300e Very Rough Start, Dies HELP PLEASE
 

Hi all,
Well, here is the problem du jour with my 87 300e. It has had a rough start when warm for the past few months, on and off. This means that the engine starts up clattery and rough, vibrating the car, but only occasionally. But today, it seems the problem worstened. The car started, got to idle, then would drop in idle speed way low, quite below 400. It made a loud rough hissing noise as doing so. Then the idle came back up. After a few starts, I found that sometimes it will drop and die, but mostly it drops and goes back up, up to 4 or 5 times in succession. I am concerned to say the least, especially about the noise and its implications. I've searched the archives and it seems full of people saying its the OVP, and then those with the problem saying changing the OVP did nothing. Can anyone help???????
Thanks
Scott

what is your maintenance history?

where and when do you get it serviced?

have you had a MAJOR tune up lately?

what is the mileage?

peter

Sounds like a internal fuel leak and a gummed up ics valve. Try running a couple cans of techron through it, reset the base CO and cleaning the ics. (along with some new plugs and secondary ignition inspection)


Joe

The car has 142,200 miles on it and has had the 15k at 135 and I am just about to do the lube. I've owned it for a year and have serviced it at a dealer. The lube service and other minor stuff i do myself. When I was looking around the engine compartment this morning, I thought i did smell a little whiff of gas, so that may be part of it. joe p, how do you reset the base CO and clean the ics?
I am going to get Techron and run it hard this afternoon. Thanks again for your input

what i am wondering is if you have had the [every] 30k maintenace done?

including [in this is] new plugs, fuel filters, etc.

it may only need a good service.

peter

nope, the 30k is coming up in 7500. It also did it today when I was sitting in traffic for 5 minutes at operating temps. When the dealer did the buyers inspection, they found that the car might need injectors because it ran rough. I later found that it really needed the O2 sensor replaced and did so. Could the injectors be at fault? Peter, would you recommend that I move up the timetable on the 30k?

it couldn't hurt.

imho- preventative maintenace is critical.

i always have my maintenance done a little early.

peter

Defintely do the double-Techron dose in a less-than-full tank of fuel. The richer the mixture the greater the cleaning, within reason.

Have you checked your cap and rotor?

My take is dirty fuel system/injectors. Another tip is to CAREFULLY bleed the injector lines at the fuel distributor. A tech recommended this for the 190E. I did it twice and bled all sorts of crap out. I was really amazed.

Someone recently with a 420SEL with one clogged injector did this with good results

Keep us posted,

Haasman

hmm, well, the problem is worse than I thought. It did the same thing this morning at 30 degrees on a cold engine so temp doesn't matter. The car will start on the first or second try, idle for a bit, and then do it's bucking bronco routine. The rpms drop, the engine makes a loud hissing and it comes near stopping. Often if you do not apply the throttle it will stall out. I took out the ignition control valve and cleaned it with about a can of WD40, a very slight exageration, to no avail. I have techron in, but filled it up before I put in the Techron. I will wait till its got a quarter tank and dump in another two bottles. I am 17 and not rich enough to own this car, so anything I can do on my own would be of great help. Haasman, I will try bleeding the injector lines if I can figure out how. Thanks for the info all!!!

Bleeding the injector lines is easy. Find a wrench that fits the nut holding the injector lines into the fuel distributor.

Caution: A running engine with raw fuel coming out can be very dangerous. Be very careful.

Haasman

Hissing sound? could be a vacuum leak - classic cause of poor hot starting and rough/uneven idling in any car.

Check all vacuum hoses for splits/leaks.

The car makes the noise only when the rpms start to fluctuate. It sounds like a severe hissing sound when inside the car

Drove home from work, pulled in, let it idle for a while at 90c coolant temps, did fine. Turned it off and restarted. Idled rough but didn't cut out, but when I shifted back from drive to park, it stalled. tried same test three times with same result.

resetiing/checking the base CO is easy. Warm it up, place the + lead of your DVEM in pin #3 of the diag socket (round thing on the l/h inner fender near the EZL) ground the other, set it to duty cycle and watch it idle. You should get a reading close to 50% with a 5 tto 10 swing. (depending on the system and speed of your dvom) 3mm allen in the center of the air cleaner is the adjuster, the tower for the adjuster might be plugged. Get creative getting the plug out, towers are cheap if you demolish it, just keep the metal out of the engine)

Personally, I'd get a tech to resset/check this as getting heavyhanded here could get expensive.


Joe

Re: 300e Very Rough Start, Dies HELP PLEASE
 

Hi, Have you discovered the source of the hissing?

I've experienced the same on my 1979 450SLC, in the past. Car would run OK, but would suddenly develop severe loss of power accompanied by loud hissing. Then the problem would go away.

Now, after sitting for a few months, the car will not start, and the mechanics found very low flow to fuel injectors (primary fuel pressure is 75 PSI, control pressure on cold motor is 18 PSI, both apparently in spec, ruling out the Fuel Pump and the Warm Up Regulator as culprits) along with polluted fuel coming from the one of the fuel distributor injector lines (the one they opened).

My guess is that the upper chambers in the FD contain polluted fuel with gunk and sediments. On a running motor, this might throw off the FD fuel metering and interfere with the control pressure, thus forcing the air flow meter plate into a different position (in relation to the air flow) – probably to be very close to where it sits at idle - by allowing the FD plunger to position itself too low within the FD in relation to the fuel demand of the running motor. The combination of fuel demand, at given RPM, with an almost closed off air-flow sensor plate is what I suspect is the cause of the hissing. This is consistent with a severely degraded power output at those times.

In my case, if the hypothesis of the problem is correct, I will need to bleed the FD in hopes of dislodging the polluted fuel. It is likely that the injectors have also plugged up and will need cleaning or replacement. In case of you motor, the cure is probably the same, assuming the diagnosis is correct, except that in your car the situation has not gotten to be as bad as in mine.

I’d appreciate any feedback.

Cheers