Hey guys, new here to the forums so I hope this is the right spot to
post my problems/question. I have to apologize for this long
post.



I have a 96 SL2 that has been a problem child since the day I got it,
well a few weeks later anyways. The motor blew up, which I had
replaced and tons of maintainence parts as well. The car now has
110k on it, I've just replaced the rear brake cylinders, the
starter/solinoid broke and locked up, so was replaced. Both the
front O2 sensor and the monitor sensor threw up codes last week and
were replaced.... anyways, on to the problem:



I knew that the front O2 sensor was out, because I had checked the
codes a little while earlier, when I did it, it also threw out a TPS
code. My buddy told me that the TPS code can sometimes be a false
positive because of the O2 sensor. So, anyways, my wife was
driving the car the other day after we replaced the starter and the
valve seals (which were leaking) and the car started bucking when
trying to shift and bucking a little bit at high revs/speed. It
wasn't constant, but it was something to worry about and our gas
mileage went to crap. So, I took it to my mechanic and pulled the
codes, front and rear O2 sensor. Called a buddy of mine and
talked it over with my mechanic and we decided that poor gas mileage
and occasional bucking could be caused by these parts and needed to be
replaced. Meanwhile, my wife tells me that the speedometer was
also not acting right, sometimes jumping from 40 to 80, even though she
was only going 40. I couldn't reproduce this problem and thought
it was a cable/sensor and unrelated.



Anyways, the O2 sensors are replaced and the problem of bucking
persists, although the gas mileage seems to have gone up. There
are no new engine codes. I've done a little research and I think
it could be the transmission speed sensor and cruise control amp (the
CC has always had problems since I bought the car), but I keep thinking
about that TPS code. Should I replace everything, just one thing
or am I totally off track here? Are there some tests I can do for
the speed sensor, amp or TPS? Autozone says the sensor and amp
are dealer/junkyard only.



I would appreciate any info and advice! Thanks in advance.



**Edit** The car was also shifting later than usual. This also seems to have been resolved with the O2 sensors.


Edited by: SL2ofDoom

What was the actual TPS code? (Pxxxx)

If the VSS (Vehicle Speed Sensor) is bad, it will indeed freak out your speedo in one way or another, confuse the hell out of your cruise control (since it does not know what speed you're actually going), and confuse the PCM and the transmission (and hose your shift points).

A scan tool with a real time readout of the TPS voltage would be really handy. If you don't have one, measure the V at the TPS as a buddy slowly opens the throttle. It should read about 0.4V at closed throttle and go up to 4.9V as the throttle is opened.

Please post resolution

Derf

Thanks for the reply, I'm planning on ordering a VSS next week, I was
also told to check the ECTS. I understand that it can be a
problem child with my car, but would it affect me in this way?

Btw, I don' thave the P code for the TPS, sorry, I don't have the sheet
anymore. I'm hoping it will throw another engine code now that
the O2 sensors have been replaced and the codes reset.

Well, after many attempts and several changed sensors, it turned out to
be the EGR valve. I pulled it to clean it out and when I put it
back on I noticed that it was leaking exhaust gas when I revved up the
motor, I guess it was causing a vacuum leak. Swapped it out for
my old one and so far, so good. Just thought I would let everyone
know what the fix ended up being.



Oh, the TPS and VSS are also new, they didn't fix/cause the bucking,
but the voltage was a little low on the TPS so I wanted to change it
out and the speedo probems that my wife mentioned along with a bit of a
shifting problem at high RPM prompted my mechanic to swap the VSS out.


Edited by: SL2ofDoom