89 300sel surges at idle, intermittent... I've read, and read.. Help please?? - PeachParts Mercedes-Benz Forum

jay3000 · #1 06-23-2003, 02:11 PM

Engine runs well otherwise, but on some occasions, it will have a rythmic surge at idle, especially when in gear. Sometimes it runs beautifully, and idles smooth as silk.

All tune up parts are relatively new, and even has a new O2 sensor. I removed, and cleaned the idle control valve with throttle body cleaner. It wasn't very dirty, and seemed to have no effect.. The OVP relay is apparently the old style with one fuse, but the ABS light has never come on, which leads me to believe it's OK..

This seems to be a common problem, as there are plenty of posts about it, but I can't seen to find any posts where someone has found a successful cure..

Anyone know where I need to start looking???

THanks,
Jay

terminator · #2 06-23-2003, 02:46 PM

I had the same problem with both of my 300SELs. My current one is an 89 300SEL. I had a cold idle problem that turned out to be my Air Flow Meter. Whem my tech replaced it, it also fixed my surging idle. What appears to happen is the meter gets a burn mark on it at the idle position, and it searchs for the right idle. You can have it checked to make sure. It is expensive to replace so its not a part you want to just try out.

jay3000 · #3 06-23-2003, 02:53 PM

Where exacly is the air flow meter located on this engine??? I'm still trying to make the transition from GM cars, and Jeeps...

terminator · #4 06-23-2003, 03:35 PM

The fuel distributor and of course the breather sits on top of it, it is silver and has a round opening with a trottle plate door.

jay3000 · #5 06-23-2003, 03:44 PM

Thanks Termintor..

I found a picture.. It looks like more of a throttle position sensor, than an actual air flow meter.. I'm starting to figure this car out now.. Maybe I can do the quick eraser fix, and sell it before it ends up costing me a fortune.. I really like the car, but instead of nickle, and dimeing me to death. Everything costs a couple of hunderd dollars..

It's a beautiful car otherwise.. It scares me though..

terminator · #6 06-23-2003, 04:03 PM

Don't let it scare you, out of the Mercedes that I have owned it has been one of the least expensive ones. In fact I might be getting a third one. It is a 1991 300SE. The inline six you have in that car is very easy to work on. A old Mercedes fuel injection system is a lot different than the American ones. I have seen a few 300SE/SELs with about 300k on the clock.

sbourg · #7 06-23-2003, 07:27 PM

The plate you see on the airflow sensor is not the throttle valve. It is the airflow sensor plate that is deflected depending on engine air demand. It is in no way connected to the throttle linkage nor does it control the airflow. The pot on the side sends a signal to the ECU which tells it when enrichment is needed, based on how quickly its value changes.

Steve

jay3000 · #8 06-24-2003, 08:14 AM

I just assumed that that was like a throttle plate, and was connected to the linkage.. I'm so GMish..

Steve I'm following your post about the airflow pots, and will have a coule of questions that I hope you or somene else will be able to answer.. I plan to order it, and replace it. Mine looks original, and is surely worn out. That's bound to be what is causing my surging idle..

THanks for thr help,
Jay