Strange Throttle Response on 951
10-29-2003, 05:40 AM
#1
Racer
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Strange Throttle Response on 951
I tried doing a search on this topic but the search feature isn't working so I'm posting my question here.
Today while driving the car I got a strange jerking sensation at low speed. After driving it some more I determined that there's something wrong with the car's throttle response. Engine was cutting in and out at low speed.
The car idles fine and drives well at highway speeds. No problems there. In normal street driving is where I notice that the car doesn't want to accelerate immediately off of idle. The car stumbles at around 1500 RPM and doesn't stop stumbling until I keep the pedal floored and the RPM gets over 2500 RPM. A lot of times I have to pump the accelerator for the engine to respond. It seems like there's a dead zone between 1500 RPM and 2500 RPM.
Under and over this region the engine seems to work fine. Between this region it stumbles. The strange part is that it doesn't happen all the time. I'd say perhaps 50% of the time it stumbles.
Is it an issue with the TPS? Any other thoughts?
BTW, there hasn't been any changes or modifications to the car. Just happened literally overnight.
Thanks for all the help in advance.
*****
Today while driving the car I got a strange jerking sensation at low speed. After driving it some more I determined that there's something wrong with the car's throttle response. Engine was cutting in and out at low speed.
The car idles fine and drives well at highway speeds. No problems there. In normal street driving is where I notice that the car doesn't want to accelerate immediately off of idle. The car stumbles at around 1500 RPM and doesn't stop stumbling until I keep the pedal floored and the RPM gets over 2500 RPM. A lot of times I have to pump the accelerator for the engine to respond. It seems like there's a dead zone between 1500 RPM and 2500 RPM.
Under and over this region the engine seems to work fine. Between this region it stumbles. The strange part is that it doesn't happen all the time. I'd say perhaps 50% of the time it stumbles.
Is it an issue with the TPS? Any other thoughts?
BTW, there hasn't been any changes or modifications to the car. Just happened literally overnight.
Thanks for all the help in advance.
*****
10-29-2003, 02:16 PM
#2
Three Wheelin'
There is a very similar type situation over on the 951 board right now, I believe. I think one area that could need checking is the AFM. I know it has a piece that drags over another and at some point once it wears away the contact in some places is can cause a faulty signal to go to the computer and get some odd changes. That or maybe the TPS is going bad and having an issue in that area would be my first thoughts.....
10-29-2003, 02:41 PM
#3
Three Wheelin'
Assumming that your car is in god tune and has no vacuum leaks, my first guess would be the TPS. If the idle switch fails in the closed position, the fuel cut-off will cause engine surging above about 1600 rpm, which sounds like your symptoms.
To test, remove the TPS plug and connect a multimeter to terminals 4 and 6 on the TPS. With the throttle closed, it should read less than 10 ohms resistance across the idle switch. When you open the throttle more than 1 degree, the idle switch should open and you should measure no connection (infinite ohms) between 4 and 6. If you continue to read a connection after the TPS clicks open or the throttle has been opened, the idle switch has failed in the closed position and is causing the problem you describe.
HTH.
To test, remove the TPS plug and connect a multimeter to terminals 4 and 6 on the TPS. With the throttle closed, it should read less than 10 ohms resistance across the idle switch. When you open the throttle more than 1 degree, the idle switch should open and you should measure no connection (infinite ohms) between 4 and 6. If you continue to read a connection after the TPS clicks open or the throttle has been opened, the idle switch has failed in the closed position and is causing the problem you describe.
HTH.
10-29-2003, 04:02 PM
#5
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I'd check the vacuum hoses for leaks/cracks. At higher RPMs, a leal may not affect the system and at low RPMs the vacuum is negligable, so the range you're talking about may allow enough a vacuum leak to cause significant and intermittant inputs.
10-30-2003, 02:59 AM
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Racer
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Hey guys,
Thanks for all the feedback and debugging techniques. I'll give all the ideas a shot this weekend and see if it'll fix the problem.
Actually when I first encountered this problem the other day my initial thought was the reference sensors. One of the two sensors has a cracked plug so it could become loose. When I got to thinking more about this it wasn't right. When you unplug any of the reference sensors the engine just dies, not stumbles, just goes dead; so it couldn't be the reference sensors.
Vacuum leaks, TPS, AFM should be a good start!
*****
Thanks for all the feedback and debugging techniques. I'll give all the ideas a shot this weekend and see if it'll fix the problem.
Actually when I first encountered this problem the other day my initial thought was the reference sensors. One of the two sensors has a cracked plug so it could become loose. When I got to thinking more about this it wasn't right. When you unplug any of the reference sensors the engine just dies, not stumbles, just goes dead; so it couldn't be the reference sensors.
Vacuum leaks, TPS, AFM should be a good start!
*****