'91 300SE hesitation- possible clue ? - PeachParts Mercedes-Benz Forum

microtoad · #1 12-22-2005, 07:34 AM

I have been having intermittant hesitation problems on my car. Sometimes it seems like the accelerator pedal is not connected to anything. Yesterday I was out shopping all day and the car ran perfectly. Late in the day I decided to wash the car to get all of the salty road spray off. I went to a you wash it place with the hand held sprayer and tried my best to get the car exterior clean as well as spraying the wheel wells and underbody. When I left it started right up but as soon as I turned onto the main road I noticed the hesitation. It was worse than ever and I was worried I wouldn't get home.

It's like when you have a car with a carburator and the accleration pump is bad. You step on the gas and nothing happens (no squirt of fuel down the venturi's), then it slowly builds power until you are driving normally. The little vacuum gauge in the instrument cluster swings over to to full right so it appears the throttle is opening up, just no fuel. I assume water has gotten in somewhere. Any suggestions on the where to look for the offending component/connector ? I thought possibly the idle control valve. It is more towards the front of the engine where it can get wet. Possibly the fuel pump connections ?

One more clue. Every now and then the car hunts for the right idle point. The tach needle tends to bounce up to 1300 then fall to 600 then bounce up to 1300 and so on. Slowly the oscillations dampen and it finds the right idle at about 600-700 RPM.

Any suggestions to point me in the right direction would be apreciated.

preban · #2 12-26-2005, 11:12 PM

Hi micro,
I had the same problem with my 89 300se a few weeks ago. From a dead stop I'd put my foot in it ( a little) and the car would hes..i..tate andthengo. I enriched the co mixture a little, maybe an 1/8 of a turn. Checked for vacuum leaks as well, some of the hoses were cracked and replaced those. One other thing I found as I was greasing the throttle linkage was that I wasn't getting full throttle. There's a ball joint that fits right into the firewall on the linkage, it had popped out so I replaced that. Now I have great power and acceleration. Hope this helps!

How's the mileage on your car? I'm getting around 14-15 mpg and I'd like to think I could get better.

wbain5280 · #3 12-27-2005, 01:46 AM

Check the coil wire where it clips to the distributor, under the cover. Mine was almost burned through and a little Locktite 5900 on it has helped. I really need a new coil wire.

haasman · #4 12-27-2005, 02:00 AM

Pull the air cleaner and make sure the air sensor plate is clean. Often with a lot of crud it will reduce throttle transition respones.

Haasman

microtoad · #5 12-27-2005, 06:38 AM

Thanks for the feedback. I'll take a look at your suggestions this weekend. I didn't consider the coil/wire as a possibility.

Preban, I monitor fuel mileage fairly closely. Last summer, in the heat, I was running just under 20 mpg (very little a/c use). In the bitter cold of a Minnesota winter I have dropped into the 14-15 range as you point out. It seems like a pretty dramatic change. I replaced the air intake temp sensor a month ago and thought that may have something to do with it. Perhaps the mixture needs to be recalibrated with a new temp sensor ? I also replaced the thermostat with a 90 C unit. No help on the milage but sure helped the heat in the cabin !

Ferdman · #6 12-27-2005, 06:55 AM

Gas formulations for the Winter result in reduced mpg ... not sure if it accounts for a 25% reduction though.

gmercoleza · #7 12-27-2005, 09:17 AM

I would think winter mileage would increase or at least stay the same, due to the a/c compressor not running...

Moneypit SEL · #8 12-27-2005, 10:49 AM

Quote:

Originally Posted by gmercoleza

I would think winter mileage would increase or at least stay the same, due to the a/c compressor not running...

You would think wrong, then.

In addition to winter-formula gasoline, engines take longer to warm up, and thus stay in cold enrichment mode longer. Not to mention folks (like myself) who let the engine idle while cleaning ice and snow off the windows.

preban · #9 12-27-2005, 10:59 AM

I kinda figured that the weather probably affected the fuel injection but I was hoping that perhaps there was an "adjust this by 5 degrees" fix to compensate. Also, seeing as how my 300se is running without a catyltic converter that might affect the injection, too.

Let us know how it turns out micro!

bdlefferts · #10 12-27-2005, 10:59 PM

microtoad, I too had hesitation problems a few months ago. I took off my distributor and found that my camshaft seal was leaking. I had a gritty/oily mess in the distributor cap. One of my sparkplugs was bad. After installing new sparkplugs, camshaft seal, rotor & distributor, the car was running smooth again. Recommend you check the basics first.