throttle position switch or sensor problem
 

Ok so this is the part that I have been getting the error code on my 96 300D. It is setting off the check engine light, with the display that reads check engine electronics. The car has a good deal of hesitation around 2000 - 2500 rpm until the engine is at operating temp of 80 degrees. So, has anyone had any issues or know anything about this?

if you have the error code number, it might help determine what the problem is. I have the same year car and model, and at first glance, I would say it might be a glow plug issue, but if your glow plug dash light is operating correctly that should eliminate that problem. The other area you might consider depending on the error code is the resonance crossover switch. That switch is dormant until you get to the rpm range you mention, at which time the crossover switch goes into it's first mode of operation. If the switch is not operating properly, your resonator flaps will not engage as designed, and may cause rough running at lower engine operating temperatures. Good luck....

the below code information was kindly provided by another poster. After changing out the glow plugs in my 96 e300d, and after putting everything back together, I ended up with an error code of P0200. Upon further investigation, I found that during the process of changing the glow plugs, I must have broken one of the wires that control the switchover valve on the underside of the intake manifold, which caused the code to come up. Repaired the wire, and all was well:





The generic reader code P0200 can come up as a result of the following MB specific codes from stealership or a good independant MB shop:
P1220=Fuel quantity actuator (IFI) (Y23/1)
P1223=Fuel rack position sensor (Y23/1l1)
P1475=Resonance intake line switchover valve (Y22/7)
P1476=Resonance intake manifold switchover valve (Y22/6)
P1611=IFI control module (N3/7)
P1613=IFI control module (N3/7)
P1614=IFI control mudule (N3/7) or fuel metering actuator (Y23/1k1) or fuel rack position sensor (Y23/1l1)
P1617=control module not coded
P1622=Electohydraulic shut-off actuator (Y1/1)

I have a similar 'hesitation' problem with my '96 but at parking lot speeds only and not all the time. I suspect the throttle position sensor and am trying to ignore the problem until it gets worse. I'd like to open up the TPS, clean it, and have the problem go away but don't know if that is possible. The TPS looks to be just a big (expensive!) potentiometer.

Jeremy

Biglex - Have you cleaned the resonance and EGR flaps recently? With cold weather arriving they may be gummed up enough that they are now sticking until things get good and hot.

Nope, and I wouldnt know where to begin. Any DIY info about doing this?

I'd be interested in a photo DIY also but in the meantime...

As I understand it, there are two flaps in the air intake circuit, one near the EGR valve and another in the intake manifold (underneath, where it's hard to see, much less touch). These flaps get gunked up with exhaust that the EGR valve lets in when the engine is cold. Eventually they gunk up to where they stop working properly. The purpose of the flaps is to "tune" the intake pipe so that it resonates properly for any given engine speed -- it's similar to tuning a speaker system with ducted ports and such. The tuning is one of the reasons why the 606 NA engine makes almost as many ponies as the older 603 turbo engine.

All you have to do is to take the intake plumbing apart, clean all of the gunk off of the inside (including the flaps) and put it back together.

It should also be possible to temporarily defeat the function of the EGR valve for testing purposes only by putting a piece of sheet metal at the place where the EGR valve mounts onto the intake ducting. The electronic and vacuum components will continue to function normally so the computers won't throw any codes but the dirty exhaust gases will be kept out of the intake. Once you have confirmed that the intake is now staying clean, you can restore the EGR valve to functionality by removing the block.

I intend to try this myself but have not yet so I cannot vouch for its effectiveness. Others have disconnected and plugged the port in the exhaust system and connected the EGR valve to a small filter. Thus, air is still allowed into the intake but it is now clean air instead of dirty exhaust. Note that this latter trick may not work on the later turbocharged engines.

Jeremy

#8 occurs in two locations. The IM and flap housings get gummed up with crud and can get sticky.

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=210020&M=606%2E912&GA=722%2E438722%2E600&GM=717%2E446&CT=M&cat=19T&SID=14&SGR=030 &SGN=02

Would be most useful to know what code is present.

I just checked iwth the mechanic today, he said he didnt remember right off the top of his head what the code # was, but that it actually read "throttle position sensor" or "throttle position switch".

Ok, just a touch of an update. still having the problem since the part is $491, but I am wondering about the smoke. While the car does this little bit of hesitation that it does, I can see alot of gray to white smoke out the exhaust. So my question is what is the smoke meaning, what is black smoke as opposed to white?

just an update, after fooling around with this, i noticed that the mechanic had left a small hose from the TPS running to the intake manifold off. it was just laying right beside the intake. I put it on, the hesitations stopped, and the MIL cleared itself. Not sure what the hose is, but it was certainly the culprit. Saved me $491.

What is this hose? Can you post a picture? I don't have any hoses on my TPS, just a couple leading to/from the transmission vacuum controller plus a loose (black) hose that I'd like to find a home for -- it's possibly a vent but I can't find any information on it.

Jeremy

96E300d here, and I had a code P0120 come up, which seems to be a generic code for a TPS malfunction, but does not mean that the TPS sensor itself is the culprit. After doing some searches, another poster brought up the fact that the TPS is also in a circuit with two other vacuum pressure sensors located on the side of the air filter box. One sensor controls the egr valve, the other the resonance flaps. Also in this vacuum circuit, is that small hose that comes off the intake manifold. It seems that all three work in conjunction with one another along with the TPS, and send information to the computer system. In my case, I cleaned off the vacuum pressure sensor that controlled the resonance flap circuit, and the code dissapeared.