90 300SE Start / idle problems
Thread Starter
Member
Joined: Jun 2003
Posts: 130
Likes: 0
From: Northeast MA
1990 300SE
90 300SE Start / idle problems
Hi,
The car is a 1990 300SE with 189,000 miles
This past winter the car would not start in the
morning when it was about 15 degrees F or lower out.
Car would turn over but would not start. On 3
occasions I had to add 2-3 bottles of dry gas each
time for it to start. Also recently the engine seems
to start rough in normal weather and idles roughly.
Once the car is going about 10mph it is as smooth as
glass without any hesitation, surging or misfires.
Engine does not smoke at all. Changed out fuel filter
and that did not help. Platinum plugs, wires rotor
and cap were replaced about 60,000 miles ago. New air
filter, EGR valve and O(2) sensor on 11/02,
When my car was in for an alignment at my local MB
dealer, I had them check out the car’s problem. An
initial diagnosis was performed but the technician ran
out of time. Below is what was written on the service
receipt.
“Performed lambda test, found intermittent
reading-possible control module for cold start
problem, may need fuel distributor and injectors,
possible coil”
what and where is the control module? Is it the engine
computer?
What are the symptoms for replacing a fuel
distributor? That is one expensive part!
When should injectors and a coil be replaced?
I figured the coil is fine because there is no problems
at above idle speeds.
Any help is appreciated, I really do not want to put
much more money into this car.
The car is a 1990 300SE with 189,000 miles
This past winter the car would not start in the
morning when it was about 15 degrees F or lower out.
Car would turn over but would not start. On 3
occasions I had to add 2-3 bottles of dry gas each
time for it to start. Also recently the engine seems
to start rough in normal weather and idles roughly.
Once the car is going about 10mph it is as smooth as
glass without any hesitation, surging or misfires.
Engine does not smoke at all. Changed out fuel filter
and that did not help. Platinum plugs, wires rotor
and cap were replaced about 60,000 miles ago. New air
filter, EGR valve and O(2) sensor on 11/02,
When my car was in for an alignment at my local MB
dealer, I had them check out the car’s problem. An
initial diagnosis was performed but the technician ran
out of time. Below is what was written on the service
receipt.
“Performed lambda test, found intermittent
reading-possible control module for cold start
problem, may need fuel distributor and injectors,
possible coil”
what and where is the control module? Is it the engine
computer?
What are the symptoms for replacing a fuel
distributor? That is one expensive part!
When should injectors and a coil be replaced?
I figured the coil is fine because there is no problems
at above idle speeds.
Any help is appreciated, I really do not want to put
much more money into this car.
Newbie
Joined: Jan 2003
Posts: 9
Likes: 0
First thing I'd do is get rid of the platinum spark plugs. There's alot of bad history regarding the 103 MB motor and plat plugs.
Use the std. Bosch copper H9DC0 and gap at about .036 or so. The factory gap calls for .032. Some guys go as high as .040. I set mine in the middle at .036 and have a pretty smooth idle.
Use the std. Bosch copper H9DC0 and gap at about .036 or so. The factory gap calls for .032. Some guys go as high as .040. I set mine in the middle at .036 and have a pretty smooth idle.
Newbie
Joined: Jun 2003
Posts: 4
Likes: 0
From: NJ
1987 560 SEL
If the car idles and starts well when warm (you didn't mention), that would sounds like a leaking cold start valve to me. I'd start there. Its an easy swap, maybe $140 USD for the part.
If the car idles rough in general, I'd yank the plugs and look for a fouled plug. If you find one, replace it or clean it and check again later. Could be a leaky valve. With that many miles, you're due for valve stem seals at least.
I agree. Plat plugs are junk. I'd scrap 'em.
Always good to get a second opinion though.
Regarding the service report, they listed everything imagineable. That's akin to "Rough idle cause by faulty fuel delivery system".
Typical bogus MB service. Remember these guys aren't MB experts. No MB dealer seeks out experienced mechanics to work on new cars no one has ever seen. They are trained to do warranty work on new models. Warranty work is R&R (remove and replace). I think you would be better off with a personally recommended Bosch certified private shop. Just don't expect them to pour you coffee or wash your car!
Adam
If the car idles rough in general, I'd yank the plugs and look for a fouled plug. If you find one, replace it or clean it and check again later. Could be a leaky valve. With that many miles, you're due for valve stem seals at least.
I agree. Plat plugs are junk. I'd scrap 'em.
Always good to get a second opinion though.
Regarding the service report, they listed everything imagineable. That's akin to "Rough idle cause by faulty fuel delivery system".
Typical bogus MB service. Remember these guys aren't MB experts. No MB dealer seeks out experienced mechanics to work on new cars no one has ever seen. They are trained to do warranty work on new models. Warranty work is R&R (remove and replace). I think you would be better off with a personally recommended Bosch certified private shop. Just don't expect them to pour you coffee or wash your car!
Adam
Thread Starter
Member
Joined: Jun 2003
Posts: 130
Likes: 0
From: Northeast MA
1990 300SE
Thanks for the input guys. I am going to start with changing out the plugs this weekend and inspecting the cap and rotor. The valve seals were replaced at about 90,000 mile because it was using a quart of oil every 800 miles. Now (100,000 miles later) it uses about a quart every 1200 miles. It does idle rough when warm, the engine shakes but the tachometer stays steady. I was told it is caused by bad engine mounts but I replaced them last year along with the engine shocks. It didn't stop the vibration at idle. Besides the very cold starting problem and the rough idle, it runs as smooth as silk. Just underpowered around town.
Dan
Dan
