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98 Mystique acting strange

Tiny
SCOTTY27
  • MEMBER
  • 1998 MERCURY MYSTIQUE
  • 131,025 MILES
OK heres what going on. 2.5l v6 automatic. This just started happening, Transmission has only 20k on rebuild, So far I did a fluid flush, changed vehicle speed sensor, and idle air control valve. Its better but it will not shift or very hard when its cold out (below 35 F) once its warmed up, its perfect. Now after driving on the highway at 55-60mph rpms around 2250 for 15 minutes, the torque converter will disengage from lockup and rpms will go from 2250 to about 2700 at 55-60 mph. Try to stop and the car downshifts like a truck, not smooth at all. And try to stop and the car pushes you like your on the gas. Start to drive again and it wont shift, you have to let off the gas like your using a manual trans. Now stop again put it in neutral and rpms go about 3500. Shut the car off, put it in park, restart and you can drive away and the trans shifts like a dream until it decides to act up again. I think its electrical

Im out of ideas, im thinking of trying the transmission speed sensor and possibly the range sensor to see if thats bad. After that im lost. I cant afford a shop, I work part time but I did take it to one and there are no codes at all.

Any ideas, please help before I lose my trans or something.

Thank you,
Scott
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Tuesday, January 17th, 2012 AT 9:38 PM

37 Replies

Tiny
RIVERMIKERAT
  • MECHANIC
  • 6,110 POSTS
Take it to a shop that will scan for soft codes. These won't set the CEL. It may be a shift solenoid.
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Wednesday, January 18th, 2012 AT 8:38 AM
Tiny
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When the shop looked at it the only thing they found was the vss was bad. He said they could not find any thing else.
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Wednesday, January 18th, 2012 AT 7:34 PM
Tiny
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They told me it was some thing electrical. They said definitely a sensor.
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Wednesday, January 18th, 2012 AT 7:35 PM
Tiny
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That could do it. Incorrect signals from the vehicle speed sensor can and will make the transmission shift incorrectly.
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Wednesday, January 18th, 2012 AT 7:53 PM
Tiny
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The VSS was replaced, as well as the idle air control valve.

I am also thinking could it be the throttle position sensor or the transmission speed sensor?

Thanks, scott
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Wednesday, January 18th, 2012 AT 9:52 PM
Tiny
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I don't think it would be the TPS. Maybe the transmission range sensor or the turbine speed sensor.
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Wednesday, January 18th, 2012 AT 10:07 PM
Tiny
SCOTTY27
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  • 21 POSTS
Just got my trans speed sensor. Going to put it in and see what happens.
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Wednesday, January 18th, 2012 AT 10:38 PM
Tiny
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Ok. Let us know.
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Wednesday, January 18th, 2012 AT 11:21 PM
Tiny
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No, did not fix the problem, its worse with it in there. And the car pushes you like your pushing on the gas until you come to a complete stop. Than it downshifts from 2nd to first and everything returns to normal until you drive it again.
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Thursday, January 19th, 2012 AT 12:25 AM
Tiny
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  • 6,110 POSTS
I've asked some colleagues to peek in and see what they think.
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Thursday, January 19th, 2012 AT 4:11 AM
Tiny
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Ok thank you very much, I know this is an electrical issue, I am going to clean the plug on the top of the trans, and see what that does.
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Thursday, January 19th, 2012 AT 4:11 PM
Tiny
MHPAUTOS
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If the problem is associated with an electrical issue, it will be picked up on a scan, with the original post you say it was problematic when cold, I am wondering if you have had the line pressures checked as yet, there may be a problem with the governor or sticky valves with in the valve body, this will not set a code, but may show up as a pressure issue with a line pressure test.
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Saturday, January 21st, 2012 AT 3:01 AM
Tiny
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I cleaned the plug, trans range sensor, throttle body, and put it back together. Took the car for a ride and it ran perfect. Yay, or so I thought, today, went to work. And it started its crap again. Put it in gear and the throttle comes up and wont go back down. It like your pushing on the gas the whole time. Put it in park its fine. Put it back in gear and it acts up. Torque converter wont lockup. Unplug the battery. Try to drive the car and its fine. Something gets reset when I do that and than acts up after a while. Could it be the PCM computer?
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Saturday, January 21st, 2012 AT 9:22 PM
Tiny
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I noticed there is a box with a cable coming out of it sitting on the top of the valve cover behind the plastic shroud and it goes to something right under the throttle body. I am hearing that it is some sort of electronic throttle control for when your a/c compressor or transmission is in gear, any ideas.
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Saturday, January 21st, 2012 AT 9:27 PM
Tiny
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Ok, its not that box under the plastic shroud. Now I started the car and chocked it and put on the ebrake and I put it in gear, right away the car wanted to go, rpms came up and it pushed. I went out and disconnected the idle air control plug. And it shut off. So I adjusted the throttle body. Started the car and adjusted it until idle was at about 800 rpms (actually just looked at the rpm meter). And put it in gear, it held its own very well. Plugged the idle air back in, and immediately it began to want to take off. This is the second idle air control valve I put on this in about 3 weeks. Could this be the computer thats bad and throwing my car out of wack?
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Saturday, January 21st, 2012 AT 10:13 PM
Tiny
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It's possible. Have you checked the wiring for the IAC?
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Saturday, January 21st, 2012 AT 10:35 PM
Tiny
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That I have not done yet. It started snowing, but I did unplug and plug back in the mass air flow and everything calmed back down and when I start it and put it in gear its fine. Ill have to take it for a drive and see what happens. Im letting it get cold and will take her out tonight yet and see what happens.

Scott
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Sunday, January 22nd, 2012 AT 12:26 AM
Tiny
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Ok. Let us know. Drive safe in the snow.
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Sunday, January 22nd, 2012 AT 12:42 AM
Tiny
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Will do thank you.
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Sunday, January 22nd, 2012 AT 12:54 AM
Tiny
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Ok. It shifted fine for the first 1 mile. Torque convert lockup. Then out of nowhere torque converter unlocked and I slowed down to stop and the car was pushing again. Not shifting right. So I unplugged the idle air control valve. And adjusted the throttle body. And drove it. It was fine but no lockup. Then I stopped drove again everything perfect. Drove it for about fifteen miles some highway some stop and go. All good. Then I stopped for a light and drove again and it would not shift again. So today I unplugged the battery and reset the computer and I left the idle air control valve unplugged. Just drove it six miles. Car runs perfect, perfect shifts, perfect lockup. I dont understand it. Do you think its the computer.
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Sunday, January 22nd, 2012 AT 5:08 PM

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