IAC/TPS troubles
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Joined: Dec 2000
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From: Raleigh, NC, USA
IAC/TPS troubles
I went to look at my TPS yesterday and unplugged it.. and SNAP! went the clip. growl. It stays plugged in just fine, but it was an annoyance... So then I go to look at the IAC connector and SNAP! goes that clip too. grr. ANYways...
I put the paperclip in terminals A & B, set the key to the "on" position, waited for a while, but when I went to disconnect the IAC stepper motor it was making a clicking noise, like it either wasn't done moving or it was trying to keep moving when it shouldn't. I unplugged it anyways, because I waited about 2 minutes and figured it was fully extended.
I turned the screw to get the idle speed down, but I couldn't get it any lower than 500 rpm's. The screw wasn't even touching the throttle linkage anymore, there was about a millimeter gap between the throttle linkage and the screw housing.. whatever it's called. *shrug*. I thought it might be the cruise control cable being too tight so I disconnected that.. no different. Then I tried to push the linkage back by hand.. but it wouldn't budge. So I just set it to about 500 rpm's.. Everything works, and the idle is MUCH smoother now.. so I guess it's fine.. I'm just curious as to why I couldn't get it to go any lower than 500 rpm.
On another note, I think I pushed the throttle linkage back too far: When I started the car this morning the throttle was suck closed.. I had to push the gas reeeaaally hard to get it to release.. It was fine most of the day after that, but once at a stoplight I pumped the gas hard for a second just to rev it up, and when I went to take off it got stuck again. Barked the tires when I finally got the pedal to move. I guess I'm fortunate it didn't get stuck in the WOT position. hehe Is there anything I could easily eyeball to make sure I didn't bend anything to make it stick like that?
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89 iroc-z 305 tbi
k&n filtercharger, open element air filter. nuffin' else
I put the paperclip in terminals A & B, set the key to the "on" position, waited for a while, but when I went to disconnect the IAC stepper motor it was making a clicking noise, like it either wasn't done moving or it was trying to keep moving when it shouldn't. I unplugged it anyways, because I waited about 2 minutes and figured it was fully extended.
I turned the screw to get the idle speed down, but I couldn't get it any lower than 500 rpm's. The screw wasn't even touching the throttle linkage anymore, there was about a millimeter gap between the throttle linkage and the screw housing.. whatever it's called. *shrug*. I thought it might be the cruise control cable being too tight so I disconnected that.. no different. Then I tried to push the linkage back by hand.. but it wouldn't budge. So I just set it to about 500 rpm's.. Everything works, and the idle is MUCH smoother now.. so I guess it's fine.. I'm just curious as to why I couldn't get it to go any lower than 500 rpm.
On another note, I think I pushed the throttle linkage back too far: When I started the car this morning the throttle was suck closed.. I had to push the gas reeeaaally hard to get it to release.. It was fine most of the day after that, but once at a stoplight I pumped the gas hard for a second just to rev it up, and when I went to take off it got stuck again. Barked the tires when I finally got the pedal to move. I guess I'm fortunate it didn't get stuck in the WOT position. hehe Is there anything I could easily eyeball to make sure I didn't bend anything to make it stick like that?
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89 iroc-z 305 tbi
k&n filtercharger, open element air filter. nuffin' else
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Enkil,
Your throttle plates will continue to bind in the closed position until you use the adjusting screw to get them open, even if only just slightly. If you don't repair this soon, you can damage the throttle body. You need to repair this.
The IAC will continue to try to step down as long as the ALDL jumper is in position and the ignition is turned ON. This is normal. The ALDL has no internal feedback device to the ECM. The ECM tells it when to open and close based on engine RPM, and it will continue to try to close or open even when it's at the end of its travel. This normally won't cause any harm to the IAC.
One possible reason that the idle would not go any lower is that the IAC valve pintle was not sealing well. If you haven't already done so, you might want to remove the IAC and clean the pintle and the seat inside the throttle body IAC opening. You should also clean the IAC air passages as best you can while the IAC is removed. Reset the IAC pintle all the way open, then install it in the throttle body. Try the adjustment again. If it still doesn't lower below 500RPM without having the throttle plates fully closed, you may have a vacuum leak somewhere.
