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Pelican Technical Article:

BMW E30 Throttle Switch Replacement
Jared Fenton
Wayne R. Dempsey

Difficulty Level: 2
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

     In my continuing series of articles of the annoying E30 idle problem, I will now take you through the steps involved with replacing the throttle switch on the BMW E30 3 Series 325i models with Motronic fuel injection. Keep in mind that the vehicle in question here is my 325is, however, this article will apply to nearly every E30 model.

     Have you noticed an erratic idle that seems to stay constantly around 1500RPM then drop to 600 RPM with no known reason? Is your car constantly running lean? Well the possible culprit is the throttle switch. This small switch is directly connected to the throttle butterfly and is used to send a signal to the idle control valve, which regulates how much air is flowing into the engine to keep the engine idling correctly. The switch has only two positions, full on and full off. When the throttle butterfly is closed, it sends an electrical signal to the idle control valve to open. This allows air to flow past the throttle butterfly and hold a constant idle. When the throttle butterfly is opened past a certain point, the switch closes and the idle control valve closes, preventing extra air from entering the engine and causing a lean mixture.

     In the case of my car, I had noticed that the car wasnít running correctly, the idle seemed to have a mind of itís own. Believe me I went through everything trying to figure this out, including replacing all the vacuum hoses, coolant temp sensor (an ambient sensor that controls mixture), and the oxygen sensor. Had I known about this switch sooner, I would have saved time and money. But hey, you learn something new every day. A local BMW mechanic was good enough to point me in the right direction. Sure enough, my switch turned out to be bad. I ordered a new switch from Pelican and once installed, it cured all my idle problems.

     Hereís how you test the switch. First make sure that the battery disconnected. This is crucial. If you fail to do this, you could send a spike through the system and fry the ECU. Now open the hood, and look under the throttle body. You will see a small black box with a plug going into the side. Press and hold down the metal clip on the outside of the switch and pull it off. You will now see three terminals on the inside of the switch. These are the terminals that go to the idle control valve. What you need to do is get a hold of a multi-meter, set it to check for continuity. It will be a tight squeeze getting the terminals under the intake air boot, but it is possible. Now, check for continuity between the left outside terminal and the center terminal. While holding the test probes in place, slowly open the throttle. Just after opening, there should be no continuity. Now test the outside right terminal and the center terminal, and slowly open the throttle to the full position. As you come close to full throttle, you should see continuity return. I you fail to see any continuity return, try loosening the two screws under the switch and rotate it until you have continuity when the throttle is fully closed. If you still fail to see continuity, the switch is bad and must replaced. This was the case in my car.

     To replace the switch, we must first remove the intake air boot. This is done by first removing the upper air cleaner housing, then loosening the hose clamp that holds the air boot to the airflow sensor, which is bolted to the air cleaner. Now unplug the electrical connection to the airflow sensor by pushing the small metal bar in and pulling it off. Now, pull the air boot off the air cleaner/airflow sensor off and set it aside. Next, disconnect the electrical connection from the idle control valve and remove the rubber sleeve that holds the idle control valve to the bracket. Once the valve is loose, pull the idle control valve out of the intake boot and the connector to the throttle body. Now disconnect the breather hose from the valve cover to the throttle body. Just loosen the hose clamp holding it in place and pull it off. Next, remove the vacuum connection for the brake booster from out of the intake air boot, and disconnect the vacuum lines that connect the other end into the throttle body.

     Once all these parts have been removed, loosen the hose clamp that holds the intake air boot onto the throttle body and pull the boot off. You will now see the throttle butterfly. On the side of the throttle body, there are two coolant hoses that are used to keep the throttle body warm during cold starts. Loosen the hose clamps that hold them in place and carefully pull them off. Be aware that you will most likely see some coolant spill out of these hoses. Now disconnect the throttle and cruise control cables at the top of the throttle body. Just pull the throttle wide open and pop the grommets out, then slide the cables out.

