Rough Idle, Stalling, need help
Thread Starter
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
Rough Idle, Stalling, need help
So yes i'm still having trouble with my '85. Hunting idle and will stall out. It stumbles on acceleration (when I can get out of the driveway). I'm trying to rule any possible problem i've missed. Heres whats been either checked or fixed so far...
No Codes
Intake Manifold - new gaskets, torqued bolts correctly this time.
No leaks in air intake
No vacuum leaks
No fluid leaks (oil, coolant, fuel)
MAF good
IAC good
Coolant sensor good
Correct fuel pressure
new fuel pump
Getting spark
New plugs, wires, cap, rotor
Timing is correct
No binding in throttle body
Battery is 1 yr old
Is there anything that I could have possibly missed that would make my car run this way? I've been through the FSM and still cant figure it out. I'm just hoping there is something I missed that someone will point out before I have to spend tons of money taking it to a mechanic.
P.S. only mods are aluminum heads w/ biggers valves (70cc combustion vs. 76cc stock) and mufflers.
No Codes
Intake Manifold - new gaskets, torqued bolts correctly this time.
No leaks in air intake
No vacuum leaks
No fluid leaks (oil, coolant, fuel)
MAF good
IAC good
Coolant sensor good
Correct fuel pressure
new fuel pump
Getting spark
New plugs, wires, cap, rotor
Timing is correct
No binding in throttle body
Battery is 1 yr old
Is there anything that I could have possibly missed that would make my car run this way? I've been through the FSM and still cant figure it out. I'm just hoping there is something I missed that someone will point out before I have to spend tons of money taking it to a mechanic.
P.S. only mods are aluminum heads w/ biggers valves (70cc combustion vs. 76cc stock) and mufflers.
Heel & Toe
Joined: May 2007
Posts: 21
Likes: 0
From: UT
I know GM does not always give a service interval for fuel filter. I recommend changing it once a year, about registration time is always good. GM is notorious for weak fuel pumps, so changing it once a year will help your pump last longer.
Le Mans Master
Joined: Feb 2006
Posts: 8,753
Likes: 9
From: Louisiana
Take the connection off the MAF sensor and look at the pins. Make sure they are clean and straight and the connection is tight. Have you clean the MAF with electrical cleaner or tested the wiring going to it? Have you checked fuel pressure while driving?
Thread Starter
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
I just replaced the pump (it lasted 113K miles by the way) but have not changed the filter, dont see how it would weaken the pump anyway. The MAF is good, all the pins are nice and straight, unplugging it has no effect on the idle.
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Safety Car
Joined: Sep 2003
Posts: 3,599
Likes: 24
From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Just to cover that base, I would fill the tank up and replace the fuel filter.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
Does this happen All the time, or just hot. Is there any difference between cold engine/underhood temps and hot? A bad coil will do this, usually it'll be fine at cold startup and go downhill as the coil heats up - within 2-3 minutes it'll be junk. You may very well NOT see this problem when checking the spark with a timing light...
Thread Starter
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
Heres an update, today I replaced the fuel filter because whether or not its the problem it most likely should be replaced anyway. However it did not help my problem. I didnt see any kinks or defects in the fuel lines at all and of course no leaks. I checked for codes again, still nothing.
As far as being out of gas, I can hold down the gas pedal and it will continue to run although not very smooth like it should. When I let off it will stall out in a few seconds. I'm sure my gauge isnt 100% accurate but I know I have gas.
The cat isnt clogged up, I just replaced it last year. And yes it happens hot, cold, whenever I just start the car. Well I cant really think of anything else to check, so any ideas?
As far as being out of gas, I can hold down the gas pedal and it will continue to run although not very smooth like it should. When I let off it will stall out in a few seconds. I'm sure my gauge isnt 100% accurate but I know I have gas.
The cat isnt clogged up, I just replaced it last year. And yes it happens hot, cold, whenever I just start the car. Well I cant really think of anything else to check, so any ideas?
Melting Slicks
Joined: Jan 2005
Posts: 2,658
Likes: 4
From: Clifton Park NY
It still sounds fuel related.
Have you thrown in just 5 gal of gas just to be sure? When at idle whats your fuel pressure? What about the fuel pressure when moving?
Your sure your timing is set? Good spark?
Have you thrown in just 5 gal of gas just to be sure? When at idle whats your fuel pressure? What about the fuel pressure when moving?
Your sure your timing is set? Good spark?
Drifting
Joined: Mar 2007
Posts: 1,295
Likes: 326
From: Central Pennsylvannia
2021 C4 of the Year - Modified Finalist
I had a similiar problem, clean the throttle body out with carb cleaner, spray both sides of the butterflies, wipe out with a rag, it wont hurt anything, and it only take a few mins, after i did it, my idle was back to normal....it might help.
Good Luck.
Good Luck.
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Unplugging the MAF should have an effect on the idle, my 85 starts idling like it's got a huge cam in it and smokes black out the exhaust when I unplug the MAF. Can you borrow another MAF somewhere?
Thread Starter
Team Owner
Joined: Feb 2006
Posts: 24,460
Likes: 7
From: sw Ohio
Unfortunately I dont know anyone else with a TPI that would let me borrow one. I'll look in the FSM and see if theres another way to test it to make sure its not bad.
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Do you know anyone who can scan your engine for you? Unless this is done, you may be buying new parts to replace good parts. I had an acceleration problem on my 89 and it turned out to be the O2 sensor and there were not any codes stored in the ECM. The O2 sensor was frozen on a certain mv value and was not jumping up/down as it was supposed to do. A scan tool quickly found this problem. Another suggestion would be to use some Chevron Techtron fuel injector cleaner and see if you have clogged injectors.