Discussion:
Uneven idle
(too old to reply)
Hank
2007-04-28 20:50:18 UTC
Permalink
I got a 85 GT last summer 63K miles it has never really ran that good
in my opinion where as the idle runs from 700 to 1000 up and down. It
can also be felt while driving the uneveness at a steady speed of say
35 or 40 mph. While checking the timing it also is not steady at all
bouncing from 10 to 7 deg TDC. Is this normal or what should I be
looking for. I tried changing the 02 sensor, TPS, MAP I have a donor
car to swap parts from. I replaced the wires cap rotor and plugs.

I have an 85 SE as well 2.5 runs great I know all about the 4 cyl
keeping it running good but not as familar with the 6 cyl in the GT.

Thanks
Hank
Les Benn
2007-04-30 05:31:45 UTC
Permalink
check a few things, 1 vacuum leak...go buy a boat load of bulk hose and
replace what looks old or cracked (real cheap fix sometimes) 2) EGR is
filled with crud clean all the carbon out that might make it not work right
or get a new EGR and still clean out the crud
Post by Hank
I got a 85 GT last summer 63K miles it has never really ran that good
in my opinion where as the idle runs from 700 to 1000 up and down. It
can also be felt while driving the uneveness at a steady speed of say
35 or 40 mph. While checking the timing it also is not steady at all
bouncing from 10 to 7 deg TDC. Is this normal or what should I be
looking for. I tried changing the 02 sensor, TPS, MAP I have a donor
car to swap parts from. I replaced the wires cap rotor and plugs.
I have an 85 SE as well 2.5 runs great I know all about the 4 cyl
keeping it running good but not as familar with the 6 cyl in the GT.
Thanks
Hank
Hank
2007-04-30 23:59:51 UTC
Permalink
I took off the EGR tonight it was pretty clean but I cleaned it up it
appears to working correctly. After reinstalling it the engine was
cold so I started it up all ran very smooth but after a few minutes
after it reach temp it was like a switch was trown the RPM droped down
to and then strated fluxuating up and down between 700 and 1000 Rpm's.
The vacuum hoses appear to be in pretty good shape I replaced one the
other night that broke off by accident. Also there are no stored codes
and I tried last month swapping the ECM but it ran the same.

I was having a problem last year it was stalling at stop signs and you
could hear additional rumbling in the exhust when down shifting so I
swaped out the IAC which corrected the stalling and reduced the noise
but maybe it need a new IAC. I did clean out the IAC port of the
carbon and set the IAC plunger height before installing it.
Hank
Post by Les Benn
check a few things, 1 vacuum leak...go buy a boat load of bulk hose and
replace what looks old or cracked (real cheap fix sometimes) 2) EGR is
filled with crud clean all the carbon out that might make it not work right
or get a new EGR and still clean out the crud
Post by Hank
I got a 85 GT last summer 63K miles it has never really ran that good
in my opinion where as the idle runs from 700 to 1000 up and down. It
can also be felt while driving the uneveness at a steady speed of say
35 or 40 mph. While checking the timing it also is not steady at all
bouncing from 10 to 7 deg TDC. Is this normal or what should I be
looking for. I tried changing the 02 sensor, TPS, MAP I have a donor
car to swap parts from. I replaced the wires cap rotor and plugs.
I have an 85 SE as well 2.5 runs great I know all about the 4 cyl
keeping it running good but not as familar with the 6 cyl in the GT.
Thanks
Hank
Les Benn
2007-05-01 16:38:53 UTC
Permalink
Hank the only other thing that comes to mind is the Catalytic converter
plugging up partially.

