So, I took my '88 300CE thru NJ bi-annual inspection last week. I FAILED!
14 years and 100,000 miles and it's never failed before.
Soooo... Is this a serious matter? what's the simple fix on this reading....or where to start.


Idle FAIL
HC ppm 257 Standard 220
CO% .38 1.20
CO2% 14.1 ____
O2% 0.6 ____


High Idle - PASS

HC ppm 39 Standard 220
CO% 0.37 1.20
CO2% 14.4
O2% 0.2

The usual change plugs / ohm out wires is another step unless they have been done recently ( like sub 30 K ) .

What causes high HC. What causes high Hydrocarbon - SmogTips.com. Failed HC Emissions. Why did my car fail the emission test for high HC emissions. What is HC. My vehicle failed the emission test for high Hydrocarbons. Why my car produced high HC. Hi

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

Since your problem is at idle only, I would suspect the idle circuit (idle air control valve, vacuum lines, etc.) While you're there, clean the throttle body and throttle plate. I'm not an M103 expert so can't offer much more than that.

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Prost!

My bet would be on the IACV vacuum line having a small leak -- not enough to make it run bad but enough to throw off the air fuel ratio slightly. If you have a multimeter I'd also recommend measuring the duty cycle. Chasing down fuel ratio issues on these cars are kind of a pain but in my experience it is old dried vacuum lines/connectors 90% of the time.


Sent from an abacus

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

You have a marginal failure, and the cut points are actually quite generous. Likely cause is catalyst aging. It's not running hot enough to use all the O2. As catalysts age they need to operate at higher temperature to achieve peak reaction efficiency.

Check threads started by me over the years on M103 emissions diagnostics. Shorting the R16/1 resistor and plugging the vacuum advance signal line may help, especially if the high speed test is done first. The retarded spark advance will increase EGT and increase the temperature of the catalyst bed so it will use more of the available O2 to oxidize HC during the idle test.

If the catalyst is operating at peak efficiency, the O2 content should be zero to no more than 0.1 percent. At 0.6 percent for the idle speed test yours is leaving a lot on the table. The high speed no-load test yielded only 0.2 percent O2, and you can see that the HC is dramatically lower.

Make sure you warm the engine up thoroughly by putting as much load as you can on it on the way to the test station. Never shut off the engine prior to the test, and while waiting turn on the defroster, which will engage the compressor and keep revs at about 1500.

I go to the drive-through place at a time when I am either first in line or go right on into an empty test bay.

Duke

Thanks for all the advice fellas.
TnBob. I'm going to review my service records to see when ignition work was last done. Since I don't use this as a daily driver any more, it may be some time, not necessarily miles since I had routine ignition work done, or the air filter changed.

Duke 2.6. I don't think it's the cat. No loss of power at high speed. However, I did go in with a "cold" engine. Normally I'll run it up and down the highway to get it good and hot, but since it's every other year and I needed an appointment before 12/31, I went in the middle of the work day.
I think the idle may be too low. It idles at just above 500 - say 600-650. What's normal idle for a 103?

I'm no DIYer, so, I'm just trying to get some possible problem areas to have checked out. My indie is a competent guy and lives in the neighborhood.
I'll keep you informed of the outcome.

An alternative thing to consider.

If you have the fuel purge system that draws off vapour from the fuel tank and chucks it through the charcoal filter and then into the inlet manifold you might find that excess fuel is reaching the system via this route.

Chapter 47 - 200 says to disconnect this system from the inlet manifold when performing tasks such as setting idle speed.

If this makes a difference then it might be time to replace the charcoal filter as well...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

600-650 is where both of my M103 powered cars would idle. I don't have any suggestions aside from what was already posted but if the car wasn't at operating temperature it could very well have been the reason for failing.

The catalyst can fail "chemically", but that won't affect exhaust backpressure or power, and as I previously stated "catalyst aging" increases the required bed temperature to achieve maximum reactions, which is why most cars see increasing emissions with time and miles.

If it fails mechically, then higher backpressure can lead to a noticeable loss of power.

Idle speed needs to be specfied in neutral for manual tranmissions and Drive for autos. My manual M103 idles at 700 in neutral.

Failure to get the engine/catalyst fully warmed up can easily result in a marginal failure, especially in cold weather.

Duke

I got mine to sneak by a few years by driving pretty fast, then keeping it as hot as possible before the test, and adding a bottle of "guaranteed to pass" snake oil to the gas. Also used brand new plugs.
But, the final fix was new injectors - lowered the HC idle emissions by 80 %.

Idle speed in gear is 600.

DG

Run a bottle of RedLine SI-1 Complete Fuel System Cleaner, ... not the other brands.

I have had slight idle issues and mixture issues with CIS & CIS-E systems many many times, tried so many things to make my cars run properly on good premium fuels, but the injectors tend to dribble at low flow rates eventually and need cleaning. This always seemed to happen before 50k miles.

After trying so many solvent-based cleaners (including the stuff that they sell at the Mercedes and Audi dealers) I tried the RedLine stuff, detergent based they say and not corrosive to the bearings like the solvent-based ones, it worked. My '91 300TE went from an occasional miss at idle and slight hesitation with part-throttle increases, to clean and responsive (in less than 100miles). IIRC that was in 1994 at around 50k miles on that car, I had already had the dealer try everything including walnut-blasting the valves for carbon, replacing the fuel distributor, coil, wires and plugs, running the (Chevron-Techron) Mercedes fuel injection cleaner. Nothing worked.

I'm not connected with RedLine, but do like this product and have run it as a maintenance fluid in all of my gasoline cars/boats/etc. since. Worth the $12 to try IMO. Dribbling injectors at idle will not give you clean exhaust.

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Gone to the dark side

- Jeff