I replaced the MAS on the cross over and finally got definite confirmation the Wire Harness is a good replacement (thank God). Other than plugs and wires what have you guys run into that will give a rough idle. The weird thing is yesterday for about 2 or 3 hours the idle was perfect then when I started her up again today it was rough. Any ideas are welcomed.

Thanks

 

When you say rough, does it feel harsh like a small jackhammer? Does it vibrate inside the car at a stop? Does it feel much better in park that in drive and get worse as it warms up outside? If so, that's the passenger side engine mount.

When you look at the engine, is it shaking noticeably? That's something else. If yours is shaking I'll see what I can come up with.

 

OVP Relay, Motor Mounts as previously stated, Idle control valve, vacuum leaks, and of course your regular tune up parts are a good place to start (cap, rotor, plugs, wires)

This seems to be so common on these cars that I have grown to hate the CIS-E injection systems, which if non of the above solutions fix your problem could be very expensive to fix.
My summer project will consist of a Megasquirt stand alone engine management system converting to electronic fuel injection as well as electronic distributorless ignition.....and wahlah! No more problems!

 

Idle a bit better in park and gets rougher as the car warms up. I am going to do the motor mounts cause they are do.

 

The fuel filter is very often neglected and vacuum leak is also a possibility. And doing a compression test might also tell you something about the engine´s condition.. - Just some thoughts..

Cheers,

 

I should also add leaky valve seals to the list.

 

You most likely only need to do the passenger side. It breaks down due to the heat from the exhaust manifold. The one on the driver's side will probably outlast the car.

Also FYI- your car does not have CIS-E injection. Yours is the HFM system. There is no cap and rotor, and I believe the idle is controlled through the electronic actuator.

 

I second that....I wasn't particularly looking at the year of your car.

 

Today I am throwing some spark plugs at the situation. Figured I should try the cheapest thing first. I half to return the RESISTOR style plugs I was given at the parts store and get plugs that won't fry half of my ignition. I am realizing quickly that the folks there just don't know these cars enough to give me the correct parts for the car.

 

Well, yeah- they were still in diapers when it was made!

 

Day and a half after the use of Seafoam which I put in the gas tank and in intake manifold on my 1992 300E I started having idle problems, it begun to have rough idle intermittently. It was progressive, the fourth day of use it was really bad, it would stall and loose at least 30% of power. While driving I exercised the gas pedal and found positions where it would run very good, but as soon as I got to a stop the engine would tend to stall and idle would be very erratic, engine would stall and loose at least 30% of power. I could also smell stinky sulfuric gases from the exhaust and when hot some plastic overheated smell from the catalyst converter. In the morning during cold start idle was ok, but as soon it warmed up to about 70~80C (when it went to idle) it would begin very erratic again. First thing I thought I clogged or contaminated the fuel injection system with debris removed by the Seafoam, so I drove it in the highway until I burnt most the gas in the tank, refueled then took it for a ride no help, it behave the same. So I decide to remove and clean all injectors in ultrasonic machine, no help
I replace the fuel filter no help
I read the lambda ratio on pin 3 of X11, and I could see that the voltage would read 7~7.5Volts while warming up and would drop almost to ' 0' volts when warm (70~80C)
I checked all vacuum connection, temporarily strangled some, no difference.
I read the error codes out of pin 3 of the OBD1 connector (Fuel Injection controller) and found no errors.
I read the error codes out of pin 14(MAS controller) of the OBD1 connector and found no errors.
I checked the ICV and cleaned as well, no help
I replaced all spark plugs and verified operation of the cables, spark was getting there.
I disconnected and checked the EHA with an ohmmeter and found ok.
I checked the coolant temp sensor resistance (double sensor) and it read normal for the temperature.
I disconnected the coolant temp sensor and put two 2500 ohm resistors across to the pins of the coolant sensor connector to fool the computer (as if engine was cold), no help. engine would still misfire and be very erratic.
I checked the voltage out the oxygen sensor which read ok while warming up (0.4~0.6 volts), then would drop to ' 0' at normal operating temp.I disconnected the O2 sensor while running, no help.
Car ran so erratic that it made me believe that the ignition timing was being shifted by the computer.
I hooked a strobe light and verified that the ignition timing was correct (10~12deg BDT), and it would not change from cold to hot operation of the engine.
I decided to put an inline spark monitor on cylinder #1 to observe the spark and eureka !!!! it fixed it. It was the connector pipe on cylinder #1, I don't know how it affected seemed like all cylinders, remember one of the things I did during my troubleshooting one day when the idle was messed up was to pull each spark connector at a time to see the effect and I could not see a significant drop on any of them. Anyway to be 100% sure of my findings, I removed the inline spark plug tester hooked the pipe back and there it failed immediately, then I put the inline spark tester, took it for a drive and worked perfectly, so I order a new pipe connector for cylinder #1, a U$14 part and problem solved.

 

.....
..... what is this pipe connector you refer to? I'm completely lost!

 

I am having what appears to be the same problem. In my c320 - 2002. Car sometimes idles fine other times it about dies when slowing to 2 mph or less or stopped. Recently replaced Oem gas cap. Ran fine for 4 months. What is the pipe connector?

 

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