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97 Ford Taurus GL 3.0 OHV AX4N
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I have a 97 taurus vulcan at 120k miles. Rpm will randomly jump to anywhere between 1000 and 2000, usually it jumps to about 1600 but it can be higher or lower. This is all while it's in park. It'll jump from regular of 800 to 900 to the above mentioned. In drive, if I let off the brake from a stop it'll sit at about 1200 without hitting the gas pedal. Now before anyone says IAC, I'm not completely ruling that out tho either, the iac in it is about a year and a half old. It is a motorcraft one, the electrical connector is about 2 months old (I replaced this because the latching part of it had snapped off). After initial replacement of the iac the problem had disappeared for about a year, plug was broken entire time, then the problem returned. After i replaced plug, the problem was gone for about a week. And now more recently I took the sensor off and cleaned it, replaced gasket, and cleaned the MAF. Problem was gone for a day and then returned. Lol it's driving me crazy. To temporarily cure the problem I'll go out and unplug then replug the iac and it'll return to normal for anywhere from 5 minutes to an hour. This used to only happen about once a day but now it's sporadic, anywhere from once a day to 10 times. Also worth mentioning, if I just let it go, the car will eventually unrev and go back to normal.

It seems this has gotten worse since it started getting colder out, also now that I think about it, this doesn't seem to start until car has reached operating temperature. I've looked for vacuum leaks but I haven't really tested for them other than watching fuel trims which stay close to zero cold or hot engine.

Anyways, why I'm wondering tps. Today I was watching values on my scan tool. At regular idle, tps is about 16 percent, which I've seen as normal elsewhere in the forum. But once it decides to rev, tps jumps to 21 percent. Long term fuel trim then jumps to about +8 on both banks, short term becomes sporadic jumping between -5 and +5. So I then unplugged iac while watching tps percent, it drops back to 16 percent with iac unplugged and then stays at 16 once plugged back in.

Another reason I think tps, when engine is hot and I start it. Occasionally it will instantly sputter and die unless I hit the gas and hold it at about 2000 rpm for about 10 or 15 seconds.

Sorry for the long post, this is my first post and I figured the more information the better.

I'm currently replacing pcv valve and grommet. I'ma see if that helps any, then if not, I'm considering using seafoam spray to clean throttle body and whatever else the spray reaches to see what happens.

Thanks for the help.
 

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Have you tried looking at TPS % with key on, engine off while exercising the throttle? Much easier than doing it with the engine running. TPS isnt too expensive and is easy to replace, so I would start there. Use ONLY the Motorcraft part. Most aftermarket parts from the discount parts stores are JUNK. Rock Auto will be cheaper than getting one at your friendly (not) Ford dealer.
 

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In 25 years of owning these cars and over one million miles of experience I have never had a TPS cause an idle issue, Only issue was a dead spot in in the throttle respond which I could see using a ohm meter to see an non linear increase on resistance. Looking at the TPS % is a good idea or look at the IAC values to see if it is actually changing or is it just a vacuum leak.
 

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I have a 97 taurus vulcan at 120k miles. Rpm will randomly jump to anywhere between 1000 and 2000, usually it jumps to about 1600 but it can be higher or lower. This is all while it's in park. It'll jump from regular of 800 to 900 to the above mentioned. In drive, if I let off the brake from a stop it'll sit at about 1200 without hitting the gas pedal. Now before anyone says IAC, I'm not completely ruling that out tho either, the iac in it is about a year and a half old. It is a motorcraft one, the electrical connector is about 2 months old (I replaced this because the latching part of it had snapped off). After initial replacement of the iac the problem had disappeared for about a year, plug was broken entire time, then the problem returned. After i replaced plug, the problem was gone for about a week. And now more recently I took the sensor off and cleaned it, replaced gasket, and cleaned the MAF. Problem was gone for a day and then returned. Lol it's driving me crazy. To temporarily cure the problem I'll go out and unplug then replug the iac and it'll return to normal for anywhere from 5 minutes to an hour. This used to only happen about once a day but now it's sporadic, anywhere from once a day to 10 times. Also worth mentioning, if I just let it go, the car will eventually unrev and go back to normal.

It seems this has gotten worse since it started getting colder out, also now that I think about it, this doesn't seem to start until car has reached operating temperature. I've looked for vacuum leaks but I haven't really tested for them other than watching fuel trims which stay close to zero cold or hot engine.

Anyways, why I'm wondering tps. Today I was watching values on my scan tool. At regular idle, tps is about 16 percent, which I've seen as normal elsewhere in the forum. But once it decides to rev, tps jumps to 21 percent. Long term fuel trim then jumps to about +8 on both banks, short term becomes sporadic jumping between -5 and +5. So I then unplugged iac while watching tps percent, it drops back to 16 percent with iac unplugged and then stays at 16 once plugged back in.

Another reason I think tps, when engine is hot and I start it. Occasionally it will instantly sputter and die unless I hit the gas and hold it at about 2000 rpm for about 10 or 15 seconds.

Sorry for the long post, this is my first post and I figured the more information the better.

I'm currently replacing pcv valve and grommet. I'ma see if that helps any, then if not, I'm considering using seafoam spray to clean throttle body and whatever else the spray reaches to see what happens.

Thanks for the help.
TPS has 5.0V on one end of the rheostat, and gound=return on the other end. No physical movement of the shaft should have no change in output volts = % on the OBDII output.
In my case the % changed with no movement of the shaft only when the engine was running. See pic, the return wire goes to the lower eyelet in the pic and that is together with the primary negative power from the larger eyelet. Grounded on paint and rust in the cowl ground. Sanded the body paint, cleaned the eyelets, removed rust from the bolt. Put anti-corrosion stuff on the metals and bolted it down. Bad idle fixed. Idle speed managed by, throttle plate, IAC, and PCV. I see this ad a one time maintenance issue on old cars.
-chart-
 

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97 Ford Taurus GL 3.0 OHV AX4N
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Discussion Starter #5
Update: it's been a few days now since replacing pcv valve and grommet. Idle issues are gone! For now at least lol. But now on the flip side, I have a p0420 current and a p1504 pending :(
 

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How high is your idle speed ? Did you use a Motorcraft PCV valve or aftermarket that is letting too much air into the engine affecting idle.
 

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97 Ford Taurus GL 3.0 OHV AX4N
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Discussion Starter #7
How high is your idle speed ? Did you use a Motorcraft PCV valve or aftermarket that is letting too much air into the engine affecting idle.
I went aftermarket. Idle speed is back to it's regular 800 to 900 in park. Drives normal again.
 

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97 Ford Taurus GL 3.0 OHV AX4N
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Discussion Starter #8
Also worth mentioning the grommet I used was dormant help 42324. Real tight fit into valve cover and for pcv valve itself. Took some finessing to get it in. Used a drum brake adjustment tool as it was blunt and shouldn't tear new grommet.
 

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The pending P1504 is a idle that is too high and the idle control valve is out of it's control range I believe. You should erase the codes and see it they come back. P420 is a catalytic converter efficiency issue which is hard to blame on a current vacuum leak but any misfires in the engine previous could be the reason.
 

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97 Ford Taurus GL 3.0 OHV AX4N
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Discussion Starter #10
The pending P1504 is a idle that is too high and the idle control valve is out of it's control range I believe. You should erase the codes and see it they come back. P420 is a catalytic converter efficiency issue which is hard to blame on a current vacuum leak but any misfires in the engine previous could be the reason.
I just checked again before I left to run some errands. P1504 had gone away on its own. I cleared p0420 and it hasn't come back yet. Just gonna keep driving now I suppose.
 
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