jljimenez

Sorry, I am Spanish and my english is not as fluent as a I would like. I have an Automatic W124, 103.940 Engine, high milleage, when cold when I press the accelerator the engine goes up R.P.M. right but when hot it hesitates between idle and 3.000 R.P.M.

May somebody help me?

bamberger_1

Hi,
as a remote diagnosis is always problematic, I would propose the the following tests:
First check all ingnition cables for good contacts in the plugs both ends. Check the spark plugs. Also the following check may be appropriate: let the engine idle at nominal temp. and pull one by one ingnition cable and see if the idle changes. In case you pull one and the idle stays unchanges it could be the cable is defect, because the engine running on 5 cyl. only should definitely roughen the idle further.

Get yourselve a can of what's known as "start pilot" (brand name) to cold start small engines like lawn mowers or mopeds. It is a spray can containing in principal high grade alcohol (dont drink it:-)) which is sprayed into the air-intake to enrich the air/gas mixture to start the engines.
You can also use "brake clean" spray.
What you do is take off the air filter and than let the engine idle at say 80 degrees engine temp. (check gauge in the dashboard)
then you spray every injection valve area individually, then you spray the intake manifolds, then you spray the rubber hoses around the manifold with the alcohol spray. In case the idle speed increases in one of the areas sprayed there is an air inflow which normally increases the air content of the mixture in the cylinders, which may cause the rough idle.
If you spray directly into the air intake (where the air filter sat before you removed it) you can check the reaction of the engine when the mixture is enriched with extra fuel.

I had this once and I had to reseal the injector seats, with new rubber seals. If you are a DIY it can be done. However the danger is to ruin the threads when putting the injectors and the holders back in place. When done carefully and patient its a cheap fix, since the seals are only a few €. (my guess € 10.- may)

Another problem could be the cold start valve leaking extra fuel into the cylinders causing rough idle too, since the mixture is enriched with extra fuel not required when engine is hot. This is hard to test, because the fuel pressures have to be checked. In case the first test does not work out than you might have to have the fuel pressures checked at a workshop anyway.

richp

How long has it been since a tuneup? Many times, on these cars, its the simple things that are the problem.

I've found that if I go too long past a scheduled tune up that my 300E will do this. Check the plugs for fouling and the cap and rotor for electrical arcs and replace if there is any sign of problems.

jljimenez

Thanks Richp, I have just -about 200 milles ago- replaced cables, plugs, rotor and distributor and the problem continue. This weekend I will try with "bamberger_1" advertisements about an extra air inflow, yesterday I got a product like "start pilot".

I will keep you informed.

Thanks to you and to "bamberger_1"

jljimenez

Hi,

I have got a clue from some people in Germany and Bamberger_1 translated it for me. Thanks Bamberger_1.

It was about the air-flow meter potentiometer, in fact this weekend I dismantled this piece –black plastic cover with four screws- that is attached at the Air-Flow Meter body and reads the position of the disk. The carbon lines of this potentiometers were worn in a zone –may be between the position where the disk is located when the engine is between idle and 3.000 RPM-. I cleaned this carbon lines, I gave more pressure to the brushes that run over this carbon lines and fit this element again. The engine now goes a little better but still hesitates –only when hot and between idle and 3.000 RPM, more or less-.
Now I think that the gasoline/air mixture is too poor because with the air filter removed, when I accelerate if I push with my finger the disk of the Air Flow Meter the engines goes up RPMs right, may be the reason that the engine runs better when cold is because the mixture is richer or may be that when I push, I put the disk at a location where the potentiometer reads right.

The reference that have printed the potentiometer is 3 437 224 015.

Please, if anybody knows how to get this piece, tell me.
Sorry about my English, I know it is not fluent.

Best regards,

bamberger_1

Question: if the car is in idle mode you push the disk of the air intake and than the rpm go up? Normally if you to this the engine stalls immediately???

jljimenez

You are right, if I push the disk without pushing at the same time the bar that opens the throttle -the same effect that pushing the accelerator-, the engine stalls inmediately.
But when I push the piece that opens the throttle, the disk of the air flow meter goes down a little and the engine hesitates, in that moment if I push the disk with my finger the engine goes up nice.

Sorry about my english, it is not fluent.

bamberger_1

I'm going to check my books to night whether I have an other idea what the cause for the hesitation may be.
Hasta luego
Sorry my Spanish is not good at all

Found another check which might help. Check the temperature sensors. One is in the Air inlet pipe and a twin-type you'll find at the back of the engine block. The resistor value shall be as follows
2800 Ohm @ 20Celsius
1100 Ohm @ 40 Celsius
350 Ohm @ 80 Celsius
Pretty much a lienear function. You need to measure each against ground. Sometimes the wires may be broken. The wires can be checked as follows
one (green red) of the twin type sensors are connected to terminal 21 in the motormanagement plug on the injection controller, the other (green black) is connected to ignition controller (sitting on the driver side fendor).The sensor (blue red) sitting in the air inlet is conneted to terminal 11 of the injection controller. All the sensors have the same charateristic

jljimenez

Thanks Bamberger_1, all these items -about temperature sensors- just checked and they are all right.
Another clue, I have disconected the plug at the throttle and I have made a brige between pins 2 and 3, to simulate that the throttle is always full open, in that way I have noticed the engine has more power when hot, but still hesitates. I am still looking for the air flow meter potentiometer, but Bosh doesn´t sell it indepently -only with the complete air flow meter-

jljimenez

Problem just solved, I got a complete set of air flowmeter and fuel distributor from a sraped car -only 150,00€-, I changed this set and now I have a new car, I had forgotten the power of my motor. It seems the problem was the potentiometer.

Thanks to everybody,

Woody