Won't idle down
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Freshman User
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Thanks. The only faulty reading the analyzer at O'reilly detected was the TPS. The check engine light does not come on. Cruise is OK. No problems with accelerator in any forward gear or reverse.
On this basis should I buy a new TPS or wait till I try unplugging it? One guy said a leaky intake could cause the problem. Is there any way to test the throttle linkage? I sprayed it with cleaner and it seems OK and not overly dirty or rusty.
On this basis should I buy a new TPS or wait till I try unplugging it? One guy said a leaky intake could cause the problem. Is there any way to test the throttle linkage? I sprayed it with cleaner and it seems OK and not overly dirty or rusty.
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
It would help to know what the numeric code was. We have given you tons of direction already. I suggest now, and previously, to measure what you have before tossing more $$parts$$ at the problem.
It's your truck and your choice. Follow whatever path you want to resolution.
It's your truck and your choice. Follow whatever path you want to resolution.
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I tore into it again, but could not figure out the plug on the TPS. Does it pull straight down? Is it one of those with a latch? I didn't want to proceed further for fear of damaging the plug so tried to take the TPS off with it still plugged in. That failed also as couldn't find the right wrench. Are those 5/16" heads on the two bolts? I used to have a flat little ratchet for those, but lost it and my 1/4" drive tools would not fit in. I'll try a plain box/open end after I buy one tomorrow.
Would the van be harmed by driving it with the TPS not working?
Would the van be harmed by driving it with the TPS not working?
Lead Driver
Joined: Jul 2007
Posts: 7,868
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From: Rhode Island
The bolts are metric as far as I know. TPS connector has a little pivoting latch you must press before it comes off.
It'll run without the TPS, but it will probably have poor throttle response and have trouble coming back to idle smoothly.
It'll run without the TPS, but it will probably have poor throttle response and have trouble coming back to idle smoothly.
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If metric they will be the first I have seen on the 1988 van. I will have to get a mirror to look underneath the throttle body to see the latch on the TPS plug and the bolt heads. Its all been by feel so far. Maybe I will need to remove the throttle body to get the plug out.
Where do the TPS wires go? Maybe easier to test by removing plug at other end?
Where do the TPS wires go? Maybe easier to test by removing plug at other end?
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I was able to measure the reference voltage (across black and red) at 4.88V.
I still am not able to unplug the TPS because I cannot manipulate the latch and while following ithe cable down to the wiring harness I found the red wire had a bare worn spot near the opposite plug. I made sure the bare spot was not touching any metal and started the van and problem still there.
I also have not been able to remove the TPS because I can't get a wrench on the bolt heads.
I still am not able to unplug the TPS because I cannot manipulate the latch and while following ithe cable down to the wiring harness I found the red wire had a bare worn spot near the opposite plug. I made sure the bare spot was not touching any metal and started the van and problem still there.
I also have not been able to remove the TPS because I can't get a wrench on the bolt heads.
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I guess I have been abandoned.
Does the 4.88 v ref.voltage and the 1.58 I measured between black and green on the TPS mean anything?
I still cannot remove the TPS plug or TPS. I used a dental mirror and found its mounted with Phillips head bolts, not hex heads. I have a 90-degree bent Phillips screwdriver and still can't reach the heads. Will I have to take off a bunch of hoses to get at these bolts or would it be easier to take off the throttle body?
I was looking at the throttle linkage diagram diagnosis section and it says high engine speed could be related to the Throttle Valve cable. It shows this cable going to an arm separate from the accelerator pedal. Just where is this arm in a van?
If I have to take the van into a mechanic, will it hurt to drive a few miles with the air cleaner assembly off?
Does the 4.88 v ref.voltage and the 1.58 I measured between black and green on the TPS mean anything?
I still cannot remove the TPS plug or TPS. I used a dental mirror and found its mounted with Phillips head bolts, not hex heads. I have a 90-degree bent Phillips screwdriver and still can't reach the heads. Will I have to take off a bunch of hoses to get at these bolts or would it be easier to take off the throttle body?
I was looking at the throttle linkage diagram diagnosis section and it says high engine speed could be related to the Throttle Valve cable. It shows this cable going to an arm separate from the accelerator pedal. Just where is this arm in a van?
If I have to take the van into a mechanic, will it hurt to drive a few miles with the air cleaner assembly off?
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Brett Foote
Fleet Owner
Joined: Oct 2005
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From: Kentucky
In Post #22 I listed a link to here: Ultimate Throttle Position Sensor (TPS) Thread - FSB Forums. In Post #1 of that thread it stated "THROTTLE BODY REMOVAL: In most case you will need to remove the TB to get to the TPS. First remove intake hoses and the throttle cable assembly."
Please do not get me wrong, we are trying to help you here but you are making it a little difficult. The VREF voltage you measured means your reference signal is good. The 1.58 VDC value between the TPS output and signal return means your TPS voltage at closed throttle is too high, out of range. This can be caused by someone jacking with the throttle stop screw or a faulty TPS.
Now you have to determine if the TPS is bad or the throttle is cranked open with that screw. I highly suggest you follow through and remove the throttle body for a thorough inspection. The throttle blades should just be cracked open a few degrees, anything more means someone has played with the stop screw.
Please do not get me wrong, we are trying to help you here but you are making it a little difficult. The VREF voltage you measured means your reference signal is good. The 1.58 VDC value between the TPS output and signal return means your TPS voltage at closed throttle is too high, out of range. This can be caused by someone jacking with the throttle stop screw or a faulty TPS.
Now you have to determine if the TPS is bad or the throttle is cranked open with that screw. I highly suggest you follow through and remove the throttle body for a thorough inspection. The throttle blades should just be cracked open a few degrees, anything more means someone has played with the stop screw.
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Freshman User
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Not torx that I can see. Was this head type even available in 1988?
So do my voltage measurements suggest I need a new TPS?
Not to worry about the T.V. cable?
What about the throttle linkage? Hard to take off?
Will it hurt to drive 8 miles with air cleaner off?
So do my voltage measurements suggest I need a new TPS?
Not to worry about the T.V. cable?
What about the throttle linkage? Hard to take off?
Will it hurt to drive 8 miles with air cleaner off?
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