NOTE: This vacuum leak can also be a PCV valve. I had a cheap POS Fram aftermarket PCV do this to me once, and it was brand new. After I almost pulled my hair out chasing the problem, I reluctantly replaced the new PCV with another new PCV, this time with an AC that was designed for the car. Problem solved.
The vacuum leak could be a hose, sticky EGR, loose throttle body, plenum/runner bolts loose, internal leakage of the brake booster, worn TB shaft, leaky injector 'O' rings, etc. If you disconnect and cap all the vacuum hoses and still have a high RPM, you might have a gasket leak. However, I'm guessing you won't have to go that far to find the problem.
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Later,
Vader
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"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
Your throttle plates will continue to bind in the closed position until you use the adjusting screw to get them open, even if only just slightly. If you don't repair this soon, you can damage the throttle body. You need to repair this.
The IAC will continue to try to step down as long as the ALDL jumper is in position and the ignition is turned ON. This is normal. The ALDL has no internal feedback device to the ECM. The ECM tells it when to open and close based on engine RPM, and it will continue to try to close or open even when it's at the end of its travel. This normally won't cause any harm to the IAC.
One possible reason that the idle would not go any lower is that the IAC valve pintle was not sealing well. If you haven't already done so, you might want to remove the IAC and clean the pintle and the seat inside the throttle body IAC opening. You should also clean the IAC air passages as best you can while the IAC is removed. Reset the IAC pintle all the way open, then install it in the throttle body. Try the adjustment again. If it still doesn't lower below 500RPM without having the throttle plates fully closed, you may have a vacuum leak somewhere.
NOTE: This vacuum leak can also be a PCV valve. I had a cheap POS Fram aftermarket PCV do this to me once, and it was brand new. After I almost pulled my hair out chasing the problem, I reluctantly replaced the new PCV with another new PCV, this time with an AC that was designed for the car. Problem solved.
The vacuum leak could be a hose, sticky EGR, loose throttle body, plenum/runner bolts loose, internal leakage of the brake booster, worn TB shaft, leaky injector 'O' rings, etc. If you disconnect and cap all the vacuum hoses and still have a high RPM, you might have a gasket leak. However, I'm guessing you won't have to go that far to find the problem.
------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now..."
Adobe Acrobat Reader 4.0
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Joined: Jul 2000
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From: Kempner,TX,
Car: 1996 Vette / 1992 GSX1100F Suzuki
Engine: 1996 Corvette Coupe 388 LT1 (+.060)
Transmission: Auto
Axle/Gears: 3.07
I came across a GM Tech Bulletin some time back for the minimum idle speed to be set at 550 RPMs instead of 450 which is in their service manual, (at least it's in mine.)
There was no reason listed for the change, but it could be a result of just what you're experiencing. If you back out the TB torx screw enough trying to get 450, the butterflies stick.
If I remember correctly, someone posted it on the Corvetteforum.com site.
Using Diacom or a ScanTool if your IAC counts are 25 or slightly less, closed loop at idle, it's set correctly.
Don't forget to check the TPS voltage after any adjustments to the minimum idle speed. Changing minimum idle also changes TPS voltage.
BTW, AutoZone sells replacement IAC and TPS connectors that you can just splice into your harness. Cheap too.
Jake
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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9
There was no reason listed for the change, but it could be a result of just what you're experiencing. If you back out the TB torx screw enough trying to get 450, the butterflies stick.
If I remember correctly, someone posted it on the Corvetteforum.com site.
Using Diacom or a ScanTool if your IAC counts are 25 or slightly less, closed loop at idle, it's set correctly.
Don't forget to check the TPS voltage after any adjustments to the minimum idle speed. Changing minimum idle also changes TPS voltage.
BTW, AutoZone sells replacement IAC and TPS connectors that you can just splice into your harness. Cheap too.
Jake
------------------
1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9
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