High Hydrocarbon at idle

[lotzagoodstuff]

So I have to get my GN Washington emissions tested. The car failed due to a high HC number at idle. The car is bone stock, sat for 4 years, had bad fuel pump, it has a new fuel pump, all fluids changed, fresh tuneup, and no modifications. The idle quality is a little lumpy, but it idles down to 450 rpms in drive as verified by the emissions machine. I did change a couple of vacuum lines that felt soft, and then I went around with some propane and checked all of the vacuum lines. I did notice when I unplug the EGR, it seems to idle better, which tells me that might be the culprit. Cracks me up that the numbers are so good at 25 mph on the rollers, but not so good at idle.

Here's all the data I got today:

HC CO CO+CO2 O2 RPM
CRUISE LIMIT 150 1 6 N/A N/A
CRUISE EMISSIONS 88 0.17 11.47 5.16 N/A
CRUISE RESULT PASS PASS N/A N/A N/A
IDLE LIMIT 220 1.2 6 N/A N/A
IDLE EMISSIONS 449 0.44 8.84 8.94 460
IDLE RESULT FAIL PASS N/A N/A N/A


Any input would be appreciated.

R. J.

 

[Rebel]

Hc

HC is unburnt fuel from incomplete combustion. If disconnecting the EGR made a difference, I would think you would be mentioning a terrible idle, EGR hates idle (EGR closed) but starts doing it's job off idle. If that's the case clean/replace the EGR. If the idle isn't terribly bad I would suspect IAC or it's passages, leaky injector or something like that. If it was a bad plug, wire, coil, or module it should affect more than idle. What's funny is you can have high tailpipe readings from an actual lean mixture from the ECM over correcting. Also, since the car has been sitting, it may be carboned up. A simple fuel tank additive and a proper spanking might straighten it right up. Just my 2 Lincoln's, hope you figger it out.

 

[gofstbuick]

over 8% O2 content. Your engine is running really lean or in lean misfire

 

[lotzagoodstuff]

Thanks for the pointers, been many moons since I worked on any GM emmissions/electronics (I've owned a pile of EEC IV Fords over the last 15 years). I removed the throttle body and IAC today. Everything was very dirty, the IAC looked like it was only seating on one side of the cone and was very carbon fouled. The shaft was pulled all the way "in", in fact the spring was almost coil bound, which I suspect is bad as I thought the spring was in fact a "return spring". It was very difficult to move the plunger in and out, which I am guessing should move freely.

While I was in there, I cleaned the throttle body and upper and lower plenums. There was a small rectangular port at the front of the lower intake that was almost full of hard carbon. I cleaned most of it out, just wondering where does that port go and what's it's function?

 

[lotzagoodstuff]

Any IAC brands better than another?

One last question: are there any IACs to stay away from or any brand proven to be the best? I am thinking BWD as I thought they were always quality sensor/parts.

 

[RmvBfrFlght]

While I was in there, I cleaned the throttle body and upper and lower plenums. There was a small rectangular port at the front of the lower intake that was almost full of hard carbon. I cleaned most of it out, just wondering where does that port go and what's it's function?

EGR port. Goes to the EGR valve on the drivers side of intake.

RemoveBeforeFlight

 

[mikestertwo]

. The shaft was pulled all the way "in", in fact the spring was almost coil bound, which I suspect is bad as I thought the spring was in fact a "return spring". It was very difficult to move the plunger in and out, which I am guessing should move freely.

It is not supposed to move free. It is a stepper motor driving a lead screw. The spring is there to take any play out of the drive.

 

[lotzagoodstuff]

Thanks for all the input, cleaned it up and put it back in, recalibrated the TPS and IAC, running better but the idle quality is still pretty poor. Time for a ScanMaster I guess.

Thanks again for the help.