Klrgator

I´m having issues with my E320 1997 W210 at idle. Seems to be that randomly it seems to stall and get back to normal idling RPM. The car will perform flawlessly at any other RPM without power loss or any hesitation. It is only at idle where it randomly tries to stall and comes back.
I have never experienced this issue before. The car has relatively new spark plugs and spark plug wires (changed a couple of years ago), changed also two of the three dual coils and cleaned the Mass Air Flow Sensor about two years ago too.
I usually put only about 4,000 miles a year on this car.
The issue only happens at idle. I don't have the "Check Engine" light on at all.
Does any one has an idea/suggestions where should I start to troubleshoot?

I´d appreciate very much your ideas.

Thanks!

Plutoe

If you have a M112 and the diagnostic equipment you will no doubt find the fault-----however your idle speed control is established by and controlled thru the ECU which receives data from the pedal position,coolant temp, O2 sensor and throttle body actuator(rather complicated) to establish an engine idle speed.
Your problem is that the only sensor that will produce a fault is the O2 sensor,therefore you can eliminate that. Plus if the dash is properly reporting the correct coolant temp, you can eliminate that sensor. You are now left the other sensors plus the ECU as suspect,however without the diagnostics I do not know how you would go about testing.
The other interesting issue is cost.The ECU and throttle body which contains the actuator are valued more than your twenty one year ole cream puff---so hurry up and start testing.

kajtek1

What Plutoe was trying to say - your car is first generation of computerized engine management and lacks some programs later models do have.
When bad CPS will not show error on this car - bad PPS will trigger CEL and that error happens usually when you floor it. Meaning you can eliminate that one as well.
Still you should always start troubleshooting with code reading (even when there is a chance you might not have them).
Your car require 38-pin scanner plug for full reading, but even with standard OBD you might get something.

machadosl

One of the causes of this symptom without showing the engine light can be a false air intake in by some hose, verify any that goes to the intake of the engine starting from the air filter compartment.

Klrgator

Dear Plutoe, Kajtek1 and machadosl:

Thanks for your answer.

I have the M104 engine (six cylinder in line) and not the M112.
This is a strange issue since the car runs perfect at any RPM above idle.

The temperature is being reported properly.

I have a friend with an ODB scanner. I´ll plug it in and read any codes that may happen. I did use this scanner in the past and helped me to solve a "Check engine" light (issue with the cam positioning sensor) so I´ll give it a try.

I´ll also check for any possible "false air intake" between the air filter and the intake of the engine.

I will update my findings.

Thanks again!!!

kajtek1

Like pointed above - OBD scanner will not read advanced codes on this car. You need one with 38 pins.

machadosl

I just forget to write, verify also the fuel pressure regulator that is going warn or the fuel pump. You will need a pressure gauge to verify.

Klrgator

Finally found the problem!!

After driving the car for several days and having this fiddling issue, the problem started to become more noticeable at all speeds until a Check Engine light came on.
I got a "P0306 Generic Code Cylinder 6 Misfire Detected". Based on this I checked the spark plug (which was changed when I changed all the spark plug cables), as well as the condition of the rubber plugs that are attached to the ignition coil that fires cylinder 6.
After all these tested OK, I replaced the ignition coil that controls cylinder 6 and cylinder one (this car model uses one coil for every two cylinders) and the problem got away!!!

Thanks everybody for your comments and help!!

machadosl

Nice! Thank you for the solution!