TPS resulting in high idle ???
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 1,094
Likes: 68
From: Providence RI
TPS resulting in high idle ???
All,
1991 m6
Been battling various issues but a new one popped up the other day right after I got a new reman ECM which fixed my ccm codes.
While driving above 70 or so, I'd put it in neutral to coast and the idle would stay at 1800 rpms. Later on in the trip, it was fine and would drop to 750-800. Again later on, it acted up. CEL lit up, then went off, no codes stored. Came to a stop light, engine died. Immediately restarted and ran fine the rest of the way home.
The TPS was new around June of last year...doesn't mean it isn't junk. I can't remember where I bought it from in order to return for warranty claim. I still need to check to make sure it isn't loose and moving around.
I have not hooked up Datamaster in order to double check anything, just wanted to see if a bad TPS could cause the high idle speed?
The throttle body is new and in great shape, the butterfly is closing all of the way while this is happening.
Thanks,
Mike
1991 m6
Been battling various issues but a new one popped up the other day right after I got a new reman ECM which fixed my ccm codes.
While driving above 70 or so, I'd put it in neutral to coast and the idle would stay at 1800 rpms. Later on in the trip, it was fine and would drop to 750-800. Again later on, it acted up. CEL lit up, then went off, no codes stored. Came to a stop light, engine died. Immediately restarted and ran fine the rest of the way home.
The TPS was new around June of last year...doesn't mean it isn't junk. I can't remember where I bought it from in order to return for warranty claim. I still need to check to make sure it isn't loose and moving around.
I have not hooked up Datamaster in order to double check anything, just wanted to see if a bad TPS could cause the high idle speed?
The throttle body is new and in great shape, the butterfly is closing all of the way while this is happening.
Thanks,
Mike
Melting Slicks
Joined: Jan 2001
Posts: 2,996
Likes: 304
From: MOORESVILLE NC
TPS can cause high and too low idle. Can also cause the engine to shut down while sitting in traffic. Even after all that, the TPS will function as it should and will not throw a code. I had issues similar on another GM vehicle. As a last ditch effort I bought a cheap TPS, $15, off ebay. Solved my idle. Prices ranged form 15 to 62$ off ebay.
Drifting
Joined: Mar 2013
Posts: 1,952
Likes: 239
From: Venice Cali.
TPS can cause high and too low idle. Can also cause the engine to shut down while sitting in traffic. Even after all that, the TPS will function as it should and will not throw a code. I had issues similar on another GM vehicle. As a last ditch effort I bought a cheap TPS, $15, off ebay. Solved my idle. Prices ranged form 15 to 62$ off ebay.
It looked ok but screwed my idle all up.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
While driving above 70 or so, I'd put it in neutral to coast and the idle would stay at 1800 rpms. Later on in the trip, it was fine and would drop to 750-800. Again later on, it acted up. CEL lit up, then went off, no codes stored. Came to a stop light, engine died. Immediately restarted and ran fine the rest of the way home.
When you do data log, check the IAC numbers when you come to a stop.
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
My tps sensor went bad a few weeks ago and high idle was the first symptom. Wife and I were going thru a drivethru and the idle shot up to 1800 or so and wouldn't come back down. Then after a few minutes it dropped down. We got our food and pulled around and parked. After a few minutes sitting there listening to the radio the idle shot up again. I cut the car off and checked for a weak return spring or something or a vacuum leak and zilch. So we headed on to our next stop. Driving down the road with the cruise on it suddenly lost power. From that point on it did nothing under 1/4 pedal. With the 383 motor and 3.73 gears that trip home was "interesting" to say the least having to keep the pedal pushed down a 1/4. My vettes brakes were no match for that motor and rear end combo.
Anyways after getting home and hooking up the hand scanner it confirmed what I was guessing on the tps sensor and had a code for it to best I remember. One interesting thing was after the car cooled off it was fine again but I changed the sensor the next day anyways. Alls fine now.
So short version, yes the tps sensor can cause idle to go nuts and idle high.
Anyways after getting home and hooking up the hand scanner it confirmed what I was guessing on the tps sensor and had a code for it to best I remember. One interesting thing was after the car cooled off it was fine again but I changed the sensor the next day anyways. Alls fine now.
So short version, yes the tps sensor can cause idle to go nuts and idle high.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 1,094
Likes: 68
From: Providence RI
Okay so I fixed it. The tps was the cause but it wasn't bad. I replaced it a year ago.