     We are now ready to remove the throttle body. Locate the four 10mm nuts around the perimeter of the throttle body and remove them. Now pull the throttle body off, and rotate it so we can gain access to the bottom. You will see one more vacuum hose attached underneath. Remove this hose from itís fitting and set it aside. Unplug the connector for the throttle switch. Now take the throttle body to a clean work area.

     At this time, I usually like to go over the throttle body with a rag and some cleaner. This will get off all the crud and grime that have accumulated inside from years of oil mist from the valve cover breather hose. We donít have to get it perfect, but a good once over should do.

     Once clean, turn the throttle body upside down and remove the plastic cover for the throttle switch. You will see that the switch is held in place by an indexed shaft and held on by a clip on the bottom. Using a screwdriver, carefully remove the clip. This clip is under tension, so be aware that once you remove it, it will most likely go flying off, so have a rag or other means ready to catch it. Now loosen and remove the two screws on either side of the switch that hold it on and pull the switch off the shaft.

     I could immediately see what caused the switch to fail. The small soldered contacts inside seem to have broken free of the switch and broken continuity. I could just go ahead and re-solder them, however I feel that in order to solder contacts this small, you will need to have extensive experience with electronics. However, if you feel up to it, go ahead.

     Now, place the new switch on the throttle shaft in the same relative position and install the clip on the end to hold it on. Now install the two screws on either end but do not tighten them. Now grab your multi-meter and set it for continuity again. Connect the test probes between the terminals and make sure the throttle is in the fully closed position. Now, rotate the switch just until there is continuity. Now tighten the screws to hold it in place. Put the cover on and take the throttle body back to the car.

     We now have to re-install the throttle body. Remove whatís left of the old gasket between the throttle body and the throttle body and place a new gasket over the studs. Now, reconnect the vacuum hose underneath and plug the connector for the throttle switch back on. Put the throttle body in place over the studs and install four new self-locking nuts. Tighten the nuts down, but be careful not to strip them out. Once secured, re-attach the throttle and cruise control cables. Just pop them into the grommets and thread the cable in and re-adjust them to take out any slack.

     Now re-attach the coolant hoses for the throttle body. Clean off the inlet ports and slide the coolant hoses on. Once pushed on, tighten the hose clamps to hold them in place. Be sure to add a little water/coolant into the reservoir to top up any coolant that may have spilled out. Next, re-attach the breather hose from the valve cover and tighten the hose clamp.

     Once these connections have been made, place the intake air boot back over the throttle body and tighten the hose clamp that holds it in place. Now reattach the fittings for the brake booster into the air boot and also the fittings into the throttle body. You may find it helpful to put a little RTV sealant round these fittings to keep them tight inside the throttle body.

     Now re-install the idle control valve into the intake air boot while simultaneously pushing the other end into the throttle body connector. Now re-connect the electrical plug on the end of the valve. Now take the upper air cleaner and slide the intake air boot over the airflow sensor, and tighten the hose clamp that holds it in place. Lastly, re-connect the battery and start the car. You should now have a smooth stable idle that purrs like a kitten.    

     Well, there you have it - it's really not too difficult at all.  If you would like to see more technical articles like this one, please continue to support Pelican Parts with all your parts needs.  If you like what you see here, then please visit our online BMW catalog and help support the collection and creating of new and informative technical articles like this one.  Your continued support directly affects the expansion and existence of this site and technical articles like this one.  As always, if you have any questions or comments about this helpful article, please drop us a line.

