Originally Posted by arkie (Post 2118526)

I have a 1993 190E 2.3 8V that started a consistently high idle suddenly a few months ago (circa 2,000 rpm free idle once warmed up, in P or N, 1,000rpm in gear). I parked it due to high braking effort needed on the 20 stoplights between home and work. Here are my observations so far.

• Cold idle around 1,200rpm when cold, then it as it gets up to temperature the idle increases to 2,000rpm.

• I can shut the car off, immediately restart it, and the idle is around 1,000 rpm.

• OVP was checked by Indy this past week and replaced with a new one, no change in idle behavior.

• I can push back the linkage slightly to change states of the cut-off switch for idle, and the idle changes slightly so I feel that switch is functioning.

• Measuring pin 3 to ground on XD11 connector gets near battery voltage (about 12 volts compared to around 13V for the batter) - means its running a consistently rich mixture from what I can glean from the myriads of discussions I have found To check the duty cycle on pin #3 on the Diagnostic Connector, you have to be in the diagnostic mode. I just went through all of this on my '93 2.3 to isolate a low idle problem. I built the LED tester that has been discussed on this forum, then I was able to read DTC codes and put the engine into diagnostic mode to check the duty cycle. By doing this, I retrieved the codes and found the problem.

• I had to replace the original catalytic converter last summer

• O2 sensor hasn't been replaced in the time I have owned the car (got it at 121K miles and it has 188K now)

• I replaced the spark plugs yesterday to see if it helped, old spark plugs were worn but didn't look bad - pretty good uniform brown color with a little blackening that wasn't objectionable.

I'm stumped and my Indy is stumped - do I need to replace the O2 sensor so that the system isn't running it rich and increasing airflow to compensate for the extra fuel, or is the O2 reading a rich mixture properly and I just need to adjust the mixture on the tower on the airhorn, or am I completely misunderstanding whats going on here and there's another issue? In my opinion, DO NOT ADJUST THE AIR/FUEL MIXTURE. It won't correct your idle problem.

The first thing I would check is the operation of the Idle Control Valve. When you first turn the ignition on, the inside flap is slammed to the fully open position, then it is suppose to release after 10 seconds. If the inside is gummed up, they sometimes stick and cause a high idle. I can duplicate your problem by applying battery and ground to the ICV and the idle goes up to about 1800-2000 rpms.
When I first start my engine at cold, the rpms are about 1000, then after 28 seconds it goes down to 700-750 and stays there when I put it in drive and/or turn on the A/C.
You can remove your Idle Control Valve and look inside to see if it has a small opening when in the off mode. Then, take a 9v battery and touch it to the contacts to verify that the flap is opening then closing when the battery is removed.