it runs amazingly now hmmm odd ill just replace the dam thing  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 03/29/10 08:52 PM

you might also want to change the connector and several inches of the wires...

at AZ

Duralast / Connector - Coolant Temp Sensor
For your 1992 Chevrolet Truck C2500 3/4ton P/U 2WD 5.7L TBI 8cyl
Part Number: 254  

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gnomepunter
I love my Chevy Chevette!
Posts: 6
Joined: 03/10
Posted: 03/30/10 07:46 AM

ok new issue i just noticed when my truck is running and i turn on my radio (factory radio) it has this squeling noise to it and the harder i push the gas the louder the noise gets im thinking a bad ground maybe?  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 03/30/10 06:45 PM

bad ground.. loose antenna... loose ground on the fender where the antenna is mounted...

could also be a bad alternator..   some chain stores have a roll out alternator tester... they can check for AC voltage on the battery circuit..

when the alternator diodes go bad.. it will put out AC voltage instead of nice clean DC..   you can also measure it with a digital volt meter..  on AC... at the battery post..

you might really want to verify the fender where the antenna is mounted is properly grounded..


there is also a possibility that the  harness in the HEI unit has started to go bad...  it goes from the 2 pin side of the module to the 3 wire connector on the side of the distributer cap./.. its a small possibility...  

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idrivejunk
I mow my lawn and find Chevys
Posts: 5119
Joined: 12/09
Posted: 03/31/10 03:46 AM

The wrong kind of spark plugs can also cause radio noise, at least in the older rides.  
idrivejunk

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 03/31/10 01:28 PM

i just had a friend replace his ignition coil...  he was complaining about lack of power and misfiring...  he found a big crack in the coil...   when he changed it..  the car ran great.. and the radio noise he never complained about vanished also..

i had forgotten about using a portable radio and waving the antenna over a running motor to find noise producing areas...  

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