High Idle Half the time.

[goblazers_6]

I have a 92 b3 105,000 on the clock 5 sp

Half of the time it idles at 1500 rpms. why?!

also I am only getting 35mpg and i've done everything i can to lighten the car. new plugs wires oil and air filter and gutted the cat with proper tire inflation. what else should i check or do?

[stefan]

dose it idle high even when warm? make sure your throttle cable isnt sticking and leaving the t-body cracked open. if all else fails you can adjust it down.

FYI others have reported that gutting your cat kills back pressure which messes up something with the motor (cant remember off hand, a simple search should pull it up... ) and it reduces torque and gas milage.

[goblazers_6]

idles high even when warm. and at seemingly random times. and i kept the stock muffler and exhaust but my cat was pretty clogged so it may or may not be a temp fix but since i did it i went from 33 to 35 mpg.

[donna]

Had a friend that had the same problem, found the TPS was bad, may or may not be the same problem as yours tho.

[phantorn]

What about when you push in the clutch when getting off the interstate?
Might not want to lower the idle to much if it only happens 1/2 the time.

[monkeyracing]

Check the idle air bypass valve. If it gets gummed up, or just plain worn out, it can cause symptoms like this. X2 on the throttle position sensor, and sticky throttle cable.

[jglutz]

dose it idle high even when warm? make sure your throttle cable isnt sticking and leaving the t-body cracked open. if all else fails you can adjust it down.

FYI others have reported that gutting your cat kills back pressure which messes up something with the motor (cant remember off hand, a simple search should pull it up... ) and it reduces torque and gas milage.

All engines love less back pressure. However the O2 sensors don't... lower back pressure will result in a lean feedback thus cylcling the injectors more.

Reset the idle (not the throttle screw) but the screw under the black cover. Requires a special jumper. Post if more instruction is required.

[goblazers_6]

more instruction is needed

[FB71]

the Throttle Posistion Sensor (TPS) on these cars is very rudimentary. Its basically two switches, one for closed throttle and one for wide open. Typically, the closed throttle switch contacts become worn, and no longer make proper contact. Without the switch showing closed, the PCM (powertrain control module, also called and ECM or ECU) will keep the rpms a bit higher, in anticipation of a load. I suspect your TPS is bad.

[goblazers_6]

cost of a new one?

[FB71]

around $80

[jglutz]

Setting the idle:
1) Warm the engine up...at least on cooling fan cycle. Park or nuetral and nothing on or running.
2) If you don't have a tach connect one to the engine. The other sigle connector flapping in the wind near the ignition coil.
3) Connect a wIre between the STI connector and the negative post on the battery. The STI connector is a single connector hanging out of the harness between the ignition COIL and brake booster. It is a yellow wire with a dark trace (I don't remember, black or green).
4) Remove the black rubber cover from the throttle assemby....top front right side
5) Adjust the screw as necessary. In (CW) to reduce RPM...Out (CCW) to increase RPM.
6) After completion...it is best to...check the timing..Post if additional detail is required.
7) Cover the idle screw and remove the jumper...You're done.

WARNING....NEVER ADJUST THE THROTTLE STOP SCREW...IF YOU TURN THE SCREW IN....THE VAF WILL PICK UP THE ADDITIONAL AIR FLOW AND NEITHER THE IDLE SCREW (PREVIOUS) NOR THE IAC WILL BE ABLE TO CONTROL RPM. IF YOU TURN THE SCREW OUT...YOU'LL DAMAGE THE THROTTLE BODY BORE AND THROTLE PLATE AND NOT BE ABLE TO CONTROL IDLE RPM.

[goblazers_6]

where is my throttle position sensor? and is it a bad idea to get one from a junkyard?

[FB71]

its the black box, about half the size of a pack of cigs, one the side of the throttle body. If you cand a low mileage car, you might get lucky. Otherwise, buckle under and buy a new one.