1985-1998 [Subscribe to Daily Digest] |
Electronic Throttle Body (TB) Rebuild Procedure
Background – I was experiencing periodic TCS faults, characterized by sudden loss of throttle/TCS light, when depressing pedal. This was especially prevalent in hot weather. Faults could be cleared by re-starting car. I later experienced a complete inability to start car, which resulted from a stuck safety switch in the TB. Rebuild and cleaning has corrected all faults going on 6 months now.
Note – Before starting the TB rebuild, check the Throttle Position Sensor (TPS) and motor operation per Traction Control System (TCS) manual (perform the resistance checks noted). If you have a bad TPS, you probably need to get a different TB, since I don’t think you can find sources for the TPS. You may be able to clear a safety switch fault (see 9) below.
Pins Function Reading (ohms) 1/7 Motor <200 throughout range 2/6 TPS 900-1200 2/4 TPS 5-50 (closed) 2/4 TPS 800-1100 (open) 4/6 TPS 900-1200 (closed) 4/6 TPS 100-300 (open) 3/5 Safety Switch 27,000 (closed) 3/5 Safety Switch 500 (open)
Remove four screws from throttle linkage cover plate (flat plate). I broke all four of these screws when removing.
Remove four screws from diaphragm cover plate. One of the long screws is hidden – you have to remove RTV from the hole to get access to it. Search a little and you will figure out where it is. This screw also broke upon removal.
Remove throttle plate to motor linkage (pops right off).
Carefully pop off the plastic throttle body connector assembly by pressing on it or tapping using a small hammer or back of screw driver. It is snapped into the throttle body. It has some rotational play when it is installed
Remove the three (3) screws holding the motor. Use a stout screwdriver that fits the screws properly. Be careful so not to strip the screws. When the screws are reinstalled, use a little bit of thread locker.
The motor should slide out towards the connector side. Might have to tap the back side slightly to free it. Pull the connector assembly/wires/motor out of the throttle body.
Caution - take care not to damage the diaphragm during the whole rebuild process.
Drill out the broken screws. Start with a small bit centered as best you can and then work up to the screw size. Unless you are really good at this you are likely going to mess up the threads a little. I ended up getting the hole opened up to about the right size and then upon reassembly used #10 self tapping screws with correct length (available from ACE hardware). They worked well. I never replaced the broken screw on the diaphragm cover. Clean out all drill filings in the TB. This step is the hardest part of the rebuild process, in my opinion.
Re-check TPS operation per TCS Manual, rotating the motor. If you have an issue with the TPS as I had (stuck safety switch), it can be removed from the motor. You have to dig away the epoxy staking and remove the locking washers on the motor screws. The TPS then slides off the motor screws. The TPS is fully encapsulated (including the safety switch) and not repairable. By simply removing and reinstalling the TPS, I was able to clear the fault I had with the stuck safety switch. Don’t ask me how.
Clean motor thoroughly, using isopropyl alcohol or equivalent (I used WD-40 because that is all that was handy). I liberally sprayed the WD-40 while rotating the motor back and forth, wiping away any visual grease and using compressed air to blow it out and dry it. I repeated the process a few times. I did not disassemble brushes/motor but that can be done. I pressed down on the brushes with a small screwdriver to ensure they were seated well. Make sure that the little spring arms are contacting the top of the brushes.
Clean internal throttle housing/plate thoroughly. I used carburetor cleaner for this.
Verify limp mode linkage operation. Pulling vacuum on the diaphragm should release the mechanical throttle linkage.
12) Reassemble.
Observation – In my opinion, cleaning and reseating the motor brushes are probably the two best things for clearing intermittent TCS faults. I have not had one TCS hit since performing this operation. Prior to the rebuild, I was getting periodic TCS hits, especially during hot weather. One thing I did notice after reinstalling the TB was a throttle “slipping effect” that occurred when I first started driving the car. It rapidly cleared up. I attributed it to residual WD-40 that had to be dried out of the brush/motor connection.
Throttle Body Part Numbers:
9109075 – Original
4197297 – Improved TPS
9169699 – Gold plated pins (2-6), single hole in throttle lever
9170705* – Gold plated pins (2-6), two holes in throttle lever
These are the latest and best. Serial numbers above 161400 also have wedges on brushes removed for improved brush contact.
25 Sep 08
posted by 75.6.23...
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