Idle problem
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On The Tree
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From: Texas
Idle problem when i turen my car on it idles at 1000rpm then it will just go up to 1200 and some times it wil go up to 1400 it will do that some times then it will just be fine...why does it do that what can it be... it only does that when the car is in neutral ...it has a lt4 hot cam and it has an msd box can it be one of those or can if be the maf ...the car runs fine i just dont like it to idle like that.
Is it tuned? Any codes?
Usually high idle is caused by a vacuum leak or a faulty IAC. I would hook up a vacuum gauge and check around for leaks. You can unplug your MAF, and see if your symptoms go away. If it does, then your MAF or connection to it is bad.
Usually high idle is caused by a vacuum leak or a faulty IAC. I would hook up a vacuum gauge and check around for leaks. You can unplug your MAF, and see if your symptoms go away. If it does, then your MAF or connection to it is bad.
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From: Decatur, TN (N-W of Athens)
If the car doesn't run w/o the MAF then I'd say you also need a MAP sensor (pass side of the intake behind the TB), but that shouldn't cause your problems. I'd say either an IAC like SS said or check your TPS.
Give us some details about your car, year, transmission etc.
Give us some details about your car, year, transmission etc.
Thread Starter
On The Tree
Joined: Feb 2009
Posts: 163
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From: Texas
the year is 1995 its a 6 speed it has full boltons cam and all msd parts ...well the car runs good when im driveing but now at idle the car just drops to 500 and then terns off and some times it will just go up and down 1000 to 1200 when the car is at a stop or when im idling .. but ill try to get a new MAP sensor and see if thats it but i dont want to wast money on some thing i dont need so if you all think its that let me know then ill get it thanks for the help
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From: Decatur, TN (N-W of Athens)
the year is 1995 its a 6 speed it has full boltons cam and all msd parts ...well the car runs good when im driveing but now at idle the car just drops to 500 and then terns off and some times it will just go up and down 1000 to 1200 when the car is at a stop or when im idling .. but ill try to get a new MAP sensor and see if thats it but i dont want to wast money on some thing i dont need so if you all think its that let me know then ill get it thanks for the help
And I'd look into your IAC and TPS before the MAP, but I'd still get one. If you have ANY other GM vehicle that's older than like 95, it should have the same MAP. Oh, and isn't boosted (super ala 3800s or turbo ala Sy/Ty)
The MAP is anything but a fallback device. MAF measures the volume of air entering the engine while the MAP, in short, measures load. The PCM also used MAP values to determine when to activate and deactivate the EGR solenoid. Additionally it tells the PCM where to look in the fuel and ignition timing tables. High MAP = high engine load. Low MAP = low engine load.
The MAP is a very simple device and rarely goes bad. The PCM is very apt at determining the MAPs functionality, setting code 33 or 34 if the voltage is outside acceptable tolerances (roughly between 1.0v to 4.8v, may differ from car to car).
I would check your vacuum again, with a vacuum gauge. Low manifold vacuum doesn't need to happen from a hose being off. I would suspect your IAC as well. Additionally, intermittent gremlins like you mention with your idle speed are often the cause of faulty or broken wiring.
You still haven't mentioned if you've gotten any trouble codes either. Have it scanned and pull the stored codes, then disconnect the PCM/BAT fuse for a minute or two and scan it again when the idle issue arises.
The MAP is a very simple device and rarely goes bad. The PCM is very apt at determining the MAPs functionality, setting code 33 or 34 if the voltage is outside acceptable tolerances (roughly between 1.0v to 4.8v, may differ from car to car).
I would check your vacuum again, with a vacuum gauge. Low manifold vacuum doesn't need to happen from a hose being off. I would suspect your IAC as well. Additionally, intermittent gremlins like you mention with your idle speed are often the cause of faulty or broken wiring.
You still haven't mentioned if you've gotten any trouble codes either. Have it scanned and pull the stored codes, then disconnect the PCM/BAT fuse for a minute or two and scan it again when the idle issue arises.
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From: Decatur, TN (N-W of Athens)
The MAP is anything but a fallback device. MAF measures the volume of air entering the engine while the MAP, in short, measures load. The PCM also used MAP values to determine when to activate and deactivate the EGR solenoid. Additionally it tells the PCM where to look in the fuel and ignition timing tables. High MAP = high engine load. Low MAP = low engine load.
No ones really ever gone in depth on them in any of the threads I've read. What little has been mentioned was limited to the conversion to SD and that if you're not tuned, you can run off just it but since the VE tables are so lacking in the factory MAF tune, you won't really have any performance running just off it. More of just a limp-home feature. And actually, after re-reading what he said, I thought it sputtered and died. Didn't noticed it idled fine after MAF being unplugged.
So if it idles weird with the MAF plugged in, then fine unplugged, I would go with what RamAir said about faulty wiring. With the MAF plugged in and a fairly stable idle, wiggle the wires around behind the plug and then down the harness further. If the car reacts while doing that, then it's a fair bet one or more of the wires are cracked and partially broken or broken inside the sheathing, making intermittent connections causing erratic signals to the PCM.
