How do you check/adjust Throttle Position Sensor???

[david914]

OK, OK. I did a search and didn't come up with a definitive answer to my question. I've checked my Haynes manual and it's no help (I know, time for a Bentley manual). Problem is my '86 has a slight "bucking" problem on acceleration, particularly when cold. Started checking a few things, including the DME relay. Took the time to remove the DME relay and re-flow all the solder joints that looked suspect. No luck there. Checked the connections in the engine compartment (O2 sensor, etc.). Everything looks good, but one contact on the speed sensor, but I'm pretty sure it's still making contact. Move on to the TPS. Checking resistance between the upper and middle contacts (the two that are actually connected to the harness when plugged in), I get infinite resistance at idle, then I get 0 ohms at about 3/4 throttle. Is this correct and if not, how do I adjust it?

[ChrisBennet]

The '86 doesn't have a throttle position sensor in the usual sense. What looks like a TPS on the side of the throttle body is just a Wide Open Throttle Switch. The WOT switch shouldn't come into play unless you are at full thottle.
-Chris

[david914]

So, it sounds like mine needs to be adjusted or replaced? It doesn't appear to have that much adjustment left in it, unless of course a little goes a long way at the TPS end of things. Right now the TPS goes to 0 ohms at about 3/4 throttle. Proper setting is not to hit 0 ohms unless the throttle is all the way open? Do you think this could be causing the slight "bucking" and lack of power at part throttle that I'm experiencing?

[Purrybonker]

I'm pretty sure WOT switch should kick in at about 3/4 throttle. Once the switch is open voltage falls from 5 to 0 signalling the DME to go to WOT map and ignore other sensor inputs (eg O2 sensor).

I doubt WOT switch is the cause of your problem.

[david914]

Hmmm. Well, sounds like I should start looking at other things that might be causing my problem. I'm pretty confident that the engine temp sensor isn't the cause as it was replaced by the PO recently. I guess the next items to check would be the intake manifold bolts and gaskets, and the 02 sensor (I don't see in the receipts that it has ever been replaced). Anything else that you guys can think of that I should look at?

[Dan Owens]

I'd toward O2 sensor and adjusting the AFM. Has the sensor ever been replaced? Does it run okay when your heavy on the gas but buck under light acceleration? Have a flat spot at about 3500 RPM's or so when you'r light on gas?

[david914]

Exactly Dan! It reminds me of my Weber carbed 914 before I got the jetting right. It bucks under light acceleration and doesn't seem to have the low to mid band power that my SC does. Full throttle seems fine.

[Dan Owens]

David,

Here's my symptoms the last two times I've needed a new O2 sensor. Bucking under light throttle at about 3000 RPM while trying to maintain low speed, especially while cold. Flat spot at about 3500 RPM to 4200 RPM under light throttle, hot or cold, felt like lack of gas. Past that point normal feeling, under heavy throttle almost no flat spot, no bucking. I've had the AFM reset after replacing the O2 sensor.

If you haven't replaced your O2 sensor in the last 40K miles then you should consider that needs to be done regardless. It may also need to have the air fuel mixture checked and adjusted. Your symptoms are common for for those two issues but not exclusive to them.

The Cylinder Head Temp sensor can give the same "bucking issue" if I'm not mistaken. Bad wires, old cap and rotor may also be contributing to the problem too.

If I were a betting person and you haven't had the O2 sensor replaced then that's what I'd be looking at. I'd have the AFM checked for adjustment.

[david914]

From what you've described, my money's on an 02 sensor. The head temp sensor was recently replaced (by the PO. I've got the receipt), along with the plug wires, cap, rotor, plugs, yada-yada-yada... The car's got about 70K miles on it and no evidence of the 02 sensor ever being replaced. Sounds like it's due...

[john walker's workshop]

i had one like that a couple of weeks ago. i attached my test airflow meter, and it smoothed right out. night and day.

[Dan Owens]

Well if John's chiming in here about the air flow meter I'd listen. Your O2 sensor is old, as I mentioned in my experience each time I've adjusted the airflow meter along with the sensor replacement so could be either or both in combination. air flow meter adjustment is cheap and easy.

