94 Toyota 22RE 4X4 fails low speed emissions smog test

[digital]

So it appears that I pass the high speed smog test no problem, however I fail the low speed emissions test.

While idling, you can see and hear the motor stumbling like it is missing or something. Any ideas of what to check first?

The guy at the shop said spark plugs, cap, rotor, etc.

Any help is appreciated!

 

[KLF]

What state are you in? This will help others from this state chime in with recommendations. What exactly are you failing for?

Start with what the "guy" said.

Have you checked to see if there are any codes stored in the ECU?

 

[GRM]

Make sure the engine is warm to get the o2 into closed loop. Clean out the EGR valve, then push the RPM as high as you can (I want to say california allows 1100). also not a bad idea to adjust the TPS at the same time. Then check or replace the plugs/cap/rotor/wires.

My last truck would always fail, until the state implemented the 'test only' system, where it is tested on a dyno at 15 mph and 25 (or is it 35?) mph and skipped the idle test. Never failed again.

 

[digital]

What state are you in? This will help others from this state chime in with recommendations. What exactly are you failing for?

Start with what the "guy" said.

Have you checked to see if there are any codes stored in the ECU?

I am in California, the smog hippies are killing me..

The check engine light doesn't come on so I assume there are no codes??

 

[digital]

Thanks GRM, I will check those out as well..

 

[pappy]

I would start with the Ox sensor as the probable issue, assuming high HC. I would give the truck a good tune up, including plugs, cap, rotor, maybe wires and a valve adjustment. An oil change can also help. Check the air filter, or just replace if you can't recall the last time. Remove and clean the throttle body. Check the PCV.

What were your numbers? Knowing what was high can help diagnose the problem. For instance NOX is reduced by the EGR.

 

[Bogo]

While idling, you can see and hear the motor stumbling like it is missing or something. Any ideas of what to check first?

The guy at the shop said spark plugs, cap, rotor, etc.

Also check the engine ground and battery connections. Your truck is old enough that they could be beginning to get too corroded.

 

[WristPin]

only nox is recorded while rollin the dyno.

 

[digital]

PASSED!

Replaced Cap, Rotor, Wires & Plugs. I cleaned up the corroded battery terminal and oiled my failing dashpot.

I believe what was happening was when I would let off the pedal, my dash pot was sticking, not allowing idle to return to 750rpm. It would hang around 1050-1100rpm.

Thanks for the help guys!