Variable idle speed: simple tune up tip

fljeeper

fljeeper

TJ Enthusiast
Joined
Feb 7, 2016
Messages
138
Location
Bradenton, Florida
I just want to pass on this tip. My 98 4.0 five speed had variable idle speeds since I bought it about two years ago. I tried the usual IAC cleanng several times with temporary results. When I accelerated hard the exhaust smelled like catalytic converter. When stopped, the idle might be 700 to 1000 RPM's. With the A/C on it would idle at 1100 RPM's when the compressor was engaged. I then installed a new throttle position sensor (TPS) and all of these symptoms have been eliminated. Now, no matter what, it always idles at the same speed, about 700 RPM's. A few minutes work and a much better running vehicle. If you think about how the TPS works, you will understand why they wear out. I wonder if there is a reccomended service interval for the TPS.
 
  • Like
Reactions: ac_, Chris and sinatranate
My wife’s Jeep was doing the same thing, but the TPS didn’t fix it. So far, it has new plugs, new IAC valve, new Crank sensor, freshly cleaned throttle assembly and air intake, and still bucks and idles high around 1250-1500 rpm. Anybody have any other ideas?


Sent from my iPhone using Tapatalk
 
Very nice, thanks for sharing this. Typically when the TPS goes bad, you should get an error code for it. The FSM doesn't have a recommended replacement interval for the TPS (or any sensors for that matter as far as I know). However, everything goes bad in time!
 
sinatranate said:
My wife’s Jeep was doing the same thing, but the TPS didn’t fix it. So far, it has new plugs, new IAC valve, new Crank sensor, freshly cleaned throttle assembly and air intake, and still bucks and idles high around 1250-1500 rpm. Anybody have any other ideas?


Sent from my iPhone using Tapatalk
Click to expand...
Use a vacuum gauge to check for vacuum leaks. Also make sure your header and the rest of the exhaust is sound.
 
  • Like
Reactions: sinatranate
Chris said:
Very nice, thanks for sharing this. Typically when the TPS goes bad, you should get an error code for it. The FSM doesn't have a recommended replacement interval for the TPS (or any sensors for that matter as far as I know). However, everything goes bad in time!
Click to expand...

Since the TPS has parts that physically rub against each other, it is different than allot of other sensors, and because friction is involved, these parts will wear out and cause inaccurate signals to the computer.
 
  • Like
Reactions: Chris
fljeeper said:
Since the TPS has parts that physically rub against each other, it is different than allot of other sensors, and because friction is involved, these parts will wear out and cause inaccurate signals to the computer.
Click to expand...

Yes, that actually makes perfect sense.
 
Top Bottom
Back