Comments and Suggestions:
rotorious Comments: I have replaced the coolant temp sensor Coolant temp sensor, and cleaned the ICV on 87 325, yet when the car starts it stays at around 600 RPM and as it warms it gets up to around 1k. Once warm it will start to surge and will even surge when in gear and there is no throttle being applied. Does this sound typical of a dead TPS? thanks.
March 4, 2016
  Followup from the Pelican Staff: Sounds like the idle control valve or control module is faulty. If you block the control valve, does the idle run steady? Does TPS voltage fluctuate when the problem is present? - Nick at Pelican Parts  
blkmrln Comments: my car is an m20. I forgot to mention awhile ago. I just came upon this page again and didnt notice I had gotten a response...sorry..Fuel pressure is good new cap and rotor, msd coil. You can feel the lack of fuel in the careven though good pressure It is very inconsistent with how it runs. Sometimes it pulls good right through the rpmalways stumbles until 2k rpm. Im beyond frustrated at this point.
August 28, 2014
  Followup from the Pelican Staff: If you suspect fuel is the issue, I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
mwreyno Comments: I recently replaced my TPS using these directions thanks!. Before I was getting the up and down idle hunting pretty regularly. That's mostly been fixed but now I occasionally get a good idle around 1100 rpms but then in the morning and during driving it will drop down to 600 rpms and be really rough. Sometimes it will stabilize. It doesn't do the up and down thing that it used to but now this. Thoughts?
May 8, 2014
  Followup from the Pelican Staff: You didn't mention what vehicle you have. I would start by checking the vehicle for fault codes, then check TPS adjustment (if it is adjustable). Check the engine for vacuum leaks. - Nick at Pelican Parts  
mwreyno Comments: So I recently replaced my TPS using these directions. I was getting the up and down idle pretty regularly. It has mostly cured that although now I'm getting a low idle which sounds really rough. Around 600 rpms and some knocking. Wasn't doing this before. Sometimes will stay around the 1000rpm idle but then drops down. Thoughts?
May 8, 2014
  Followup from the Pelican Staff: You didn't mention what vehicle you have. I would start by checking the vehicle for fault codes, then check TPS adjustment (if it is adjustable). Check the engine for vacuum leaks. - Nick at Pelican Parts  
DjMossM42 Comments: Hi, I tested my TPS today and got 1.5k-4.5k ohm when testing between the bottom and center pins and the reverse between the center and top pin. I'm assuming it's bad but want to make sure.
May 5, 2014
  Followup from the Pelican Staff: Ohms don't tell me much. I test TPS sensors by backprobing while still connected. Turn the ignition ON with the engine OFF< then operate the TPS and monitor the signal voltage. - Nick at Pelican Parts  
Blkmrln Comments: I'm wondering if this is my problem. My car stumbles really bad when cold then once it warms up it only misses from idle to around 2k rpm. With my autometer a/f gauge hooked up it is very fast and sparratic back and forth from stoich to lean almost unreadable the light bounce back and forth so fast. ive replaced my fuel pump tested my air door. Any ideas
April 24, 2014
  Followup from the Pelican Staff: A/F ratio will switch up to 5 times a second on narrow band vehicles, you didn't mention what you have. I would say the data from your gauge is null.

I would check each cylinder for a misfire. CHeck spark, fuel and compression. - Nick at Pelican Parts
 
Manny Comments: when replacing the throttle switch i notice when the screws are on but not tighten, as you turn the Throttle switch box it dose a clicking sound , should i set it on that or as far from the clicking sound Switch?
April 1, 2014
  Followup from the Pelican Staff: See this step:

Now, place the new switch on the throttle shaft in the same relative position and install the clip on the end to hold it on. Now install the two screws on either end but do not tighten them. Now grab your multi-meter and set it for continuity again. Connect the test probes between the terminals and make sure the throttle is in the fully closed position. Now, rotate the switch just until there is continuity. Now tighten the screws to hold it in place. Put the cover on and take the throttle body back to the car. - Nick at Pelican Parts
 
johnbonham1980 Comments: On my 1990 325is, this took care of several idle issues at once ... before it idled at 900 when the engine was warm, 1500 when cold ... when the A/C was on, 2000+ RPM. Now very smoothly idling at 650-750 ...

Took the opportunity to degunk the throttle butterfly ... sins of the oiled air filter on the car when I bought it...

The old switch tested as having no continuity at idle, so the switch was definitely bad.