[david914]

Yeah, I think replacing the O2 sensor would be a good start. By adjusting the airflow meter, are you referring to the air bypass adjustment? I've got a Bentley manual on the way from our host. Does it have the procedure for the adjustment?

[CrossT]

There is an easy way to 'renew' the contacts in the AFM by resetting the position of the sweeper arm inside to run a new track on its contacts. It's worth a try - can't lose anything there. You can find that via search in this BBS. There is a 944 refurb procedure described here

http://frwilk.com/944dme/

todd
86 coupe

[Purrybonker]

Originally posted by john walker's workshop
i had one like that a couple of weeks ago. i attached my test airflow meter, and it smoothed right out. night and day.

I assume that you mean that you swapped out the AFM for a known good box? In other words the existing meter had "issues". Comments keep coming up here about "adjusting the AFM" - there is no ability to adjust mixture on Carerras - so I guess the reference must refer to some type of mechanical overhaul of the air flow meter?

[john walker's workshop]

a known good unit, yes. the mixture can be adjusted by turning the 3mm allen screw in the box. the O2 sensor is disconnected when you do this. however, upon reconnecting it, the O2 sensor system pretty much adjusts it where it wants. an initial setting of 1 to 1.7% does seem to help get a smoother idle and cold run period.

[david914]

Todd,

Thanks for the link! I'll give that a try if the AFM tests bad.

John,

Sounds like I should replace the O2 sensor, then find someone who can set my mixture for me. Thanks for the tips!

I know this may open up a whole other can of worms, but... What are your thoughts on using a generic Bosch O2 sensor vs. the Porsche part? I helped a friend put a generic one in his '84 and it seems to be OK.

[Vincent Hill]

Originally Posted by john walker's workshop

a known good unit, yes. the mixture can be adjusted by turning the 3mm allen screw in the box. the O2 sensor is disconnected when you do this. however, upon reconnecting it, the O2 sensor system pretty much adjusts it where it wants. an initial setting of 1 to 1.7% does seem to help get a smoother idle and cold run period.

Mr. Walker! I am still happy with the canyon Cylinder Studs👍🏾👍🏾

My Question is, my Throttle Position Sensor on the Right side of the Throttle Body is loose. The plate holding it is loose and looks like the Right front screw that holds the plate is missing but the Sensor is in the way of putting in a new screw. Any suggestions? Can the sensor be pried apart. I tried using a Dremel to remove a little of the Housing, but did not want to go too far!

[Vincent Hill]

Originally Posted by Vincent Hill

Mr. Walker! I am still happy with the canyon Cylinder Studs👍🏾👍🏾

My Question is, my Throttle Position Sensor on the Right side of the Throttle Body is loose. The plate holding it is loose and looks like the Right front screw that holds the plate is missing but the Sensor is in the way of putting in a new screw. Any suggestions? Can the sensor be pried apart. I tried using a Dremel to remove a little of the Housing, but did not want to go too far!

After thinking about this for a While, I used a side Ratchet Short Flat blade Screwdriver and “Un Screwed” the screw as far out as I could. Then squeezed Blue Loctite around the Screw and the space between the plate and Throttle body. Then Tightened the screw as tight as I could get it! Yes this is only “1” of the screws but if it holds, the Sensor will not move or move a lot less. And if I Ever drop the Engine or have to remove the Throttle body, then ALL of the screws will get the same treatment 👍🏾👍🏾

[mikesarge]

Originally Posted by david914

Todd,

Thanks for the link! I'll give that a try if the AFM tests bad.

John,

Sounds like I should replace the O2 sensor, then find someone who can set my mixture for me. Thanks for the tips!

I know this may open up a whole other can of worms, but... What are your thoughts on using a generic Bosch O2 sensor vs. the Porsche part? I helped a friend put a generic one in his '84 and it seems to be OK.

I think I’d start by disconnecting the oxygen sensor and driving it. Still bucking? Starts to seem more like AFM. If the bucking stops, then I’d swap oxygen sensor.