I could use some help with the next steps in finding a problem with the running of my 1993 300E with the 104 2.8 HFM motor. It has had a stumble (jerk) at idle for a while now especially with the AC on, but does do it occasionally without the air, only at idle and when in gear. I recently have replaced the following items over the last 6 months.
Throttle actuator, OVP, plugs, wires, fuel pressure regulator, oxygen sensor, wiring harness in 2001, and had the head gasket replaced last week. The car has 72,000 miles on it. After the head gasket repair, the idle is beautiful, with out a bobble, but now I have drivability issues with a intake backfire at low speeds if you accelerate to quickly and a slow response to the throttle at low speeds but seems to perform better at higher RPMS. I double checked the cam timing and I believe it to be correct according to the procedure outlined by Steve B. in his article. I pulled the codes tonight and on pin 14, I get a code 10, the tn signal from the ecu and on pin 8, a code 9. What would be your suggestions on how to proceed on diagnosing what is the issue? Thank you for any help.

Bill

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87 560 SL
93 300E 2.8
91 300CE-24

Did you use Plats ????

No Arthur, I used the oem copper non-resistor plugs. I forgot to mention that I have replaced the MAS air flow sensor as well. I try to use oem parts at all times. My car does not have ASR; so does code 10 on pin 14 point to faulty rpm TN signal reading? If so, what sensor picks up this info? Thanks.

Bill

__________________
87 560 SL
93 300E 2.8
91 300CE-24

Did you change the resistor/connectors under the 3 coils ??

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Spark%20Plug%20Connector&url=http%3A//img.eautopartscatalog.com/live/F101084561BER.JPG

The are notorius for your condition.

Yes, I have replaced the connectors. With the intake backfire that happens, does this point to a lean fuel condition? Other than the fuel pressure regulator, I have not gotten into the fuel system; I did check the purge valve and clean it. I have checked for vacuum leaks as well. The car seems to run well until operating temps achieve closed loop operation and then all of the symptoms start. We drive the car every day and I really would like to get everything ironed out. I am thinking about buying 1 fuel injector for diagnosing them one at a time. I feel like I am running out of options.
Thanks,

Bill

__________________
87 560 SL
93 300E 2.8
91 300CE-24

Those are very long lasting, and expensive, injectors. You can get them rebuilt and fully tested for less than the cost of buying one. Your car will be down for a few days however.

www.cruzinperformance.com

Thank you for the advise and web link. This looks like something I may take them up on. I have some downtime coming up where I can spare the car being down for the week.

Bill

__________________
87 560 SL
93 300E 2.8
91 300CE-24

B/C you just had the head gasket done, I would check the air intake cross-over pipe clamp at the throttle end has been tightened . This is an often easy over-sight when putting the car back together..it requires a long screwdriver or extension from the front. If that clamp is not tight, you are getting unmetered air and a lean condition, most noticible at lower partial load .
While you are there , make sure the little Air Intake Temp sensor has been plugged back into the same cross-over pipe..[ 1/2 way between the MAF and the throttle end]
That could also be the 02 sensor code.

Thanks Arthur, I will check both items first thing tomorrow. I hope that it is one of these. Do you have an idea what can cause the tn rpm signal code and what that means?

Bill

__________________
87 560 SL
93 300E 2.8
91 300CE-24

TN sig is engine rpm sig at N3/4 ECU.
That code will pop if CTP sw is not closed or hanging up ..Check the slack on the cable [ sholud have just a little] , Clear code.
If it comes back , you ae looking for 5-12v at pins 34 and 37 at ECU with Throttle closed , key ON.
I doubt you will se that again after clearing.. it can come up if one lifts the throttle by hand under hood when working on car.