poor gas milage and lack of power please help - PeachParts Mercedes-Benz Forum

Victor300E · #1 04-06-2005, 04:53 PM

Hi everyone. I bought 1990 300E with 179k miles. Car is in good shape but Im wondering. My gas milage is aroung 13mpg combined city/highway. And car kinda
slow at pickup. Sometimes it moves very slowly then suddenly 1st gear kicks in and it jumps forward. I had 420sel before and it used to be slow off the start. But I heard that 300E should be quicker. Also when you change from reverse to drive RPM drop down to 350 and car almost stalls then RPM goes back up to 500. When cold its better to pick up speed and RPM will not drop down that much. Im in NYC and gas prices are high in here well I guess all across US now but 13mpg is too low I think. Apreciate any ideas. Thanks

A264172 · #2 04-06-2005, 05:17 PM

Did you get any records with the car?

It could be a lot of things... from a colapsed Cat

to just a new O2 sensor and a tune up.

Based on your symptoms you might want to start with the cat... by disconecting it or the pre cats from the exaust manifold and straping the pipes to something... then test drive and see if it solves your power problem.

Victor300E · #3 04-06-2005, 09:08 PM

I got dealer book with oil changes recorded until 120k miles but nothing major like timing chain or other repairs are not listed. I have some receipts from various shops stating brakes,oil changes,ball joint. Ive changed 1 motor mount(it was collapsed).I changed spark plugs and they looked original. I opened distributor cap and cleaned terminals because they also looked original. I dont think its a great idea of grinding terminals since theyre should be gaped I believe. well after cleaning car became a tiny bit smoother. Thanks for cat tip. Ill try to unbolt pre-cats off exhaust manifold and drive around (maybe Ill like the noise and leave them hanging "dragster wanna be"

I want to check for vacuum leaks around idle air valve. How do I do that? Is there a place I can connect a vacuum gage to check for specific vacuum number and what will that number be? Thanks for help

G-Benz · #4 04-06-2005, 10:12 PM

Without a proper and thorough diagnosis, it's a crap shoot trying to get a definitive solution to your problem. A proper approach is to start by checking ignition components, followed by emission equipment, then fuel system related items.

But since you are getting all sorts of advice thrown at you, I would venture a guess that your MAS (mass air sensor) is bad.

Victor300E · #5 04-07-2005, 08:52 PM

I ordered rubber hoses for idle air control valve. There must be leak there when I checked spraying carb cleaner on them. I also cleaned distributor cap and rotor for now until I get new one. Ill check how strong the spark is tonight. Its getting dark outsie so it will be visible better than on sunny day. I would really like to check compression but have no time I come home late and shops are closed by the time. Also I think gutting out my cat. car has 180kml so Im thinking to gut out my cat would not hurt it

My cat is very loud comparing to my Olds minivan. Mufflers were replaced 6 months ago by previous owner ( I have receipt) so there is a chance of cat being cloged or broken inside not lettign exhaust gasses to pass freely. And of course since I dont know if fuel filer was changed Ill change it as well. It would be nice to diagnose all suspecious components with speacial tools but I cant. Im street type mechanic. I have basic tools and some jack stands and jack. It might sound little but I took off my old 420sel transmission off on the street, rebuilt it down the basement and pt it back, drove the car with no problems for a year then sold it

I loved that car. I had 2 tone interior in it in mint condition but car developed some rust in rear. I dont do body work so I had to sell it. Sorry for long post but if you guys think I should check something elso or I overlooked something that applies to my above stated proiblem please let me know. Thanks
Victor

A264172 · #6 04-08-2005, 12:04 AM

Sounds like your doing pretty well so far... like G Benz says no point sealing up your window if there is a hole in the wall. You might want to look into a few diagnostic tools like a $30.00 multi meter with duty cycle if your vacuum leaks
and spark clean up dont help. It will pay for it self after you don't through one $40.00 dollar sensor at it that you don't need.
Report back on your results... that vac leak sounds promising... 179,000 miles is brittle time for those hoses.