Make certain that your idle switch is not made (that is, the switch is open) at 15mph.

 

What is 'high speed' in TX? 25mph?

HC looks good at 'high speed', but excessive at 15mph. So, Wally's advice points to the most likely cause of the problem (high hydrocarbons due to low throttle enrichment).

 

Any vacuum leaks? If not this will do it (02 and TempII).

 

Are you driving it on a regular basis? It may be as simple as that. I bought a car that had not been driven much. We drove it about 300 miles and took it in and it passed.

 

?? How do I check this?

and to the other poster, yes, driven on a regular basis

 

None that I know of or can hear.. Suggestions on how to check? I know the hose in the ear trick but other than that?

 

You check the throttle switch with a multi-meter. Procedure is in WSM volume 1A, page 24-115 (LH Jetronics).

You can also test it with a diagnostic tester hooked to the diagnostic port. With digital dash, you can see the MPG jump when coasting as you let off the throttle.

 

Just make sure they run the test in 1st or 2nd gear on your 5 speed car. This will make sure they have to open the throttle a little to get it off the idle map on the low speed test.

 

I would also recommend you do a battery reset after you install the new O2. The LH may take some time to learn the new setup.

 

25year old car shouldnt need emissions test in TX. I know they didn't test mine

 

His car isn't 25 years old yet. Any follow-up on this issue?

Dan
'91 928GT S/C 475hp/460lb.ft

 

Yea, he took it to the place that does all the cars for me, it passed

Jim, how'd you find this thread?

 

I thought 89 came out in late 88...anyways... You can always just park it or take ur chances for 2 months ;-) ... I know I have been driving mine without inspection all year but I'm crazy that way

 

Sean... I downloaded new rennslist app and the thread came up under one of the tabs with a red 1....since this was a concern of mine at one time i put my 2 cents in :-)

Cheers

 

Ops... Sry I see the thread is an old one. :-) more coffee needed