1987 Monte Carlo LS 4.3 Idle Issue

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,231
658
113
Melville,Saskatchewan
#11
I am betting your mileage improved a lot as well. The other thing I was going to suggest was setting the IAC but the temp sensor fixed it, they die often.
 

FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
7
3
38
Vineland, NJ
#12
I have another issue and question. The car starts totally fine when its cold.....but randomly has a hard time starting when the engine is warm. For example if we go to the store and come back out a half hour later it won't start easily. It will be idling very low and once I rev it up a few times it starts running ok again.....almost like the engine is flooded. If I shut the car off and restart it right away it starts like it should. Any ideas?
 
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airboatgreg

G-Body Guru
Oct 2, 2016
894
559
93
60
#13
My bet is low maximum fuel pressure. Drive car until a good operating temp. Shut off and let sit for 15minutes. Try to start. If it acts crazy get it running and drive again until good operating temp. Let sit 15 minutes. Make sure radio and HVC off and turn key on....listen for fuel pump to turn on.... then off. If it doesn't you my have a bad fuel pump relay. If it does...repeat a couple three times after a 10 second or so interval. Then start and see if it runs normal. If it does you have either a fuel pump check valve bad allowing fuel to drain back to tank after hot shut down or a low max fuel pressure that is overcome by the fuel boiling in the fuel rail and the pump not able to overcome that.
 

FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
7
3
38
Vineland, NJ
#14
I had a feeling it may be a fuel pressure issue. I will have to check it out tomorrow when it is light out. I don't remember seeing any relays in the fuse panel. Would they be someplace different? Also I did change the fuel filter this morning after the car sat all night. There wasn't any fuel in the lines at all.... I was expecting some but none came out.
 

airboatgreg

G-Body Guru
Oct 2, 2016
894
559
93
60
#15
I don't remember where the relay is. But a I recall under hood and a Bosch style
 

olds307 and 403

Comic Book Super Hero
Oct 14, 2008
3,231
658
113
Melville,Saskatchewan
#16
I had that drain back issue on my 94 Z71, a new fuel pump fixed it. I would also reset the IAC, if the their isn't enough air, it can act like that. What RPM does it idle at? I ground the tamper plug and turned mine up.
 

FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
7
3
38
Vineland, NJ
#17
I had that drain back issue on my 94 Z71, a new fuel pump fixed it. I would also reset the IAC, if the their isn't enough air, it can act like that. What RPM does it idle at? I ground the tamper plug and turned mine up.
This car doesn't have a tach so I am not totally sure of the RPM's. From what I can see the IAC is open letting air in so I don't think its an air issue.
 

airboatgreg

G-Body Guru
Oct 2, 2016
894
559
93
60
#18
I had a feeling it may be a fuel pressure issue. I will have to check it out tomorrow when it is light out. I don't remember seeing any relays in the fuse panel. Would they be someplace different? Also I did change the fuel filter this morning after the car sat all night. There wasn't any fuel in the lines at all.... I was expecting some but none came out.
So still maybe a check valve issue. Try what I recommended and we will go from there
 

FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
7
3
38
Vineland, NJ
#19
I haven't had much time due to work these past few weeks and I hate working with frozen fingers so I had my mechanic check it out for me. They diagnosed it and replaced the fuel pump. I picked it up tonight. I have went out and started it a dozen times and its starts like it should....actually better than it did in the past. The car is back to normal now. Thank you guys for all the help.
 

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