The only issue I ran into was that I ended up having to cut off the short piece of brake vacuum hose as it was really stuck on there and we could't get it to budge. Replaced with some heater hose from the local parts store ... may still need to source some stiffer stuff but so far, so good!
April 16, 2013
  Followup from the Pelican Staff: Thanks for the info. - Nick at Pelican Parts  
ecsk Comments: When I cleaned my E30 325i ICV and throttle body and tried to follow this guide to test the throttle switch, but I only found this plug under the throttle body, I'm sure it is very different from what you described. I'm in Australia, all our BMW are Euro spec, is the throttle switch in other location ?
December 7, 2012
  Followup from the Pelican Staff: A picture of the whole throttle body would have helped. A throttle switch is typically mounted at either end of the throttle shaft as the shaft actually spins the sensor. If the sensor in this picture is attached to a sensor on the end of the throttle shaft then this is the European version of the throttle switch. - Nick at Pelican Parts  
Travis Comments: I had to adjust my throttle cable in doing this procedure...any idea as to where it's supposed to be set to? or how to adjust it back to an OEM setting? I have a 1991 318i with an M42, thank you...
April 19, 2012
  Followup from the Pelican Staff: There is no OEM specific setting. Loosen the cable until you can move the pedal and the throttle will not move. Tighten the cable until the there is a small amount of pedal movement before the throttle move. Any tighter and the cable will eventually break. - Kerry at Pelican Parts  
Anne Comments: I don't know why doing this is a two-degree of difficulty, yet, and I am hoping it's rated accurately, cuz it looks as if this is exactly what is wrong with my car. My airbox had not been connected to the hanger/bracket, correctly or at all- was kind of hanging out there- til one day, it fell, when I was on the highway. That seems to have set-off a bunch of problems, especially since it was not just replacing the ambient pressure sensor and/or hoses, and doing a tune-up, etc.. Or, it was this problem and I neglected to figure it out sooner.
I hope that when I go to do this, this article will make more sense, but the names of some parts are not same as used by BMW folk, and though I can do some things with my car, some of these things just seem to not make sense, at all.
This is a great time that photos would be great. If I do this throttle thing myself, I will take photos as it goes on, and I will post them for you.
My car is an 85 319i, and is the most difficult car I've ever worked on. The others were 320's, and one Mercedes a 70 SEL with such a huge engine compartment, everything was easily accessable, and i could sit in the compartment, which I did when i replaced the alternator, myself.
To those who think it's funny that we ask for pics; we are not mechanics and auto problems and fixing them is not all that easy. It is a daunting prospect.
April 8, 2012
  Followup from the Pelican Staff: Let us know how it works out. - Nick at Pelican Parts  
Philly Comments: Thanks pelican parts, you saved me about $1000 in parts and labor. I changed all hoses liquid/vacume. Thermostate, coolant temp sensor, ICV, IC switch, all new again. When I started, my car idled at 1800rpm and 2500 with A/C on. After my overhaul, car idles at 750rpm and about 650 with A/C on. Love it!!!
April 3, 2012
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
carlospr Comments: I am trying to replace the throttle switch, but the 2 phillips screws which attach it to the throttle body are both very tight, no way to release them and head is almost damage by the screwdriver. I know it seems a silly problem but to idea how to remove them, any help??? Thks
March 31, 2012
  Followup from the Pelican Staff: You can try to put pressure on them while turning them. If that doesn't work, use a small pair of vise grips to remove them. - Nick at Pelican Parts  
Aldo Comments: I there. I have a 88' 325i with EH automatic transmission and the switch had 6 terminals inside instead normal 3 terminlas......How can I test that???
Regards,
Aldo
June 28, 2011
  Followup from the Pelican Staff: I don't have that tPS inmy wiring to checkit out. I would say the test is going to be similar. - Nick at Pelican Parts  
Stuart Comments: Hey,
I have a '84 E30 318i that needs the throttle switch replaced, and it sounds much different under the hood to the one described, any chance of some help with instructions for my particular model?
Cheers,
Stuart
August 9, 2010
  Followup from the Pelican Staff: Should be an easy replacement, the switch is located on the throttle body and is indeed similar for most E30 cars. The 318 4-cylinder is a little different, but not that much so. - Wayne at Pelican Parts  

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