Throttle Position Sensor (TPS) issue

[Tan_Van]

Just replaced the Throttle Position Sensor due to fluctuating RPMs at constant speed.

Replacing the TPS fixed this issue, but now the van idles at 1200 rpm. The TPS change was the only fix. Could this be a bad TPS or are some TPS's calibrated slightly differently (Auto Zone purchase). As far as I can tell the TPS was installed properly? Anything else to check to change idle setting?

Thanks,

[Renegade1127]

They 'should' all be the same.

The throttle body can cause idling problems as well. Make sure it is clean - just use electrical contact cleaner or brake cleaner - and pay particular attention to any carbon/dirt build up on the edges of the throttle plate (butterfly valve) which can stop it seating properly. Whatever you do, don't try to scrape any gunge off or you will leave scratches which allow air past.

[Matt86]

Did you disconnect the battery when you changed it? I found that on Chryslers, and may other cars, when replacing a TPS or IAC, disconnect the battery so the vehicle can re-learn it's settings.

[Tan_Van]

Sorry for the delay. site wouldn't let me post after 1st message.

After driving the van on three trips, it seemed to learn the TPS. Now idles down correctly. Maybe I should have disconnected the battery immediately.

Unfortunately the original problem returned. Between 45 and maybe 55, flat road, constant throttle, the engine starts varying about 200 rpm maybe once a second.

Tonight I am going to clean the throttle body and butterfly valve. Anything else to look for? Engine service light is OFF.

Thanks for the help.

98 T & C LXi, 3.8L, about 180K miles.

[Tan_Van]

OK I cleaned the throttle body and valve. Didn't make a difference.

Happens at about 45 and at about 55, constant throttle, flat road. I believe it happens at 45 when not in overdrive and 55 when in overdrive.

What else can cause rpms to change at about once a second? Anywhere from 200 to 400 rpm difference.

A previous car (GM) had these exact symptoms, and the mechanic changed out the TPS and the air mass sensor. Always thought it was the TPS. Trying not to have to take it into the shop

Thanks,
Tan_Van

[jgbat]

Trying not to have to take it into the shop

Thanks,
Tan_Van

I do understand you not wanting to take it to the shop, but be careful. You already bought one part that was not needed. I see customer's all the time that bring there vehicle in, tell me the grocery list of parts they have replaced, and they are finally bringing it to be looked at. If your not careful you can waste a lot of money throwing parts at the problem when if you had just took it somewhere and had it diagnosed properly, you'd be cheaper in the long run... even after paying the shop.

Did you take the throttle body off when you cleaned it? Did you remove and clean the IAC and the path for the IAC inside the throttle body?