Throttle Position Sensor

AKA Throttle Position Switch, Throttle Valve Switch (Nissan Service Manual).

What it does

The TPS tells the engine ECU when to take over idle control. When you take your foot off the accelerator, the throttle butterfly comes to the idle position, the TPS idle switch closes and the ECU starts operating the AAC valve to keep the engine idling properly. This is the only influence the TPS has on the engine ECU. If it is not closing properly, the engine will idle very poorly, or may not idle at all.

The TPS also has a switch that activates at about half throttle, and the TPS on an automatic car also has a potentiometer under the switch mechanism. The additional switch and potentiometer are used exclusively by the automatic transmission ECU.

Inside the TPS

On the left, an automatic TPS with the cover removed. It has an extra connector for the pot output. On the right, a manual TPS. Removing the cover is a destructive activity, requiring two rivets to be drilled out. You can spray contact cleaner inside the housing through slots in the bottom of the hole where the throttle shaft pokes in, and some will get on the switches, while a lot goes everywhere else. I was also considering cutting the cover just above the idle switch, scraping the switch contacts clean through the hole, then sealing the hole up again.

File:TPS 1.jpg

At idle (left) the top switch (idle) is closed, the bottom switch open. As the throttle is opened (middle), the top switch opens, the bottom switch stays open. As the throttle opens further (right), the bottom switch closes.

File:TPS 2.jpg

The TPS lives here, held on by two 7mm head bolts. The vacuum hose in the foreground is disconnected to access the lower bolt.

File:TPS 3.jpg

The TPS is adjusted by rocking it back and forth like so.

File:TPS 4.jpg

Adjustment

Nissan's Method

• 1) Start engine and raise engine speed to about 1500rpm.

• 2) Decrease engine speed and confirm that idle switch turns on at the engine speed as shown below.

Off -> On 950+-50rpm (in "N" position)

If out of specification, adjust as follows.

• 3) Disconnect AAC valve harness connector and confirm the idle speed.

650+-50rpm (in "N" position)

If out of specification, adjust by turning idle adjust screw.

• 4) Raise engine speed to about 1500rpm.

• 5) Decrease engine speed and adjust idle switch so that switch turns on at the engine speed shown below.

Off -> On 950+-50rpm (in "N" position)

• 3) Connect AAC valve connector and confirm the idle speed.

700+-50rpm (in "N" position)

My Method

(This is OK for a manual car, but probably not for an auto, as the pot position is critical for the auto operation.)

• 1) Loosen TPS retaining bolts, and start engine. Let engine idle, leave throttle in idle position.

• 2) Move TPS fully clockwise, engine will idle like shit.

• 3) Turn TPS anti-clockwise slowly until engine idles properly (i.e. switch is closed). Turn TPS a tad further, then nip up the retaining bolts, and done. (Do not lean on the bolts, as they are tiny, and they're going into aluminium, not steel.)

• Note: If the idle doesn't improve when the TPS is fully anti-clockwise, disconnect the plug, and short the top two sockets on the plug with a piece of wire or needle nose pliers etc. If the idle improves when you do this, then the TPS is faulty. Conversely if the idle still doesn't vary, the wiring to the sensor may be faulty, or a problem exists with the idle control gear (different subject), or something else again.

Compiled by: Prestagea