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Quoted From dreamer2355:
Is this only happening when you have the cruise control on?
If so, i would recommend sweep testing the TPS with a DVOM.
no, it happens with or without cruise control. It only happens when I am coasting ( no throttle input )
I would definitely check out the TPS to see if it is working properly. TPS’s are potentiometers and if they get old and corroded inside it will screw up the voltage reading to the computer and make the car think the throttle is more open than it actually is.
I would still go ahead and sweep test the TPS for any flat spots.
I would suspect an issue with the IACV but only if the idle was ‘loopy’ at per se a stop light.
Did you do a visual inspection to see if there is any damage to any vacuum hoses?
And i don’t suppose you have access to a scan tool that shows PID data do you?
Quoted From Cameron92:
It depends how fast I am going, Ill get another video, but when im crusing at 110km/h it bounces from like 1500-900 rpm constantly and only if I have my foot off the gas. I dont feel the car surging or anything. The rpms are just bouncing.
I just want to make sure I’m reading this right. Does the engine actually seem to be changing speeds? Or is it just that the tach needle is bouncing around?
How many rpm’s is the tach jumping ? do you feel an actual surge/drop in the engine idle at that speed ? are you using a cruise control when this issue occurs ?
your video never showed. you will need to find out how your engine is reading the rpm. its going to be a sensor,crank or cam position sensor. the sensor
is probably weak. I would suggest using the forum search to free Chilton manuals and locate that sensor.good luck and keep us posted.Quoted From 619DioFan:
How many rpm’s is the tach jumping ? do you feel an actual surge/drop in the engine idle at that speed ? are you using a cruise control when this issue occurs ?
It depends how fast I am going, Ill get another video, but when im crusing at 110km/h it bounces from like 1500-900 rpm constantly and only if I have my foot off the gas. I dont feel the car surging or anything. The rpms are just bouncing.
Is this only happening when you have the cruise control on?
If so, i would recommend sweep testing the TPS with a DVOM.
Quoted From dreamer2355:
I am assuming those number were with KOEO?
Most TPS readings should be around 0.9v idle and 4.9 WOT.
Does this have the 3.8 SC motor?
There was a TSB for fuel pump delivery issues due to a ballast resister they used.
And you say your issue is only evident on deceleration? No problems at all at idle or acceleration?
Yes KOEO. I just checked google and thats right around what most people see at idle (In these motors)
Yes it is the 3.8 3800 S/C (L67)
Yes only evident on deceleration. No issues whatsoever with idle or acceleration.
http://www.youtube.com/user/briansmobil … XBogMCgIvY
Seeing as you have ruled out the TPS, i would be inclined to look at the IACV. The best way of testing those is with a bi-directional scan tool.
Did you ever do a power balance test?
Is this issue also present if you load the engine with the brakes applied?
Quoted From dreamer2355:
http://www.youtube.com/user/briansmobil … XBogMCgIvY
Seeing as you have ruled out the TPS, i would be inclined to look at the IACV. The best way of testing those is with a bi-directional scan tool.
Did you ever do a power balance test?
Is this issue also present if you load the engine with the brakes applied?
Not sure what a power balance test is..
Now that I think about it, when I apply the breaks, the revs will stay up around 2000 (depending on how fast I am going) for a bit then it will go back to bouncing between 900 and 2000 (depending on speed)
http://www.youtube.com/user/EricTheCarG … AOmUjAjNjE
Above is the power balance test by Eric.
I would suggest you may have an ignition system issues but, you do not have any issues on acceleration. Ignition faults are usually found under a load.
I would like to see scan tool data to and view the fuel trims as well as IACV position when this issue is present.
Did you check your throttle linkage?
Do you have any way of testing your IACV?
Quoted From dreamer2355:
I would still go ahead and sweep test the TPS for any flat spots.
I would suspect an issue with the IACV but only if the idle was ‘loopy’ at per se a stop light.
Did you do a visual inspection to see if there is any damage to any vacuum hoses?
And i don’t suppose you have access to a scan tool that shows PID data do you?
I do have a scangauge and i also noticed that my ignition timing changes as the RPM’s bounce, I have also looked at the TPS input on my scangauge as the rpms are jumping and there is no change in the reading, it stays at 0. I read somewhere that it could possibly be the TCC solenoid not allowing the car to go into overdrive. I have checked all vacumn hoses and they all seem to be in good condition.
Quoted From dreamer2355:
http://www.youtube.com/user/EricTheCarG … AOmUjAjNjE
Above is the power balance test by Eric.
I would suggest you may have an ignition system issues but, you do not have any issues on acceleration. Ignition faults are usually found under a load.
I would like to see scan tool data to and view the fuel trims as well as IACV position when this issue is present.
Did you check your throttle linkage?
Do you have any way of testing your IACV?
I will try the power balance test tomorrow.
The throttle cable has no slack and is tight.
I will get my scangauge to read fuel trims, but im not sure if it can read IACV position.
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