I have a 91 RS with a 305 TBI. I live in a county in washington that requires emissions testing. My car failed on the idle emissions and was almost double the limit. I found one cracked vacumn line and replaced that but do not think that would make that big of a difference. I had done the intake manifold gasket last summer and when I looked at the EGR port it was completely clogged with carbon so i cleared it out. Im wondering if there is a problem with the EGR valve not working properly or if it is something else. No codes are present as well. thanks for any suggestions

 

EGR valve is not be active at idle - ECM will enable EGR once VSS reads above 5 mph. Suggest that you post your sniffer test results.

//RF

 

Here are the results of the sniffer test

HC (PPM) Cruise limit 400/emissions 209 2390 rpm
CO (%) Cruise limit 3.00/emissions 0.68

HC (PPM) Idle limit 400/emissions 780 (this is where it failed) 690 rpm
CO (%) Idle limit 3.00/emissions 0.43

If this helps anybody point me in a direction I would appreciate it. Thanks

 

Based on your data it would appear that you have one or more cylinder misfiring. Unburned fuel will cause sky high HC readings. The CO reading of 0.43 to 0.68% range puts it in the 14.7 to 16.0:1 AFR range. If the engine was really running rich the CO readings would be well above 1%.

Did the report had CO2, NoX and O2 reading as well??

Check your ignition system thoroughly - plugs, plug wires, dizzy hat, rotor. A burnt plug wire will cause misfire which results in high HC levels.

If that does not help start looking deeper. Compression check - how good are the rings, worn valve guides allow oil to get into exhaust. A worn valve guide allows engine oil into exhaust resulting in high HC sniffer levels. Leaking injector will also cause higher HC readings as well, but this causes other emission parameters to shift.

 

the test also had the following numbers on it

CO+CO2 (%)
cruise- 11.53 idle- 11.30

O2 (%)
cruise- 5.1 idle- 5.2

I am hopefully going to do a basic tune up in the next few days and see what that does. I am thinking the plugs and wires have gone bad from sitting over the winter.

 

they shouldn't go bad over just the winter. IMO but easy way to check wires for arcing is in the dark I had a Jimmy had to replace wires twice in one year because arcing come to find out it was laying on exhaust manifold.

 

Here is an update. I did a basic tune up (plugs wires cap rotor) and got the HC levels down to the low 500 range at idle but still did not pass. My first question is how much would a partially plugged cat play into the HC levels? My other question is now that I have done the tune up my car is not idling correctly after it fully warms up. It started doing this after the sniffer test yesterday. Now the car will idle in gear and then the idle drops really quickly and most of the time comes back up but some times it does not and the vehicle stalls. All my wire connections are good and I have no wires touching the exaust manifolds. I am competely stumped as to what is going on. Thanks

 

@carfreakpeewee

Before jumping to any conclusions I would check and make sure that firing order and sparkplug routing to cylinders is correct. Yes, it is too easy to screw up - just your time and methodically go through it.
The sudden idle drops indicate that you may have a vacuum leak. A very common problem with TBI is the base gasket leaking - allowing un-metered air to enter. The IAC controls idle by varying amount of air that bypasses throttle blades. When it runs out of control range - i.e. fully closed, at 0 step count, it will no longer control commanded idle speed (stock around 600 RPM on LO3). If ECM senses RPM below stall threshold a stall threshold saver is enabled resulting in engine RPM flare-up. Check and replace base gasket (it less than $4 at parts stores). Go through IAC reset procedure - it is posted here in technical section.

Regarding CAT being clogged. When fully functioning engine is operating near stoechemetric AFR - i.e. 14.7:1 the HC levels should be around 100 ppm



and that's without a CAT! The fact that you have HC levels around 500 ppm indicates that you have either raw fuel or engine oil being dumped into exhaust! The CAT can only cleanup so much before excess HC bypass it and end-up at the tail pipe. The worst part of it is that engine oil coats active area of the catalyst rendering CAT useless! Now you see why it is a bad idea to have engine burning oil. These numbers would lead me to believe that you have worn valve stems, valve stem seals - a common problem in high mileage LO3.

//RF

 

I finally got a chance to replace the throttle body base plate gasket. I did find a small chunk missing on the inside of one of the two holes on the drivers side. After it warmed up I took it for a drive and it ended up having the same idle problem. I decided to unplug different sensors to see if the car ran any different. I unplugged the IAC and it still idled and tried to die and just turned on the SES light. Then I unpluged the sensor up by the thermostat housing and the car idled smoothly and did not suddenly drop like it has been. From what i understand this is the Coolant temp sensor and if it was malfunctioning would dump excess fuel and cause bad gas milage which I have started to notice. Does this sound reasonable as part of my problem? Thanks.

 

When you unplug CTS ECM will deliver fuel as if it was -40C outside - very rich mixture. From past experience this an indication of low fuel pressure due to either tired fuel pump or busted output hose between fuel pump outlet port and a feed through (inside gas tank). Occasionally low fuel pressure can be attributed to a clogged fuel filter. Before anything else perform a fuel pressure check - get a TBI fuel pressure gauge with a correct adapter - Actron CP7817 is one. Stock TBI is designed to operate fro 9 to 13 PSI (which is a wide range), but it will run as low as 6 PSI! You can check fuel pressure right where fuel lines jump from engine to the driver side frame rail.

//RF

 

How much does it cost to have an emissions test like this done? Sucks you have to deal with that hippy gov't BS.

 

And yet, without the need to pass emissions tests, he'd still be driving a gross-polluting vehicle with poor fuel economy.

That evil, "hippy" government did this guy a favor.