high HC at idle

[nopain00]

My 91 Camry (3SFE) just failed emissions for a high HC at idle. I need some help making sense of the numbers and how to proceed. The results are:

IDLE (FAIL)
HC ppm 356 (220 standard) FAILED this one
CO% 0.06 (1.20 standard)
CO2% 13.8
O2% 2.0

HIGH IDLE (PASS)
HC ppm 106 (220 standard)
CO% 0.20 (1.20 standard)
CO2% 14.9
O2% 0.4

The ignition components (dizzy, coil, wires, plug [NGK]) are all oem and less than 6 months old. The base idle is set to 650. Timing is slightly advanced maybe 12 instead of 10 BTDC. The cat is original.

I ran through the algorithm in the FSM to check the O2 sensor by jumping the terminals in the diagnostics port and reading the voltage fluctuations. It's supposed to fluctuate 8 or more times in 10 seconds at 2500 rpm. Mine was just a bit shy, as it would reach its 8th fluctuation right after the 10-second mark. I can change my O2 sensor, but I'm not sure whether that would fix the rich at idle problem I'm having.

Any ideas? Thanks.

[Doctor J]

What is the mileage on the car?
Very low CO and elevated HC on idle are comonly seen if :
the engine has intake vacuum leaks;
low compression due to the leaking valves (causes idle misfire)

[nopain00]

It has 150K on it. I checked for vacuum leaks with propane. I checked around the throttle body, all of the vacuum lines, etc. Nothing.

Leaking valves may be possible. What do you suggest? Checking compression with a gauge or doing a leak-down test?

[sleep_deprived129]

I'd also check the charchol/vapor canister

[nopain00]

Originally Posted by sleep_deprived129

I'd also check the charchol/vapor canister

Oh yeah? I was under the impression that a saturated charcoal canister would increase CO. I'll take a look at it.

[scoathy]

not that it will fix your idle, but for the sake of passing emissions, could you increase the idle RPM?

[scoathy]

Did you check out the PCV hose and BVSV valve? According to the manual, those are two components that control HC emission.

[nopain00]

BVSV good.

Originally Posted by scoathy

not that it will fix your idle, but for the sake of passing emissions, could you increase the idle RPM?

Yeah, if all else fails, I'll just turn that screw a bit.

[scoathy]

Originally Posted by nopain00

Yeah, if all else fails, I'll just turn that screw a bit.

Good Luck! I just spent a solid month sorting out the NOx fail on mine... I don't wish that headache on anyone... LOL

[nopain00]

Thanks. Next on my list is to do a leakdown. Out of curiosity, what was the source of your problem?

[66conv6]

Mobil 1 synthetic for an oil change wouldn't hurt as it reduces by-products of combustion from oil on the cylinder walls.

[Doctor J]

Several notes:
1) when checking for leak tests look on the vacuum hose ends, including air-bypass idle up controls for a/c system and power steering pump pressure idle up valve as well as a boot between AFM and throttle body
2) with engine on normal operation temperature idling measure the voltage between Vf and E1 terminals of the diagnostic connector (do not jump T and E1) 5 volts will indicate lean idle mixture
3) adjusting the idle will not do anything for the engine with electronic idle speed control
4) perform leak down test on the warm engine
thicker oil helps to reduce HC if there are bad exhaust valve seals (post combustion leaks), HOWEVER in that case the CO readings were not too low (normal mixture)
the bandaid remedy for this situation can be installation of the "hotter" spark plugs just for the test and reatarding timing to 8 degrees BTDC. this modification may burn the hole in the piston in long run and produce high levels of NO emissions under load (which are not measured during TSI test)

[scoathy]

Originally Posted by nopain00

Thanks. Next on my list is to do a leakdown. Out of curiosity, what was the source of your problem?

Mine was failing NOx emissions both at idle and at speed. Extremely high numbers on NOx but all other emissions were good. I checked everything, one shop tested everything, still failed. I cleaned the EGR and EGR modulator valve and tested it good, still failed. I took it to a local performance muffler shop "Rich's Performance Muffler" in Wylie TX, they discovered the EGR modulator valve was failing. Swapped it out with a new one and passed with flying colors.

GL!