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Subject vehicle is a '88 190E2.6 with a (very rare) five speed manual, 73K miles, original owner.

The following questions/ issues are probably common to all models with the 103 engine, and probaby the 102 engines, too.

Idle roughness has been an issue since about 40K miles and was an issue with my former '84 190E 2.3. My suspicion is that it may be inherent to the CIS-E system as the low pressure at the injectors at idlel tends to amplify any small variation in flow characteristic resulting in uneven fuel distribution. This is an issue with the old Rochester continuous flow FI system on vintage Corvettes.

Does anyone have an explanation for the idle roughness and a solution?

Second issue is degrading emissions performance in California ASM (acceleration simulation mode) loaded dynamometer emission testing. As with most cars the toughest bogey is hydrocarbons at 15 MPH.

My first ASM test, 1/99, yielded 121 ppm HC at 15 MPH against a limit of 141 at 63K miles.

Prior to the 1/01 test I installed a new Bosch cap and rotor and a new set of H9DC plugs and the performance improved to 87 ppm against the same standard (68K miles).

I removed the plugs following the test and reinstalled them prior to the 1/03 test. The 1/03 test HC count increased to 113 PPM against a standard that was tightened to 116.

For two tests in a row my car has been tagged to go to a test only station because it has been identified as a high emitter, and this may be the case as the average for my year group is about half of what my car is measuring.

A '90 300E was also there at the same time and the owner squeaked by with 1 PPM to spare although I think the limit for that model was slightly different thnt my car. In any event, it appears that this engine family has high emissions, and I figure I'm going to fail the next test.

In asking around I have heard that the MBZ converter system lacks longevity, and it's also been suggested that the O2 sensor can drift out of calibration causing a richer than necessary mixture. (My O2 sensor is original.)

Does anyone has any insight into these issues?

Duke

P. S. It's interesting that NOx is quite low given that this engine does not have EGR, but I believe it was added for the '89 model year. The low NOx could be the result of a richer than stoichiometric mixture.
 
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