Rough Idle and CE Light on
Thread Starter
Newbie
Joined: Aug 2010
Posts: 3
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1991 300E
Rough Idle and CE Light on
I have a 1991 Mercedes 300E with over 200K miles. Last month I had an overheating problem so I replaced the thermostat and radiator cap. That seemed to fix the overheating issue, however at one point the vehicle overheated and the engine died. Since then the vehicle idles rough as though it is only firing on 5 cylinders. Yesterday I decided to check the compression to make sure a head gasket wasn't blown between cylinders since there is no water in the oil. All the cylinders were around 120 - 130 psi but when I took out the #3 spark plug, it was fouled. I replaced all of the spark plugs with NGK's (had Autolite in there) and replaced the sparkplug wires as well. The cap and rotor were both replaced about 10k miles ago and still look good. Replacing those items didn't fix anything. If I have the vehicle in park and start it up, it idles rough but if I rev the engine up to about 2500 - 3000 RPM's, it sounds like it smoothes out but not really sure since it's pretty rough until it gets there. What is the possibility of a crank shaft sensor or whatever it is that advances the timing on this vehicle. Oh ya, the check engine light is on all the time now as well. If I checked the code right, it's telling me (10) which is "Throttle valve switch, idle speed contact". Could this switch be causing my issue?
Thread Starter
Newbie
Joined: Aug 2010
Posts: 3
Likes: 0
1991 300E
Since replacing the spark plug and driving the car for approximately 50 miles,I pulled a couple of them and noticed that the #3 cylinder isn't burning. I started the car with the plug out and kept the plug on the wire. The plug is sparking great so my next thought is a plugged injector. I plan on checking the injector this Saturday and will post the results. I also noticed that while the engine was running without a plug, there was no fuel or anything to that matter coming out of the hole. Anyone with injector experience please reply and let me know the best way to clean one. Can I bead blast it or acid bath it or just parts cleaner. Thanks in advance.
Thread Starter
Newbie
Joined: Aug 2010
Posts: 3
Likes: 0
1991 300E
My Theory
Today I decided to check the injectors, mainly to see what parts I need to order. I pulled out the #3 injector and fuel tube. I noticed that at the fuel distibutor, there was no fuel in it after pulling the fuel tube off. I started the car and saw that fuel started to rise up the threads. I screwed the line back on and low and behold the car runs great again. Now for my theory... It looks as though when the car initially overheated the #3 fuel line to the injector vapor locked and lost its prime. By doing what I did, it reprimed the fuel line and started working again. Does anyone know if my theory is right or wrong. Another thing that could have happened is when I was pulling out the injector, I might have freed up whatever was plugging it. Any response is greatly appreciated.
