I have a 1986 volvo 240 that seems to be running fine but with a small problem. Because I have a SMOG check coming up I have been doing a lot of basic maintance and while just reading through the Bentley manual I decided to check idle, 02 sensor, and mixture.

Idle came out right but with small 50rpm surges. The O2 sensor fluctuated between 0.4V and 0.7V which seems like that should be typical. The Dwell meter read 15 degrees when I was checking the mixture. The Bentley manual says that it should oscillate between 20 to 70 degrees and that if it is pinned I should make sure the 02 sensor is functioning properly. Since it was pinned at 15 I went back to look at the 02 and it was working fine. After reading some previous threads here I followed someones suggestion about grounding the 02 sensor lead and putting 1.5V across it was watch for the rpms to increase and decrease respectively. That went well. I also checked the ignition wiring harness for shorts but that turned out fine. From another thread someone suggested cleaning out the throttle body to increase performance, stabilize idle rmps and what not, so I did that. But I still have a pinned dwell reading. So, what is wrong here?

The only other direction I can think to go in, is to increase the mixture and see if that doesn't help. Does anyone know if this could be a reasonable cause for the dwell to be pinned at 15degress?

The only reason that I haven't played around with that is because of the anti-tamper plug.

Does anyone know if SMOG checks look at the antitamper plug, or the Dwell reading?

Any responses are appreciated.

PS: For a little background info my car didn't pass SMOG 2yrs ago. So, I changed a leaky head gasket, put in a new 02 sensor, new catalytic converter, and replaced the whole exhaust system with one of those IPD high flow 2.5" exhausts made for the 240. Then it passed SMOG. Some time after the SMOG check I put in a K&N air filter. For these reasons it seams like I might need to adjust the fuel mixture.