need info on idle problem
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
need info on idle problem
89 auto, 50,000 miles
stock except for K&N air filter
Here is the problem
My idle wants to hang at about 1000 rpm going down the road when I put the car in Neutral no matter what the speed of my car is, until I am almost stoped, then the idle will come down to the correct idle, of around 650 rpms. It will do the same if I don't put in in neutral. When I come to almost a stop, the idle will drop down. It acts almost like a lazy IAC I have cleaned the TB and repaced the IAC several times, and have adjusted minium idle speed many times by use of the FSM. I have checked the linkage and can find no bind. Could it be the blades in the TB hanging up? If so why does the idle rpms finally drop down. The problem is like having cruse control on when driving around near 25 mph... let off of the gas, and she keeps on going.
sure could use some help
thanks
Mike
stock except for K&N air filter
Here is the problem
My idle wants to hang at about 1000 rpm going down the road when I put the car in Neutral no matter what the speed of my car is, until I am almost stoped, then the idle will come down to the correct idle, of around 650 rpms. It will do the same if I don't put in in neutral. When I come to almost a stop, the idle will drop down. It acts almost like a lazy IAC I have cleaned the TB and repaced the IAC several times, and have adjusted minium idle speed many times by use of the FSM. I have checked the linkage and can find no bind. Could it be the blades in the TB hanging up? If so why does the idle rpms finally drop down. The problem is like having cruse control on when driving around near 25 mph... let off of the gas, and she keeps on going.
sure could use some help
thanks
Mike
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
I have used fuel cleaner, have not smacked the egr. I don't know alot about the cars, but learning. I know egr could affect idle and make it idle rough. I didn't know it can hang idle if not working right. I did unhook vacuum line to egr and put vacuum on it and the engine idle started to bog Am I missing some knowledge on how the egr works? Always glad to learn more. thanks
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
its an auto. I would not mind the idle not coming down until stopped, but it hangs and acts like a cruse control, keeping the car moving at what ever speed 1000 rps will keep the car moving at. I have to use brake to slow car down until almost stopped, and then idle will come down to normal until i take off again problem over and over again
Melting Slicks
Joined: Jan 2014
Posts: 2,192
Likes: 381
From: Lunenburg MA
its an auto. I would not mind the idle not coming down until stopped, but it hangs and acts like a cruse control, keeping the car moving at what ever speed 1000 rps will keep the car moving at. I have to use brake to slow car down until almost stopped, and then idle will come down to normal until i take off again problem over and over again
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Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Sounds like the decay time for throttle follower mode is set too high. It's purpose is to keep the engine from stalling when you take your foot off the gas. It (relatively) slowly closes the IAC to reduce the idle speed to the set value. It serves the same purpose as a dashpot on a carburetor.
Has the tune been modified? You said stock, but just checking...
Has the tune been modified? You said stock, but just checking...
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
no mods except air filter
I just capped off vacuum lines from TB, both the one on the side and the one on the bottom, but it made no difference. I capped off the vacuum to gas can purge and egr. I am thinking it might be the blades sticking on the TB because sometimes it works perfect and the next time not. The idle will stick sometime near 1000 rpms and the next time 800 rmps and then the next time work perfect.
Anyone with some thoughts and knowing for sure before I spend money on new TB? Anyone know of a rebuild company ?
I just capped off vacuum lines from TB, both the one on the side and the one on the bottom, but it made no difference. I capped off the vacuum to gas can purge and egr. I am thinking it might be the blades sticking on the TB because sometimes it works perfect and the next time not. The idle will stick sometime near 1000 rpms and the next time 800 rmps and then the next time work perfect.
Anyone with some thoughts and knowing for sure before I spend money on new TB? Anyone know of a rebuild company ?
Last edited by mlm0; Sep 24, 2015 at 02:42 PM.
Thread Starter
Drifting
Joined: Dec 2012
Posts: 1,504
Likes: 73
From: Georgetown TX
I connected vacuum pump to lines and found that the plastic line that goes into firewall, will not hold vacuum. I think its the line to AC Is it suppose to hold vacuum. Also which connection on the black vacuum dirverter valve does the vacuum line from the pleium go to? Is it the one straight connection or the L shape side. Its the dirverter that controls vacuum to the AC and cruse control, and fuel purge control valve. I dont think this is my problem, because I have that complete line capped, but could be another problem. Does anyone know where that AC plastic line comes out under the inside of dash?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
It depends on what kind of HVAC system you have. On C60 (manual) HVAC systems the vacuum connects to the back of the HVAC control panel. If you have a C68 (digital) HVAC system then it connects to the HVAC programmer, which is bolted to the firewall above the gas pedal.