Off throttle problem?
05-07-2005, 07:46 PM
#1
Drifting
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Off throttle problem?
Well, I have noticed this problem with my car and I am tring to track it down. What happens is that when I am driving and let off the gas (still in gear) that the motor's RPMs come down but doesn't come down smooth. It almost feels like a backfire like every 3 - 5 seconds. At speed, idle, full power, it all feels normal and good only when slowing down.
Now, work I JUST did before this happened. I put in all new vacuum lines, here is where I noticed that one of the lines was off. The line that was off was RIGHT before the intake manifold on the bottom side, so when I put in new lines, I plugged that in. I also had to take off the AFM sensor to get that line in but I checked that and still seems to work fine. I also then reset the idle because it was a little higher then stock after the lines put in.
What I am thinking is that it COULD be the AFM on there but I really don't know what else to look for or what it could be. I have checked all the lines, still good and all the way on. I vacuum is actually better then before, it was about 16 when hot, now I am getting about 18-19 hot at idle. So, what should I be looking at and how do I test to see if it is good? Side note, I have a cat-bypass in the car as well. Thanks.
Now, work I JUST did before this happened. I put in all new vacuum lines, here is where I noticed that one of the lines was off. The line that was off was RIGHT before the intake manifold on the bottom side, so when I put in new lines, I plugged that in. I also had to take off the AFM sensor to get that line in but I checked that and still seems to work fine. I also then reset the idle because it was a little higher then stock after the lines put in.
What I am thinking is that it COULD be the AFM on there but I really don't know what else to look for or what it could be. I have checked all the lines, still good and all the way on. I vacuum is actually better then before, it was about 16 when hot, now I am getting about 18-19 hot at idle. So, what should I be looking at and how do I test to see if it is good? Side note, I have a cat-bypass in the car as well. Thanks.
05-08-2005, 11:57 PM
#4
Defending the Border
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That was my suggestion. I rebuilt the throttle body with the Arnnmorks kit and had to pay special attention to the TPS.
BTW, two of the three throttle shaft o-rings were in little pieces, the third must have been combusted at some point.
BTW, two of the three throttle shaft o-rings were in little pieces, the third must have been combusted at some point.
05-09-2005, 03:34 AM
#6
Race Director
"What happens is that when I am driving and let off the gas (still in gear) that the motor's RPMs come down but doesn't come down smooth. It almost feels like a backfire like every 3 - 5 seconds."
"Found the problem, the TPS wasn't clicking when it would close. So I re-adjusted and all good now!"
"clicking when closing? mine clicks when openning... bad? do I just rotate it?"
It clicks as it opens and clicks as it closes. This is a binary switch that tells the DME whether the throttle is open or closed. When it's closed, the DME switches to the idle fuel-maps and cuts off the fuel above... 2000rpm or so. If however, the switch isn't connected properly, the DME thinks you've got the throttle open and it uses the partial-throttle maps, which does have fuel above 2000rpm. Which is the source of your popping and surging.
If you monitor the AFM's voltage under closed-throttle deceleration, you'll see that the flapper door oscillates back & forth... probably some harmonic pulsations going back and forth. This would trick the DME into injecting fuel for air-flow that's not really occuring.. thus the pops and stumbles. Better to just cut off the gas altogether when you're coasting...
"Found the problem, the TPS wasn't clicking when it would close. So I re-adjusted and all good now!"
"clicking when closing? mine clicks when openning... bad? do I just rotate it?"
It clicks as it opens and clicks as it closes. This is a binary switch that tells the DME whether the throttle is open or closed. When it's closed, the DME switches to the idle fuel-maps and cuts off the fuel above... 2000rpm or so. If however, the switch isn't connected properly, the DME thinks you've got the throttle open and it uses the partial-throttle maps, which does have fuel above 2000rpm. Which is the source of your popping and surging.
If you monitor the AFM's voltage under closed-throttle deceleration, you'll see that the flapper door oscillates back & forth... probably some harmonic pulsations going back and forth. This would trick the DME into injecting fuel for air-flow that's not really occuring.. thus the pops and stumbles. Better to just cut off the gas altogether when you're coasting...
