Hi,
I have a pre-facelift ST220 with 315kkm on the dial but swapped engine for a 120kkm one.
The car is de-cat (already bought like that) so I have lambda spacers on the post-cat lambdas
to keep the ECU from producing a emission system error.
Ever since I bought the car, I had a strange problem with idle. It goes like this:
- When I start the engine cold, it keeps higher revs until it warms up and everything is fine
- When I start the engine warm, it revs from the starting and then the RPM would normally drop to the idle value
But on my car, it drops lower, sometimes 0.7, sometimes as low as 0.4, and after like a half of second, the engine
sort of "remembers" that it should keep the idle RPM and the revs get up to the idle value and stay there.
- The same behaviour is when I park for example, or in any scenario, where I rev the engine and then take of my leg
off the gas pedal - as soon as I do that, the revs drop lower then they should, and after a split of a second they
pick up to the normal value
At first I thought idle valve, right? So I swapped it for a scrapyard one, didn't help. I thought I might have bought
a bad one so I just ignored this and it's been like this for 3 years now.
However, this is not the main problem I am having and am only mentioning it because now I feel the problems might
be connected. The main problem is this:
- When the engine is in low RPM (under 2k) and I put the gas pedal down significantly, the engine stutters. It's not
the usual low-rpm stutter which is sort of regular, this is like a random misfiring or something like that, feels like it is
randomly losing power or as if I was randomly tapping the break pedal.
- It usually goes away as soon as the engine revs over 2k RPMs, but couple of time it also happened over 2k.
I took the car to a service and they changed the following:
- Spark plugs
- Spark cables
- Air filter
- Fuel filter
It didn't help. I googled a little and found a lot of results about bad TPS sensor. I had been having problems
with the TPS sensor during the winter (revs not going back to idle when in neutral) so I bought a second hand
TPS sensor as well as another idle valve (second one now). Changed both. The revs not comming back to idle
was solved, but not the stutter.
I also remember that previous owner replaced injection on the old engine that broke down and I kept it when I
was replacing the engine so I had the service swap the injections for me. It didn't help.
So now I am completely in the dark. To me it seems like two possibilities:
1) Spark coil
2) Random worn wire shorting to ground
I have a diagnostic tool with both OBD and J1850-PWM modes so I can read a lots of values from lots of units.
If there is something I can check to find out what is the cause, I can test it myself. I also have a working knowledge
of electricity, and a multimeter so that's also something I can do myself.
Please let me know, the car is sort of drivable with this but it's such a nuisance when accelerating from full stop.
I also feel like it's less powerful than it was.
Thanks everyone for any help.
Andy
I have a pre-facelift ST220 with 315kkm on the dial but swapped engine for a 120kkm one.
The car is de-cat (already bought like that) so I have lambda spacers on the post-cat lambdas
to keep the ECU from producing a emission system error.
Ever since I bought the car, I had a strange problem with idle. It goes like this:
- When I start the engine cold, it keeps higher revs until it warms up and everything is fine
- When I start the engine warm, it revs from the starting and then the RPM would normally drop to the idle value
But on my car, it drops lower, sometimes 0.7, sometimes as low as 0.4, and after like a half of second, the engine
sort of "remembers" that it should keep the idle RPM and the revs get up to the idle value and stay there.
- The same behaviour is when I park for example, or in any scenario, where I rev the engine and then take of my leg
off the gas pedal - as soon as I do that, the revs drop lower then they should, and after a split of a second they
pick up to the normal value
At first I thought idle valve, right? So I swapped it for a scrapyard one, didn't help. I thought I might have bought
a bad one so I just ignored this and it's been like this for 3 years now.
However, this is not the main problem I am having and am only mentioning it because now I feel the problems might
be connected. The main problem is this:
- When the engine is in low RPM (under 2k) and I put the gas pedal down significantly, the engine stutters. It's not
the usual low-rpm stutter which is sort of regular, this is like a random misfiring or something like that, feels like it is
randomly losing power or as if I was randomly tapping the break pedal.
- It usually goes away as soon as the engine revs over 2k RPMs, but couple of time it also happened over 2k.
I took the car to a service and they changed the following:
- Spark plugs
- Spark cables
- Air filter
- Fuel filter
It didn't help. I googled a little and found a lot of results about bad TPS sensor. I had been having problems
with the TPS sensor during the winter (revs not going back to idle when in neutral) so I bought a second hand
TPS sensor as well as another idle valve (second one now). Changed both. The revs not comming back to idle
was solved, but not the stutter.
I also remember that previous owner replaced injection on the old engine that broke down and I kept it when I
was replacing the engine so I had the service swap the injections for me. It didn't help.
So now I am completely in the dark. To me it seems like two possibilities:
1) Spark coil
2) Random worn wire shorting to ground
I have a diagnostic tool with both OBD and J1850-PWM modes so I can read a lots of values from lots of units.
If there is something I can check to find out what is the cause, I can test it myself. I also have a working knowledge
of electricity, and a multimeter so that's also something I can do myself.
Please let me know, the car is sort of drivable with this but it's such a nuisance when accelerating from full stop.
I also feel like it's less powerful than it was.
Thanks everyone for any help.
Andy