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RWD - Smog Trouble, High HC, 1994 940 Turbo

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Smog Trouble, High HC, 1994 940 Turbo 900

Hi all,

New to the board and looking for some advice. I’ve got a new-to-me 1994 940 Turbo that I can’t get over the hump with smog check. Here are my numbers:

HC 15mph Max 59 Ave 25 Meas 55 PASS
25mph Max 34 Ave 14 Meas 41 FAIL

CO 15mph Max 0.34 Ave 0.06 Meas 0.07 PASS
25mph Max 0.32 Ave 0.05 Meas 0.05 PASS

NO 15mph Max 692 Ave 263 Meas 542 PASS
25mph Max 711 Ave 221 Meas 426 PASS


This is the second time its failed on the 25mph HC level. So far I’ve put in new plugs, plug wires, distributor cap and rotor, ignition coil, and air filter, and changed the oil and replaced the PCV box. The car drives well except for a surging/hunting idle. I checked the codes after the first fail and got a 2-3-2/Lambda Adjustment/Too rich or lean at idle. After getting the code I tested the O2 sensor and that was fine. Fuel pressure regulator checked out OK too. I pulled the MAF while the car was running and the idle smoothed out and went up a 100 rpm or so, but I don’t know what to make of that. I’ve encountered conflicting information as to what happens when the MAF signal is non-present.

After I cleared the MAF codes I cleaned the MAF with sensor cleaner. Then I checked for vacuum leaks with a propane torch and couldn’t find anything. Took the car to get tested again and failed a second time, with the above results. Today I cleaned the throttle body, it wasn’t dirty but I did the job for due diligence.

Nothing so far has fixed the idle problem, and I have a suspicion that it is tied to my problem passing smog. I’m reluctant to throw down cash for a new MAF if I’m not certain its at fault. I had no MAF codes prior to disconnecting it. Tomorrow I’m going to put some Techron in the gas at fillup and try the italian tuneup.

I’m getting frustrated, any thoughts?






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New Smog Trouble, High HC, 1994 940 Turbo [900]
posted by  shaneturbowagon  on Sat Jun 8 16:55 CST 2019 >

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