1990 Riviera poor idle

I have a 1990 Buick Riviera with a 3800 v6 that has a slight idle problem. Here is the scenario. At idle in park the car had a rather decent mis to it. I checked the codes and got code 48, which is a misfire symptom. Ok, i already knew that. I check all the wires and plugs and found out that the #4 plug wire was arcing off on the O2 sensor wire. So i changed plugs and wires both. being that i just got the car i thought it to be a good idea to do that anyways. Ok, that cured the misfire that i once had. But, this car has a very poor idle, almost like it is lopping. The idle is about 800 RPM like it should be. But it will not keep a good idle at all. it will fluctuate badly from about 500 RPM's to about 800 RPM's and vice - versa. I have checked the codes again and all is well not a single code at all. I have checked the TPS and it seems to be just fine. I can move the lever and it will stop doing what it does, this is still while in park. I adjusted the TPS to not do this anymore and all seems ok until i put it in reverse or drive or anything other than park or neutral. The problem comes back. Should i replace the TPS with the factory one, even though i am not getting a code. Or could it even possibly be in the coil. I know it is something minor, just thought i would ask some advice of the good people here at this site. Thanks in advance.

How do you adjust a TPS ??

How do you adjust a TPS ??
It is adjustable. The best way is to use a digital vom . engine off. unplug tps harness. there are three wires going to it. connect vom to the outer two wires (ignition on). voltage should be about 0.5 at idle. open throttle voltage should be about 4. as you open the throttle the voltage should increase smoothly. to adjust loosen the two set screws and turn the tps left or right.

I have a 1990 Buick Riviera with a 3800 v6 that has a slight idle problem. Here is the scenario. At idle in park the car had a rather decent mis to it. I checked the codes and got code 48, which is a misfire symptom. Ok, i already knew that. I check all the wires and plugs and found out that the #4 plug wire was arcing off on the O2 sensor wire. So i changed plugs and wires both. being that i just got the car i thought it to be a good idea to do that anyways. Ok, that cured the misfire that i once had. But, this car has a very poor idle, almost like it is lopping. The idle is about 800 RPM like it should be. But it will not keep a good idle at all. it will fluctuate badly from about 500 RPM's to about 800 RPM's and vice - versa. I have checked the codes again and all is well not a single code at all. I have checked the TPS and it seems to be just fine. I can move the lever and it will stop doing what it does, this is still while in park. I adjusted the TPS to not do this anymore and all seems ok until i put it in reverse or drive or anything other than park or neutral. The problem comes back. Should i replace the TPS with the factory one, even though i am not getting a code. Or could it even possibly be in the coil. I know it is something minor, just thought i would ask some advice of the good people here at this site. Thanks in advance.
Does the idle stutter when you tap on the mass airflow sensor with something like a screwdriver handle?

I have a 90 buick Riv as well and i have the same exact problem in neutral or park it idles fine but in drive it lopes. Might just be a factory problem.

I have a 90 buick Riv as well and i have the same exact problem in neutral or park it idles fine but in drive it lopes. Might just be a factory problem.


I would remove, clean and replace the IAC. Reattas have this same problem.

Enjoy
FlyByNite