TPS question - Adjustment - PeachParts Mercedes-Benz Forum

meltedpanda · #1 11-04-2012, 05:16 PM

I think I may have found Pearls idle issue - I think the TPS was out of adjustment or that is my thought and reason for the post

at full stop ( with .04 spacer ) should the pins 12 and 17 not have continuity ?

at full stop with out feeler guage - should I have continuity ? Is that stop 1 of the 10??
Then just past that continuity and then 9 more stops - total 10?
12 and 17 are the correct pins for this test??

When i took it off I was just getting 9 , now I have 10
I had to adjust stop and the TPS to make it happen. What should the throttle plate look like at full stop - totally closed I assume?
before I put it back together - thought I'd ask

I wonder if the rich running I have been having could have to do with this, I think it was sitting on or just past first continuity stop???

thoughts oh great minds??

Graham · #2 11-05-2012, 10:43 AM

Quote:

Originally Posted by meltedpanda

I think I may have found Pearls idle issue - I think the TPS was out of adjustment or that is my thought and reason for the post

at full stop ( with .04 spacer ) should the pins 12 and 17 not have continuity ?

at full stop with out feeler guage - should I have continuity ? Is that stop 1 of the 10??
Then just past that continuity and then 9 more stops - total 10?
12 and 17 are the correct pins for this test??

When i took it off I was just getting 9 , now I have 10
I had to adjust stop and the TPS to make it happen. What should the throttle plate look like at full stop - totally closed I assume?
before I put it back together - thought I'd ask

I wonder if the rich running I have been having could have to do with this, I think it was sitting on or just past first continuity stop???

thoughts oh great minds??

Throttle plate is fully closed, but is still at slight angle to horizontal.

This is from the pdf I did a while back:

Quote:

The shop manual shows which pins to use to check the switch. 12 & 17 test the idle switch. The resistance between these pins should be zero when the throttle is against it’s stop. If the throttle is slightly opened (1 degree or 0.4mm feeler under stop), the resistance should go to infinity. This switch tells the ECU that you are idling.

If the idle switch is not actuating, your idle mixture would be controlled by the MPS/ECU mixture control instead of the ECU idle control circuitry (adjusted by knob on ECU).

The TPS probably won't affect mixture other than at idle.

meltedpanda · #3 11-05-2012, 04:53 PM

yes , thanks, after I posted I found that article in the stack of papers I had. Yes the idle is my issue, so I hope I have found the cause. I checked everthing else to check, no vacuum leaks, trigger points are new, sensors are all new..
wish me luck

meltedpanda · #4 11-06-2012, 08:47 PM

does the small ( tiny ) vacuum hole on the back of the intake, sit above or below the throttle plate when the plate is fully closed?

Anyone care to check their 450?

RadioTek · #5 11-06-2012, 11:00 PM

If I remember correctly, there is a set of TPS contacts that are closed to tell the computer that the throttle is at idle. When the plate is closing off the intake, the idle air is supplied to the manifold through the Idle valve from the large hole in the throttle body. So the fuel mixture is controlled by the knob on the "computer".

When the "throttle closed" contacts are opened as the plate opens, the fuel/air mixture is controlled by the sensors with the MPS. If I remember the theory of the D-Jet system correctly.

So you need to have the TPS correctly adjusted by the procedure in the manual. The plate in the specified position, then the "throttle closed" contacts of the TPS closed.

Be careful, that bottom adjusting screw is hard to get to.
Scott

meltedpanda · #6 11-07-2012, 10:34 AM

thanks, I have the TPS adjusted as you mention and now just want to make sure the small ( tiny ) air port on the back of the throttle body should be above the throttle plate when the plate is fully closed ( against stop)
Not sure if this is minor or not, but just want to make sure. It sure looks like it is designed to be above

Graham · #7 11-07-2012, 05:21 PM

Ron,
That small hole leads to a tube that eventually connects to the distributor via a switch over valve. It's function is to provide vacuum to the distributor diaphragm which retards the timing when the engine is at idle.

I order for it to provide a vacuum, the hole has to be below the throttle plate. It should automatically be when the throttle plate is fully closed.As soon as the throttle plate moves, you start to lose vacuum and the timing gets more advanced. This is covered in section 14 of manual, although it is not that clear.

Those little holes are often plugged up. They don't go straight through - I think I pushed a small flexible wire through until the hole was clean. Good idea to clean and at same time make sure the tubing is intact and connected to at each end and to the switch over valve.

BTW - Later (75?) D-Jets had two or maybe three such holes - one above and one below plate. To do with emission controls, I believe.

I borrowed this pic from another site. Our early 107s have just the vac retard port:

cushjbc · #8 11-07-2012, 06:02 PM

MP & Graham,

I am in this rowboat - about 5000 miles away from my car right now; will gladly check this weekend. My mental picture leads me to believe that Ron is asking about the vacuum port that is connected to the switchover valve on the right fender. I will look for pictures

meltedpanda · #9 11-07-2012, 07:38 PM

correct Brad and if I follow Graham that hole ( one on my throttle body) should be below my throttle plate when fully closed, mine is not , I will need to adjust and then readjust TPS. All other connections present and accounted for and in good shape

rowdie · #10 11-08-2012, 07:26 AM

Ron. Pulled my spare ('72) off the shelf to check. Graham's picture is exactly where mine was adjusted. Plate blocking hole. Tried adjusting so the hole is below the plate but the plate will start sticking if you go too far. Good luck.

meltedpanda · #11 11-08-2012, 01:18 PM

thanks Rowdie, I am beginning to think my on off idle issues and rich running at idle are all related to the TPS and throttle plate. SOon I will know, just have to carve out time to get this thing back together

meltedpanda · #12 11-10-2012, 06:48 PM

I had time to mess with her today , got everything spot on , throttle plate, TPS tuned, check all lines, checked all sensors, adjusted linkages per manual. Put her back together and she purrs like a kitten.
I really think I have had a rich running erratic idle for some time. I believe the last time I put her back together I screwed something up, and when the weather turned colder , the issue surfaced more noticeably.

that or I'm just crazy , which lately that is a real possibility

In any respect, thanks for the input

Graham · #13 11-17-2012, 10:01 AM

Quote:

Originally Posted by rowdie

Ron. Pulled my spare ('72) off the shelf to check. Graham's picture is exactly where mine was adjusted. Plate blocking hole. Tried adjusting so the hole is below the plate but the plate will start sticking if you go too far. Good luck.

Over the past couple of days, I installed new hoses on my injectors. While in there, had a look at the throttle plate. The way it is made, it automatically closes with the hole below the plate. If it isn't it must be that stop is preventing it from fully closing.

Regarding the hoses - I had previously used 5/16" (7.9mm)J30R9 SAE hose with the blue liner. I had many leaks with that hose. Had to keep tightening the clamps. Perhaps the blue plastic (fluorocarbon/nitrile) liner "flows"? I bought the new 7.5mm hose from MB dealer. (part 230-476-87-26). No leaks after 1 day

meltedpanda · #14 11-17-2012, 09:25 PM

yup , I ended up using the MB only stuff, no issues since. BTW - idle is still perfect!