Rough Idle Mystery

C

Charles G

Registered User
92 SC, automatic, 3.8, ran perfectly prior to resurfacing heads due to overheat warpage. Runs well at above idle but idles rough and sometimes stalls at lights. Vacum/Boost gauge indicates about 18 of vacum at idle. Can't find any vacum leaks, Super Charger tubes are sealed perfectly, MAF sensor responds to compressed air injected toward it by shutting off engine (seems to work), IAC shuts engine down when disconnected (seems to work) could this still be problem, appears to be a popular one. Took to dealer, paid $100 for diagnostic check, no error codes and no ideas, but complimented my clean work on replacing heads, etc. I understand IAC and MAF can be bad and not produce codes... New spark plugs and wires, performs weill above idling. Putting in reverse will cause to stall. Please Help!! :confused:
 
seems to me, that maybe ur idle is too low, mines is starting to do that, i popped in my SNAP ON BEL-AIR SCANNER PRO and ran the IDLE test and got the IDLE TOO LOW...

On the throttle body there is this rubber plug, take it off and there is a allen bolt in there, if ur SC is a 5-SPEED idle should be 650 RPMS in NEUTRAL while the engine is running in normal temperature, if its a AUTOMATIC, idle speed should be at 550 RPMS in DRIVE at normal operating temperature. If you turn the allen bold clockwise u are lowering the idle, if counter-clockwise u are making it idle higher.

My car has been doing this when the needle goes upto the NORMAL position, the idle goes down to 500-490, it has died a couple of times at the stop light also, until i ran the test and found out my idle was too low at normal operating temperature. Good luck, hope it helps
 
darkstar_one said:
seems to me, that maybe ur idle is too low, mines is starting to do that, i popped in my SNAP ON BEL-AIR SCANNER PRO and ran the IDLE test and got the IDLE TOO LOW...

On the throttle body there is this rubber plug, take it off and there is a allen bolt in there, if ur SC is a 5-SPEED idle should be 650 RPMS in NEUTRAL while the engine is running in normal temperature, if its a AUTOMATIC, idle speed should be at 550 RPMS in DRIVE at normal operating temperature. If you turn the allen bold clockwise u are lowering the idle, if counter-clockwise u are making it idle higher.

My car has been doing this when the needle goes upto the NORMAL position, the idle goes down to 500-490, it has died a couple of times at the stop light also, until i ran the test and found out my idle was too low at normal operating temperature. Good luck, hope it helps
Click to expand...
Thanks, I will check it out, idle appears to be about 7 or 800 on dash tach, also going to hose clamp all vacum lines, still feels like could be a small leak....?
 
Check for body to motor ground on passanger side motor mount .Mine did the same thing yours is doing ,Bad Ground caused it . :)
 
darriantbird said:
Check for body to motor ground on passanger side motor mount .Mine did the same thing yours is doing ,Bad Ground caused it . :)
Click to expand...
Thanks, just got new motor mounts installed, is it a braided wire from block to chasis across motor mount?
 
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