sounds to me like you have done the logical (inexpensive) stuff that I would
do.
how old is the converter?
Post by Hank
I took off the EGR tonight it was pretty clean but I cleaned it up it
appears to working correctly. After reinstalling it the engine was
cold so I started it up all ran very smooth but after a few minutes
after it reach temp it was like a switch was trown the RPM droped down
to and then strated fluxuating up and down between 700 and 1000 Rpm's.
The vacuum hoses appear to be in pretty good shape I replaced one the
other night that broke off by accident. Also there are no stored codes
and I tried last month swapping the ECM but it ran the same.
I was having a problem last year it was stalling at stop signs and you
could hear additional rumbling in the exhust when down shifting so I
swaped out the IAC which corrected the stalling and reduced the noise
but maybe it need a new IAC. I did clean out the IAC port of the
carbon and set the IAC plunger height before installing it.
Hank
Post by Les Benn
check a few things, 1 vacuum leak...go buy a boat load of bulk hose and
replace what looks old or cracked (real cheap fix sometimes) 2) EGR is
filled with crud clean all the carbon out that might make it not work right
or get a new EGR and still clean out the crud
Post by Hank
I got a 85 GT last summer 63K miles it has never really ran that good
in my opinion where as the idle runs from 700 to 1000 up and down. It
can also be felt while driving the uneveness at a steady speed of say
35 or 40 mph. While checking the timing it also is not steady at all
bouncing from 10 to 7 deg TDC. Is this normal or what should I be
looking for. I tried changing the 02 sensor, TPS, MAP I have a donor
car to swap parts from. I replaced the wires cap rotor and plugs.
I have an 85 SE as well 2.5 runs great I know all about the 4 cyl
keeping it running good but not as familar with the 6 cyl in the GT.
Thanks
Hank
Hank
2007-05-01 21:32:47 UTC
Permalink
The converter looks like it in good shape I had the whole system off
last month to replace the clutch. The guy that does the inspections
last year when it was on the lift said it did not look stock to him
from what I saw it is welded on both sides to the pipes. As to its age
no idea I got it last summer 63K miles and have put 2K addition on it
since. Like I said yesterday during warm up the idle is fine it when
it hits full warm up then it idles up and down about a 300 rpm range.
Thanks
Hank
Post by Les Benn
Hank the only other thing that comes to mind is the Catalytic converter
plugging up partially.
sounds to me like you have done the logical (inexpensive) stuff that I would
do.
how old is the converter?
Post by Hank
I took off the EGR tonight it was pretty clean but I cleaned it up it
appears to working correctly. After reinstalling it the engine was
cold so I started it up all ran very smooth but after a few minutes
after it reach temp it was like a switch was trown the RPM droped down
to and then strated fluxuating up and down between 700 and 1000 Rpm's.
The vacuum hoses appear to be in pretty good shape I replaced one the
other night that broke off by accident. Also there are no stored codes
and I tried last month swapping the ECM but it ran the same.
I was having a problem last year it was stalling at stop signs and you
could hear additional rumbling in the exhust when down shifting so I
swaped out the IAC which corrected the stalling and reduced the noise
but maybe it need a new IAC. I did clean out the IAC port of the
carbon and set the IAC plunger height before installing it.
Hank
Post by Les Benn
check a few things, 1 vacuum leak...go buy a boat load of bulk hose and
replace what looks old or cracked (real cheap fix sometimes) 2) EGR is
filled with crud clean all the carbon out that might make it not work right
or get a new EGR and still clean out the crud
Post by Hank
I got a 85 GT last summer 63K miles it has never really ran that good
in my opinion where as the idle runs from 700 to 1000 up and down. It
can also be felt while driving the uneveness at a steady speed of say
35 or 40 mph. While checking the timing it also is not steady at all
bouncing from 10 to 7 deg TDC. Is this normal or what should I be
looking for. I tried changing the 02 sensor, TPS, MAP I have a donor
car to swap parts from. I replaced the wires cap rotor and plugs.
I have an 85 SE as well 2.5 runs great I know all about the 4 cyl
keeping it running good but not as familar with the 6 cyl in the GT.
Thanks
Hank
Brian
2007-05-12 10:30:24 UTC
Permalink
The symptoms you mention seem related to the IAC. The book says to swap and
check for vacuum leaks, check fuel pressure and for water, check for
sticking injectors

My guess would be vacuum leak, since the Fiero has those plastic vacuum
lines under the intake and to the sensors, you are probably getting a faulty
reading from one of the sensors because of a leak. There is also that EGR
tube that tends to crack right under the intake manifold

An easy way to check is get some starting fluid and (sparingly) spray
different areas to see if the idle changes that is where you will find your
leak. I know its backyard but it works!!

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