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HomeTech Articles > Calibrating the 914 Throttle Positon Switch

Guest Technical Article:

Calibrating the 914
Throttle Position Switch

Mike Cooley
mikecool@netten.net

Mike Cooley has donated the procedure for calibrating the throttle position switch in your 914.

The procedure for calibrating the throttle position switch on the 1.7 and 1.8L cars can be found by clicking here.

The procedure for calibrating the throttle position switch on the 2.0L cars can be found by clicking here.

Comments and Suggestions:
socal1200r Comments: On the link for calibrating the TPS, I have to ask an obvious question. It says to zero the ohm meter, attach the leads to specific pins on the switch, etc. Since the instructions don't mention it specifically, I'm assuming this is done WITHOUT the harness connected, and the engine off? If so, how is it supposed to read anything if there isn't any power going to it? Just asking the question!
September 14, 2016
  Followup from the Pelican Staff: To zero your meter, touch the lead to each other and push whatever button zeros it, will be specific to your DVOM. - Nick at Pelican Parts  
socal1200r Comments: "Look for a vacuum leak first. The intake plenum is usually the culprit." I'll check the four boots that connect the plenum to the intake runners; where the TB bolts to the plenum; and any hoses around those areas.

Not sure if this is part of the problem, but I did remove the stock airbox and installed a small cone filter. I used a 2.5" - 3" silicone coupler at the TB inlet, into a 60-degree hard elbow, then attached a small cone filter at the end. There were three hoses that attached to the airbox. The long one I left as is, and attached a breather filter on the end. The other two I followed down to the source, removed the hoses, and stuck a breather filter on top of the outlets. Didn't make the car run any worse, and I can hear the TB sucking in air, where before I couldn't. So I don't think those changes are at fault, because it was running bad before I added those filters.
September 13, 2016
  Followup from the Pelican Staff: I would put it back to stock to see. Usually these modification cause issue. - Nick at Pelican Parts  
socal1200r Comments: "Mechanical timing has to be checked by lining the engine up in TDC and confirming the camshafts, crankshaft and timing marks lining up." Yikes, that's WAY beyond my limited skills. Guess I'll try and eliminate the simple stuff first, before heading to the more complex like this...
September 13, 2016
  Followup from the Pelican Staff: Look for a vacuum leak first. The intake plenum is usually the culprit. - Nick at Pelican Parts  
socal1200r Comments: If it's "mechanical engine timing", does that mean it can be checked the old-school way, with an inductive timing light and timing marks? If so, I'm assuming you clip to cylinder #1 to read it? Where are the timing marks, and what should it be set to? Not sure how to check for vacuum leaks though, except to check the hoses for connections or tears.
September 13, 2016
  Followup from the Pelican Staff: Mechanical timing has to be checked by lining the engine up in TDC and confirming the camshafts, crankshaft and timing marks lining up. - Nick at Pelican Parts  
socal1200r Comments: I just picked up a low miles 77K 1973 914 1.7L. Everything seems to work fine, except for acceleration. The car bucks and surges when below 2500 rpms, and doesn't seem to accelerate like it should when you push down the pedal altho the bucking and surging smoothes out. I'd like to keep the FI system, so I'm doing online research to help cure this problem. Question - where is this switch located? Is it on the throttle body itself? I have one of those multi-meter gizmos, so I should be able to use one of the settings on that meter for this tech tip? Thanks
September 12, 2016
  Followup from the Pelican Staff: The switch is on the throttle housing. Your issue sounds like a large vacuum leak or mechanical engine timing. - Nick at Pelican Parts  
mike I Comments: One bit of oddness I experienced on my '74 2.0

I replaced the throttle position circuit board. Put the TB back on car, hooked up some jumpers and could not get a reading other than 1.

Figuring I might have the jumpers wrong I removed the TB. Jumpers were correct and I was able to calibrate on the bench. Left the jumpers in place, put the TB back on car. Checked reading, still zero.

I now hook the linkage back up and notice the reading is back at 1. Loosen the screws, go to adjust and same as before, only shows 1.

Seems to be OK with bench calibration but not sure why I can't seem to calibrate on the car?
June 30, 2014
  Followup from the Pelican Staff: On the car, is the wiring connected? There may be a short preventing the adjustment. - Nick at Pelican Parts  
luke Comments: yeah Ok so where are pin 12 and 17 on the 4 contact TPS?
January 4, 2014
  Followup from the Pelican Staff: Check here for a wiring diagram for your vehicle:

http://www.pelicanparts.com/914/914_electrical_diagrams.htm - Nick at Pelican Parts
 
luke Comments: have you noticed that the TPS you show has 5 contacts? the TPS out of my 1971 914, 1.7 only has 4 contacs
January 4, 2014
  Followup from the Pelican Staff: There may be variations from year to year. - Nick at Pelican Parts  
Mike Comments: I rotated the switch as in point 4 CW. In point 5 it says to rotate the switch CW even more but it can't be done as it reaches a stop point. What "one more hash mark" means?
June 8, 2013
  Followup from the Pelican Staff: The hash marks are on the slotted adjustment bracket. You will see small marks on the (retaining) adjustment brackets.- Nick at Pelican Parts  
johnson Comments: 1974 should be Djet engine i have replaced the circuit board for the throttle position switch calibrated and check with a meter and it read from 0 to different reading ramdom not smoovely just above idle spudders skips badly 2.0 engine have any idear.
February 21, 2012
  Followup from the Pelican Staff: If the reading is not steady, you could have one of four issues, the supply voltage, the ground, the wiring or the board. I would start by testing the wiring and the voltage into the switch.- Nick at Pelican Parts  
raul Comments: how i identify a 2.0 throttle from the 1.7?
September 22, 2010
  Followup from the Pelican Staff: This is the engine size of your vehicle. What vehicle do you have? - Nick at Pelican Parts  
GErry Comments: The throttle position switch in "NLA".
What are options to get rid of the stumbling at 3,000 RPM?
August 11, 2010
  Followup from the Pelican Staff: You can open up your switch and carefully clean the contacts with some electrical contact cleaner. This should fix the problem with the switch, if indeed that is causing the 3000 rpm problem. - Wayne at Pelican Parts  
JB Comments: Hi Mike, thanks for the article. I was wondering if you could maybe add a section on accessing the TPS, I think it may be oriented in different positions on the throttle body depending on year.

Thanks,
JB
September 5, 2009
  Followup from the Pelican Staff: The Throttle Position Switch (TPS) is black plastic and is always attached to the rotational shaft of the throttle body. - Wayne at Pelican Parts  

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