The arm on the tps was binding against the throttle body when things got hot. I ohmed out the tps and it went through the range fine.
I noticed a mark on the throttle body and the arm of the tps. I filed down the arm a little, reinstalled, and test drove 40 miles without issues.
So the throttle was closing but the tps stayed open just enough to tell the computer to give more fuel while the aic made up for the lack of throttle body airflow.
When the tps did finally return, that caused the cel and the car to stall at idle because it was getting all confused.
Sound right?
Thank you all.
Mike
The arm on the tps was binding against the throttle body when things got hot. I ohmed out the tps and it went through the range fine.
I noticed a mark on the throttle body and the arm of the tps. I filed down the arm a little, reinstalled, and test drove 40 miles without issues.
So the throttle was closing but the tps stayed open just enough to tell the computer to give more fuel while the aic made up for the lack of throttle body airflow.
When the tps did finally return, that caused the cel and the car to stall at idle because it was getting all confused.
Sound right?
Thank you all.
Mike
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Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 413
From: WV
If you were going 70 mph on the highway and shifted into neutral, then your motor did exactly what it was suppose to do by keeping the rpms up around 1800 rpm...Can you imagiing what would happen if your rpms dropped to around 650 rpm in neutral at that speed , then you pulled the transmission back into drive at 70 mph..
.. My rpms only start dropping in neutral when my speed starts dropping.This is because of the ( throttle follower mode) and decay that Cliff mentioned above, which keeps the rpms higher in neutral, when the car speeds are higher...If the system wasn't set up like this , there would be alot of blown transmissions around....WW
.. My rpms only start dropping in neutral when my speed starts dropping.This is because of the ( throttle follower mode) and decay that Cliff mentioned above, which keeps the rpms higher in neutral, when the car speeds are higher...If the system wasn't set up like this , there would be alot of blown transmissions around....WW
Last edited by WW7; May 1, 2015 at 05:52 AM.
Thread Starter
Burning Brakes
Joined: Mar 2010
Posts: 1,094
Likes: 68
From: Providence RI
You're right, but it was never a quick drop to idle. It would stay at 1200ish then drop once stopped. 1800 to 2k was too high. It was like using cruise control, the car would actually gain speed depending on gear and how fast I was going.
Thanks
Thanks
Drifting
Joined: Sep 2014
Posts: 1,579
Likes: 59
From: Trieste Italy
If you were going 70 mph on the highway and shifted into neutral, then your motor did exactly what it was suppose to do by keeping the rpms up around 1800 rpm...Can you imagiing what would happen if your rpms dropped to around 650 rpm in neutral at that speed , then you pulled the transmission back into drive at 70 mph.... My rpms only start dropping ,when my speed starts dropping.This is because of the ( throttle follower mode) and decay that Cliff mentioned above, which keeps the rpms higher in neutral, when the car speeds are higher...If the system wasn't set up like this , there would be alot of blown transmissions around....WW
.. My rpms only start dropping ,when my speed starts dropping.This is because of the ( throttle follower mode) and decay that Cliff mentioned above, which keeps the rpms higher in neutral, when the car speeds are higher...If the system wasn't set up like this , there would be alot of blown transmissions around....WW
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 413
From: WV
. .The ecm makes sure you don't tear out your trans by monitoring your speed, then not letting the rpms drop down to the point where it would damage the motor or trans when you pulled it back into gear...
...WW
Last edited by WW7; May 1, 2015 at 06:26 AM.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 413
From: WV
I understand now, glad you figured it out, if you hadn't noticed the tps arm on the TB was sticking you may have never gotten it fixed..WW
Drifting
Joined: Sep 2014
Posts: 1,579
Likes: 59
From: Trieste Italy
What I'm saying is at highway speeds if you shift into neutral , your rpms shouldn't drop straight down to idle..Your rpms should only drop down a small amount , so when you pull the transmission back into gear at that high speed, your not pulling it into gear on an engine doing only 650 rpms ..This would be like going down the highway in 6th gear with a stick shift at 70 mph, pushing in the clutch, shifting into 2nd gear, then poping the clutch . .The ecm makes sure you don't tear out your trans by monitoring your speed, then not letting the rpms drop down to the point where it would damage the motor or trans when you pulled it back into gear......WW
. .The ecm makes sure you don't tear out your trans by monitoring your speed, then not letting the rpms drop down to the point where it would damage the motor or trans when you pulled it back into gear......WW