1994 XL 4.9L E4OD. NJ emission test - idle (sniffer in tailpipe) and high idle (truck running at speed with drive wheels in rollers, sniffer in tailpipe).
Allowable limit for both test - HC ppm is 220. High idle test results = 38 passed. (38!! is this a green vehicle??) Idle test results = 376 failed.
I ran the codes following the instructions on this site. (flashing cel.)
I get 3, pause, 3,longer pause, 1, longer pause, 3.
Does this make sense to anyone? Truck was tuned recently - cap, rotor, wires, and plugs, and seems to run fine. Any theories would be appreciated as I am way confused at this point!!

 

i had the same problem and i passed with flying colors
look up seafoam treatment and try high octane fuel

 

Can you post a picture of the entire test result? It helps to know what the readings are on the other gases.

 

mode: Idle-Fail
GAS READING- STANDARD
HC ppm 376 -220
CO% .58 -1.20
CO2% 13.0
O2% 2.1


mode: High Idle - Pass
GAS READING -STANDARD
HC ppm 36 -220
CO% .02- 1.20
CO2% 9.8
O2% 6.6

 

My first thought would be a slow responding O2 sensor.

On a two speed idle test, the high idle is the first test it usually has a 30 Second warm-up prior to the test. It will immediately go to the Idle test once this is complete. With a slow responding O2 your truck just doesn't have enough time to stabilize.

You threw me off a little bit though saying it was on the rollers. That type of test would have a fifth gas NOX. Even in that case I would still Say O2 sensor

 

Ok to be sure clear your codes, read the sticky again and record the codes properly. Going off what I think you said you have an error 33 and a 13. First thing to do with the ecu codes is clear and retest to see what repeats. Don't forget to allow the engine to warm completely. 33 is egr failed to open or close on test. That will screw up your idle nicely. Make sure the valve moves freely and check for loose electrical and vacuum leaks. Apply vacuum to make sure it opens and closes. Manually jump the relay wires to make it switch. 13 says idle speed control did not respond properly. Make sure your butterfly is not stuck and clean your IAC valve. But first verify those codes.

 

I disconnected the bat. to clear codes & then ran KOEO. Got the same results as above post. I then ran the engine running test and got the following 3 codes. 411, 538, 632. What do these codes say about my idle emission results and how would you suggest I trouble shoot this?
Thanks to all who respond.

 

On a 94 you should have 2 digit codes. Someone please correct me if I'm wrong there.

 

I've got 3 digit codes on my 94 5.0.