70,000 km / 45,000 miles on the clock, service up-to-date. Daily driver and a great ride.

Starting few weeks ago, car would occasionally (about once or twice a week), have difficulty with cold starts:

- engine would not catch on 1st crank, then start up as normal on 2nd crank;

- engine would catch on 1st crank, but stumble then surge for a sec. The surge takes the rpm to about 1,500 mark (normally should be around 1,000 ?), before settling down to the usual idle speed.

No Check Engine Light at all, and the car otherwise runs fine.

Warm/hot starts are always good, one crank.

What may be the problem ?

Throttle Actuator (big $$$) starting to go bad ? Or something minor to leave alone for now, taking it to the shop if it gets more frequent ?

Thanking in advance.

There is a tech service bulletin which may be applicable. Text is as follows:

03/95-2 M104 WITH HFM INJECTION SYSTEM


In case of customer complaints of high idle (approximately >2200 rpm) for a very short period of time (< 1 second) immediately after cold start, an updated EA/Idle control unit is available from our PDCs. The updated control units can be identified by a software production date of "SW 43/94" and higher stamped on the housing in the area of the barcode label. The following control unit part numbers are affected:

Electronic Accelerator Control Units

Part No. 124 545 65 32 - E320
129 545 05 32 - SL320
140 545 49 32 - S320
202 545 01 32 - C280

Idle Control Units

Part No. 124 545 55 32 - E320
129 545 19 32 - SL320
140 545 52 32 - S320
202 545 43 32 - C280

Thanks to J.M. for the detailed response.

The symptoms have changed since my original post, now not quite mapping to the bulletin that J.M. kindly clipped.

Current situation

1. cold starts - normal

2. hot starts - normal

3. warm starts (say more than an hour after shutting down but before engine completely cools) - 1st crank engine spins but does not fire up. 2nd crank engine starts, stumbles, rpm shoots up to about 1000-1500 for a sec, then settles down to the normal 500-600 range.

The car otherwise drives well as always.

Read in the archive that OVP & Throttle Actuator are common failure items on the W124 / M104.

The OVP is easy to replace DIY... but if it is really the culprit will engine crank at all ?

I won't be able to replace the Throttle Actuator myself, but as it is a big $$$ item would like to know if this is something that is possibly at fault here.

Thanks again for all advice.

Sure...OVP has nothing to do with starter circuit.

Any chance you can build the "Radio Shack" code reader tool described on this site? It will be very difficult for anyone to help you without some more diagnostic information. Also, has the engine wiring harness on this vehicle ever been replaced?

Thanks again for the tip J.M. Engine wiring harness replaced in 2003.

I wouldn't be able to build the code reader based on my current knowledge levels (and not much spare time available to train up).

The starting problem has grown more frequent now, happening daily with hot or warm engine. Only cold start is good.

Will be taking the car to the shop & post back on the remedy. Hopefully it's not the throttle actuator. Cruise control works fine all along.

Impala,

I have the same year/model car and the same problems on cold starts. I replaced wiring harness and main computer this year ($$$$). I thougt the cold start isue was normal.

Please let me know if you get any solution.

thanks

Juan

The fuel pressure regulators are known to fail on the M104. Typical failure symptom is excess cranking required. Poor mans test is to pull the vacuum tube and smell for gasoline fumes. Real test is to attach a fuel pressure guage and measure pressure bleed down. Replacement, if required, is ridiculously simple.

- JimY

Thanks Jim. Beginner question but where is the regulator located and what does it looks like?

__________________
-----------------
Juan
1995 E320 Sedan
2008 Ford Escape
RC Helicopter

It is located at the rear end of the fuel rail (providing fuel to the injectors). It has a manifold vacuum line to the top and fuel return line at bottom.

Anyway, the slightly harder start when warm (due to engine temperature or weather) is because the fuel system looses its pressure when engine is off, allowing fuel to evaporate inside the fuel system and cause "bubbles" in the fuel, which must dissappear before the engine will willingly start.

The leak can be anyware, but the fuel pressure regulator is definitely a good point to start. Another point is the check valves at the output of fuel pumps.

__________________
1991 300SEL (W140)
1987 190E 2.3 (W201)
1987 Honda Accord 2.0

The symptoms were changing in past few weeks, latest was that only HOT starts were good. Cold starts & warm starts required excessive cranking and had to stepped on gas a bit to get engine started. RPM would shoot up to about 1,500 for a sec before settling down.

Had the car back from the shop for 2 days now, so far fix has been good.

Diagnosis : Fuel Pressure Regulator leaking fuel internally.

Solution : replaced the regulator (000-078-18-89).

Thanks again for everyone providing advice !