Hello to all. I recently purchased a '94 E420 with 60,xxx miles. The first month was great, and then trouble started.

I started the engine one morning and it hiccupped, ran very roughly, and then stalled out. I cranked it again and it started but stalled out again. On the third try it started and ran pretty much as normal. That afternoon the check engine light came on and it was having almost stalling episodes when first started. I took the car out to the MB dealership and they coded it to the MAF Sensor. I cursed a good bit but bit the bullet and bought a new unit and had it installed. When I picked up the car the service advisor said that there was a "soft code" for the TBA that wouldn't clear.

Sure enough that afternoon the check engine light was back on and the car was displaying the same symptoms. I should note that the cruise control also quit working with the second check engine episode. Anyway, the car would start and then the RPM's would dip super low and sometimes stall out. We bought a rebuilt TBA unit from Beckmann Technologies in NC (great service) and installed it, but did not have it immediately recoded at the dealership. Here is what it did. Upon start-up, the car idled about 500 to 700 rpm higher than it did previously, and when put in park the idle would cycle up and down about 300 rpm. When driving the car runs flawlessly but sometimes when letting off the gas you can feel the cycling for a couple of times and then it will settle down. The cruise still doesn't work. We took it out to the dealership to have the TBA coded, and they couldn't get the TBA trouble code to clear. They said to me that the rebuilt unit had to be bad.

I called Beckmann and they sent out a replacement unit with the warning that if the original replacement tested good that I would have to pay for the second rebuilt unit. You can probably see where this is going. We installed the second TBA this morning, went straight to the dealer to have it coded, only to have the same problem happen again. So it seems as if I will have spent close to two grand on parts by the end of this week with the car having the exact same problems as before.

Can anyone on this forum offer any advice as to what else could be causing such problems. The wiring harness has been replaced so I don't think that it is a factor in this case. We have an appointment with an independent mechanic on Monday who thinks they may be able to better diagnose the problem, but I do not have unlimited funds to try to solve a problem that should have been solved by what the dealer told me needed replacing.

Thank all of you for your knowledge and any insight you can give me or the mechanic who will be looking at it on Monday.

Sounds rough. Look on the bright side - you now have enough spare parts to last for many years to come. The dealer is not taking responsibility because you're not buying the parts there. In fact you have no one taking responsibility. If I were in your shoes I would learn how to read the fault codes (by doing a search above) and then read and clear them every day until a clear trend developed. That sort of behavior should put off some fault codes. BTW, that sounds like a bad policy by Beckman - I would hope they would reconsider, might be worth a try.

Did you try running the car in second gear to see if it runs better than in 1'st?

I have seen the neutral safety's on the side of the trans do strange things like that.

Sometimes they get a hot spot in the drive position of the switch because it is always there, and if you put it in second it may run better, but if it went into limp home mode, it won't matter what gear you are in in most cases.

Also ,it won't hurt to ask the independent guy that if he does not fix it, he does not charge you right?

Fortunately the service advisor at the dealership is a somewhat friend of the family so they haven't charged us for any diagnostic work they have done so far. The problem is that the trouble code for the TBA being bad won't clear, at least that's what I got out of the conversation. The tech that my dad spoke with is now interested in the solution to the problem so if we get no further with any suggestions this weekend or on Monday, we will go back to the tech at the dealership next week.

It's not as if there is any roughneess in driving or in the transmission, it's just that when you let off the gas you can feel the engine trying to surge a couple of times while it is dropping rpm's.

On a cold start the engine will idle at 500 to 600 rpm, as if there is no problem, but as it starts to warm the idle increases to the 900 to 1200 rpm range.

Does anyone know if these are any symptoms of a bad module?

Thanks for your suggestions so far.

I Had The Same Trouble With A 1992 400e. Spent A Small Fortune On It As It Would Not Store Fault Codes. Finally It Was Determined (guess) That It Was The Throttle Body Causing The Problem. I Seem To Remember That Once The Tb Has Been Replaced, The Engine Mgmt System Must Learn To Communicate With It Properly. You Cannot Just Start The Car And Drive It. There Is Some Simple Procedure One Has To Do (mechanic) To Initiate This Relearn. Then All Should Work Correctly.

The Only Other Thing I Can Think Of Is Vacuum Leaks Somewhere (maybe The Gasket At Bottom Of Tb). Good Luck.

JUST REMEMBERED ANOTHER TWO FACTORS ---- BRAKE PEDAL SENSOR & GAS PEDAL SENSOR OFTEN CAUSE PROBLEMS ALONG WITH TB MALFUNCTIONS.

I hope this would help, read my post...

1994 MB E420 issues idle/surging/stalling LONG

Hi to all and thanks for your suggestions. I took the car in to an independent shop where they eliminated all the other variables that would cause a fault for the check engine light to come on. They diagnosed it as a faulty idle control/cruise control module (part #124 545 36 32). Seems these modules are getting hard to find on the used market but we were finally able to track one down. Many thanks to Pat at Potomac German Auto for his help!

This just goes to show that trouble codes or fault codes don't always point to the root cause of the problem and it is getting hard to find skilled mechanics who can use a wealth of on the job experience to diagnose a problem and work on a car approaching 12 years old.