89 300E, Rough Idle, hard start, stalling solved, thank you all - Mercedes Forum - Mercedes Benz Enthusiast Forums

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Old 09-23-2005, 02:56 PM
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Join Date: Sep 2005
Posts: 10
Default 89 300E, Rough Idle, hard start, stalling solved, thank you all

Thank you to all that helped out with my 89' 300E idle, start, stalling problem.

I will outline all that I did in the hope that it helps someone else, I spent over 12 hours
working on it and hours reading on the net.

Here was the problem:

89 300E, 62K, regular service:
Car started hard, hot or cold, need to give it gas to keep it running. Then once I put it into gear it wants to stall. Once it was running, say a mile or so, car was fine. I started having this problem when my dumb head put 87 octane in it. Since then I have ran cleaner and 5 tanks of 93. Still was happening. I start the car it runs real rough, shaking at idle and at 3000 RPM for a minute then once I take off smooth. But when I come to a stop, it idles a little eratic, 500 - 700 rpm, almost like the AC is kicking in, but it is not.
Anyway, it seams to get worse with the more days that go by.

More: Violent, one time, shake on cold start is a product of a low idle.
When the car stalls in D while driving and then stopping is a result of low idle. It drops to 600 RPM at a stop then will just shut down, like I turned the key off, no rough idle then stall. I simply double foot it and gently press the accelertor to maintain 600 RPM.
It starts easily but idles rough, need to flutter the accelerator to keep it going then brake and accelerate at the same time to put it into Drive or Reverse. Once rolling though, from 600 RMP and up, the car runs great.

OK, here is what I did, in sequence.

- Replaced Distributor and Rotor since it had some erotion in it. Didn't help much.
- Went to Bosch Platinum 4 spark plugs. Didn't help much.
- Tested ignition wires. Fine.
- Cleaned throttle body and butterfly. Helped idle some.
- Tested OVP relay. Tested fine.
- Checked all vacuum with Starting fluid, found hose off Fuel Regulator Valve to Air cleaner housing, easy to accidentally disconect
if not carefull in removing the air cleaner. Check this!
- Tested O2 sensor. Tested fine.
- Ran Chervron Techron complete fuel cleaner. Helped some.
- Replaced fuel filter. Helped a little.
- Cleaned ICV. Helped start problem.
- Cleaned the fuel injectors offline. Smoothed idle out some.
- Adjusted Idle up a hair. Helped start and smoothness.
- Lubed all the throttle linkage and springs, it appeared they were sticking a little causing idle to be eratic some. Helped some.
- Adjusted CO adjustment. With all above and this the car runs perfect.
Starts cold/Hot fine now, idle in P, D, D w/AC, etc. at 600-700 RPM. No
more surging, stalling. Can't tell car is started when at idle in D.

All the above is outlined in various places in this forum, so search for it.
All of the above was just routine maintenance that was needed. Just
bought the car a month ago but with 62K it sat a bunch. 3 last things to check,
for that I see can easily occur: Check for fuel leaks, especially at the
filter and fuel pumps. Check to make sure fuel pumps humm and function, this includes
checking fuel pump relay. Check your injectors offline. On my car they were
part mechanical assist and on one the ball valve was not seating properly causing
a injector leak.... this contributed to hard cold start.

My problem was a combination of things, all stemming from what I believe was crappy,
dirty fuel. Car sitting a bunch before I got it.

Hope this can help someone as you all helped me!
Happy driving!
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Old 09-23-2005, 05:31 PM
Join Date: Aug 2005
Posts: 11
Default RE: 89 300E, Rough Idle, hard start, stalling solved, thank you all

Hi. Very thorough and helpful write-up. I'm assuming re-connecting the vacuum hose made the most difference? Did the CO adjustment help that much? By the way...what CO adjustment? How and where do check that? Thanks again. Dave
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Old 09-23-2005, 06:15 PM
Thread Starter
Join Date: Sep 2005
Posts: 10
Default RE: 89 300E, Rough Idle, hard start, stalling solved, thank you all


Actually, connecting the vacuum hose back to the fuel regulator valve made the car
get worse. I don't know if it was tuned with it disconnected or what.

It's hard to pin-point what made the bigest difference. I know the off line cleaning of the
fuel injectors and changing the fuel filter helped smooth it out.

Cleaning the ICV I think contributed to fixing the hard hot and cold start.

To tweek it all in and tie it all together the CO and idle adjust had a huge inpact.
The CO adjust is the long housing coming off the Throttle body, just to the L/H car side
of the fuel distributor. You access this through the 1/2" hole in the top of the air
cleaner cover. It is adjusted using a 3mm long shaft hex wrench. You need to
push down on the wrench to make the hex nut move down on the spring and contact
the adjustment. It doesn't take much to ruin the adjustment and send ya hunting for
it back so be careful. I don't have a computer or a CO meter for exhaust to monitor
the engine so I did it the same way I adjust my Harleys. I adjusted in Park in idle till
I got a smooth idle. Then I adjusted in Drive at idle till I got a smooth idle, then the same
in D and idle with AC on till smooth. I did a couple rotations of this till I was satisfied with
the performance. Once you make a slight adjustment, let the car catch up with itself for a
second before adjusting again. I think I read somewhere that CW leans it out and CCW richens it.
Maybe opposite, but I was going for performance since my spark plugs showed no lean nor
rich condition. Then I shut the car off and restarted to simulate a hot start and adjusted
as needed. It took a bit and a friend in the car to start the car if I stalled it and to have the
foot on the brake while in D and idling. I put a cup of water on the car and watched the
ripples in it for least vibration and listened also. then goose the gas to ensure no hesitation.
I know it's crude but it worked for me and I also finally passed my emissions test today
for the first time in a month. Guess I got it close.
After all the adjustment I let the car cool then went to start to make sure the cold start was
good. Maybe got lucky cause it was good. Didn't have to go through the whole rotation again.

The car now idles so good even with AC on that I have to look down at the Tach to make sure
it is still running. Those staight sixes' sure are smooth when they run right.

I am going to monitor my fuel economy to make sure that I'm staight.....

Hope this helps!
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Old 09-23-2005, 08:57 PM
Join Date: Aug 2005
Posts: 11
Default RE: 89 300E, Rough Idle, hard start, stalling solved, thank you all

WOW! Another great reason for me to buy a Harley! Where's the wife when I'm all ready to do some convincin'!

OK, my son says I'm patient, but I think you've got me on that. Congrats also for passing the emissions test. I guess when everything's going right....

Thanks so much for the info. I'll bet it helps many. Dave
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