My D16Z6 in an '89 DX hatchback failed smog due to high hydrocarbons when I took it to the referee here in California. The wiring is converted to OBD1 and the emissions equipment is all hooked up properly for a '93 Si, so I can pass the visual part of the test. The car also doesn't seem to idle that well. It doesn't run terribly but the car seems to vibrate a lot at idle and the idle speed occassionally drops too low for a few seconds after letting off the throttle. I need a few ideas on what to try next.

The emissions were as follows:

15 mph 25 mph
RPM 1727 2806
%CO2 13.2 14.1
%O2 2.6 1.2

Allowable HC (PPM) 95 60
Typical HC (PPM) 21 13
Measured HC (PPM) 103 56

Allowable CO (%) .58 .57
Typical CO (%) .06 .05
Measured CO (%) .06 .04

Allowable NO (PPM) 798 864
Typical NO (PPM) 150 136
Measured NO (PPM) 57 32

The HC's were not much higher than the limit but I should have passed easily since I have a new O2 sensor and catalytic converter.

I just performed a compression test and had the following numbers:
186 184 179 176

Prior to the smog test the following work had been done:
Injectors were cleaned and balanced by RC Engineering.
All intake and throttle body gaskets and seals were replaced because I thought I had a vacuum leak.
Head was removed and taken to local machine shop where all valve seals and several valves were replaced. The shop is reputable but I do not know how knowledgeable they are about Honda heads.
The head gasket was replaced with an OEM Honda gasket when I put the head back on.
The old cam and complete rocker arm assembly were reinstalled as is. The cam looked okay to me but I did not measure the lobes. The rocker arms seemed okay to me, but I am not a mechanic, so I easily could have missed something. I did do the manual rocker arm inspection specified in the Helm's manual. Essentially the intake mid rocker arms did move independently from the primary and secondary rocker arms.

Since the smog test I did replace the coil, but it did not seem to affect the way the engine runs.

Other info that might matter:
The header and downpipe are from a D16Z6 but the exhaust behind the cat is from the stock '89 DX. Would the increased backpressure adversely affect the engine that much at low rpm?
I could not get the camshaft TDC timing marker to line up exactly when the crankshaft was at TDC. It was either half a tooth ahead or half a tooth behind. Is this normal and is it a problem? I suspect it is due to the head being resurfaced.
The engine does not seem to be burning oil as far as I can tell.

Thanks

 

Bribe the emissions guy into inspecting the car with the engine turned off.