96 lumina rough idle at start

[Ranger Larry]

I have just changed throttle body from the 52mm to a 56mm. When i got back on and started 3 times now the car has a lopey idle. Once alittle warm it stops but rpms are about 100-150 higher. Does anyone have a suggestion to problem or could it be something i miss installed.

[SappySE107]

Usually a bad sensor will do this. Did you reuse the TB gasket or get a new one?

[Ranger Larry]

I replaced the IAC and got a new gasket and found a vacuum line that goes from PCV to throttle and behind motor loose. I reattached line and Rpm went back to normal. When the motor is started cold it kind of acts like its not getting enough air. If i touch throttle alittle and get rpms to 1000 to get it alittle warm its ok then. I'm beginning to think i just need to adjust the throttle screw on TB. What do you suggest? The Throttle position sensor has not been replaced. Should i replace also? Other than that the car runs more responsive and feel a power gain and using less gas.

[SappySE107]

The screw on the throttle body is just a stop screw and should not be adjusted. If the ECM learned the IAC position from having the vacuum leak, it may take some time for it to learn that it needs more IAC steps than before. I would run it for a while and see how it works out.

[Ranger Larry]

Thats what i thought also it could take about 100 miles to straighten out. Also there was a thing that fell either off or was on floor already when i tapped out the shaft of TB. It was like a metallic o-ring. Could that go to TB SENSOR?

[robertisaar]

The screw on the throttle body is just a stop screw and should not be adjusted. If the ECM learned the IAC position from having the vacuum leak, it may take some time for it to learn that it needs more IAC steps than before. I would run it for a while and see how it works out.

or pull the negative cable off of the battery or pull the PCM fuse. those tricks still work with obd2, right?

[SappySE107]

That ring was just in place for the shaft and doesn't go back on when you swap shafts. I deal with that on the billet throttle bodies so I know it isn't necessary.

I don't know how long the OBD2 computer keeps its memory. OBD1 is basically instant once it loses power.